Old HVAC industry practices are holding us back and costing us money. But we can fix it.
I completely shut off my heat when it was -11 degrees Fahrenheit outside for an entire 24 hours to prove a point: my home’s heating system is wildly oversized and replacing that equipment with more modern technology will be much less involved than Local HVAC Company X probably thinks. One day in the not-too-distant future, I will undoubtedly be replacing my gas-fired forced-air furnace with an electric heat pump. Heat pumps, despite what your Uncle on Facebook might be yelling at you, are much better for the planet, and eventually (if not right now but due to variations in local energy supply costs I cannot give a blanket statement yet) they'll be better for your wallet, too. But if someone were to look at my current heating system, and that someone assumes my current heating system is actually appropriate for my home, which they very well might assume because it was specced and installed by industry professionals, they might conclude that I will need a very large heat pump capable of matching my current system’s heat output.
Here’s the thing, though - I don’t. Not by a longshot! My current heating system is between three and four times larger than it actually needs to be. And now I have solid proof to back it up. Which I will be showing you. That is indeed the point of this video. Before we continue, though, with this video, I want to try something different.
The video you’re currently watching won’t be that different: it’ll still be a wild ride where I explain way too much in my typically cantankerous fashion. But you may have noticed the runtime. Yeah, we’re covering a lot - also, I’ll apologize up-front, the teaser about shutting off my heat? It’ll be a little bit before we get there. But truthfully, the conclusions here are important and I want this to spread beyond my normal audience. So I will be releasing a condensed version tailored to a more general audience alongside this one on the second channel. If there are people in your life you wish to share this with, or you’re just short on time, that might be a better fit.
There’s a link in the description and right there. But for the rest of ya, well here we go. In the intro, I used the word "oversized."
That’s really what this video is about: determining the correct HVAC system sizing. By size, I mean the system’s total heating and cooling capacity. Systems come in different sizes because every home is different and how much heating and cooling that home needs depends on many factors. How big is it? How tall are the ceilings? How many floors? Where is it? What’s the local climate? Which direction are the windows facing? How many are there? How big are they? What’s their R-value? Are they low-E windows? Is there shading from trees or other structures? What building materials is the home made from? How old is it? How much insulation does it have and where? What kind of home is it? Single-family? Multi-family? Is there a basement? Crawlspace? Slab? Attic? And on and on and on. All of that actually matters when determining the heating and cooling demand a home will need, and that demand should dictate the equipment that gets installed.
But that’s a lot of variables to juggle, and if there’s one thing I know about humans, it’s that we’d rather things be easy than correct. So way more often than not (at least in literally all of my experience thus far) the main and quite possibly only variable that is considered is the home’s total floor area and HVAC system capacities get chosen using simple rules of thumb based on the geographic area you’re in, possibly tweaked by a sales rep’s observations if you're lucky. And that simply isn’t good enough any longer for many, many reasons. Which brings me to me! A while ago I moved into a fairly new townhome.
That term is kind of regional so in case you’re not familiar or it means something else where you live, it’s a kind of multi-family housing where one large structure is subdivided into multiple housing units which share one or more walls, but each housing unit has its own private exterior entrances. You might call it a rowhouse or something like that but they can be in many different styles. Since my home is fairly new and I’m sharing walls with neighbors, it’s pretty energy-efficient! My average gas bill in the winter is about $70 and my average electric bill in the summer (which includes driving by the way since I have an electric car) is about… actually that’s just about $70, too. Wild what denser housing options and efficient construction methods can do for our resource needs and thus wallets, eh? Before this turns into an urban planning video, though, my home’s current heating and cooling system is the very-typical-for-much-of-the-US-but-especially-here-in-the-Midwest centrally-ducted natural gas-fired forced-air furnace with central air conditioning.
The furnace is rated for 60,000 BTU/hr, and the air conditioner is a two-ton unit (which just means it can produce 24,000 BTU/hr of cooling). Now, the air conditioner was actually sized appropriately. Based on how last summer went, 2 tons of cooling is just about right for my home. But the furnace? It’s way too big! The heat barely ever needs to run even in very cold weather.
It’s almost comical how little my furnace runs. Lest you think I’m just being hyperbolic or perhaps unobservant, I have a smart thermostat which allows me to look at exactly how long it has commanded the heating and cooling system to run over a day. And I know for a fact that in the winter the heat is barely ever running. Here’s what a typical winter day looks like with my current heating system: January 5th was a cloudy day with the temperature hovering right around freezing point. With essentially no help from the sun, my furnace was providing the only heat to keep me warm and it needed to run for… 3 hours and 10 minutes total.
That’s all. We see this large spike in the morning when my program raises the set point to 69, but otherwise the furnace ru- sorry, *nice* - but otherwise the furnace runs for about 10 minutes per hour. At 10:00 at night my set point drops to 65, and then it didn’t run again until the next morning. With 24 hours in a day, and the heat only running for 3.16 of them, then the furnace only needed to produce about 13% of its total capacity.
If you know a thing or two about HVAC system design, then you should know that this is ridiculous. The heating system is oversized to an absurd degree if it’s performing like that when temps are around freezing. But... this is Chicago. It gets a lot colder than that. How about we look at that cold snap we had two Christmases ago? December 23rd, 2022 started out at a balmy -8 degrees (which is -22 for those who speak Metric).
Despite it being that frigid, the furnace ran for 6 hours total. 6 hours of 24 is a nice 25%, so even in that weather the furnace is barely taxed at all. Keen-eyed viewers may notice we don’t see that morning spike in this data - I was actually away from home during this period, so the thermostat was only maintaining 62 degrees (or not-quite 17 celsius) inside. That does mean that if it were maintaining my normal set point it would need to run a bit more, but not much - maintaining 62 in this weather is still fighting a 70 degree differential, so this is roughly equivalent to if I were home and the outside temp was 0 Fahrenheit, -18 Celsius.
Also important, since nobody was home, there weren’t any other heating sources in action like cooking appliances or human bodies to skew this data. Zooming out to look at more days, well it turns out that six hours is the most my furnace has ever run in a 24 hour period. Since it’s only spending at most ¼ of the time in a day heating, even in extreme cold, that suggests the furnace is oversized by a factor of four.
It’s four times larger than it needs to be. But, to account for the lower set-point and the fact that it was “only” -8 out there, I’ll fudge that and say that the furnace is oversized by a factor of three. Now, I wish I could tell you that my home is some kind of fluke.
But truthfully, I can’t - I have run across oversized heating equipment in pretty much every home I have ever been in around here. A friend of mine has a furnace which is so ridiculously oversized for their ductwork that they can’t even partially close any registers at all to help balance heat output between rooms without the thing tripping out on the high limit safety switch. I’m pretty sure that install was a hack job, so I don’t want to put too much weight on it, but even respectable, well-known installers in my area are routinely putting way more heating capacity into homes than those homes actually need.
You might ask, is that really a problem, though? So what if you have more heat than you need? Well, strictly speaking, it’s usually not a functional problem. Oversizing cooling equipment can lead to nasty issues - just ask my other friend who has a small two-bedroom slab-on-grade house built about 20 years ago and who just had a well-respected HVAC company conclude that three tons of cooling was appropriate for that little house. You bet that sucker short-cycles and can’t dehumidify worth a darn! Anyway, with heating equipment, having way more heat on-tap than is truly necessary doesn’t typically matter, especially with gas-fired heating equipment where energy efficiency isn’t impacted by cycle times much if at all.
When your heat source is gas, installers can get away with being quite sloppy. They just have to err on the side of too much heat. Nobody’s gonna complain about having too much, and older homes which are poorly insulated will need more than newer homes, so leaning on the high side is generally the safe bet. But this habit needs to die. We’re not gonna be heating our homes with gas forever.
Pick whatever reason you’d like, there are plenty. Heat pumps are in the news so much these days because they allow us to capture ambient heat energy from outside, concentrate it, and move it inside. That process is so efficient that we can end up with 3 or sometimes even 4 times as much energy inside our homes than we spend to collect it.
That is why they are such a big deal - it’s a way we can get more heat with less energy expenditure, and doing more with less is always a good idea. For that reason alone, more and more people will be using heat pumps as their primary or possibly only source of heat. They just make way too much sense.
And when speccing a heat pump system, actually installing the correct equipment with the correct capacity is very important! More than it’s ever been. Why? Well for the simplest of starts, you don’t want to pay for more than you need. Larger equipment is more expensive, but not just to purchase it.
Since heat pumps are electric sources of heating and cooling, larger systems require more electrical capacity to run them, and that makes everything from installation to considerations of backup power needs harder to manage! You really don’t want to be installing systems that are bigger than necessary but this old habit just keeps happening. It just happened last spring to my parents, a story I’ll be telling later on in this video. Why does this keep happening? Well, if you’ll permit me this speculative indulgence, I believe that a big problem today is the structure of many HVAC companies.
Any moderately-sized residential HVAC business seems to have separated the role of sales from those of service and installation. This might seem like a good thing - trained and licensed technicians only have so much time in a day, and their skills are too valuable to waste on free consultations. But I gotta tell ya, I think this division of roles and focus on speed over accuracy is causing a lot of headaches for everyone. Perhaps separating your team into sellers, fixers, and installers is efficient on paper - and maybe it is more profitable. But it also makes it difficult or impossible for anyone within those cordoned-off roles to develop the big picture perspectives necessary to correctly determine the best course of action for any given situation.
Another problem which is particularly rampant in cold parts of the country like mine where heat pumps aren’t yet common is, well, dishonesty. See, here’s a secret the industry doesn’t want you to know: Despite the cliche, I’m not really joking. Those fancy heat pumps we’ve been talking about? Turns out, heat pumps … ARE JUST AIR CONDITIONERS! That’s all they are! They’re just air conditioners equipped with an extra valve so they can operate in reverse to produce heat! Shout it from the rooftops, put it on a T-shirt, annoy your friends, and spread the word.
They are not magic technology or even new technology! They’re the same basic machines these companies have been installing for well over half a century with a few extra parts and, these days, smarts. Everyone in the industry knows this, at least I sure hope they do, but salespeople wouldn’t be good at their jobs if all they did was provide you with honest information. Price gouging on heat pump systems is abhorrent right now, and I have countless stories both personally and from conversations online of people getting $20,000 or even $30,000 quotes to install equipment which you can buy from online HVAC wholesalers for about 4 grand shipped.
And sure, there’s installation costs - people need to get paid, I know that. But there’s some magic money math going on when a central heat pump system costs 3 or 4 times as much as a new furnace and AC replacement. Because the heat pump part IS THE SAME THING as an AC replacement. One of the reasons I suspect people are getting such wildly expensive quotes to install heat pump equipment is that, due to the whole separation of duties I just went over and the old habits which just refuse to die, the folks coming out to give consultations are simply looking at the equipment that’s currently in the home and, so long as the homeowner doesn’t voice complaints about its performance, speccing a heat pump system to match the current system’s output. That is precisely what happened to my friend with the 3-ton AC in the two-bedroom house.
A 3-ton was there before so just slap a new one in, right? That’ll do. This tactic makes sense on the surface, but the problem is that seemingly nobody is doing a sanity check to determine whether or not the current equipment is actually appropriate for that home. And in my case, nobody did that when the home was built, either! Another thing I want to touch on is something that I keep hearing online. Many people with centrally-ducted systems who want to get a heat pump have been told that their ducts are too small to have a heat pump. I’m sure that this is true in some cases, but… if the person who told them that didn’t check to see if their current heating system is actually sized correctly, well then maybe those ducts are too small for the heat pump that person *thinks* they need but they’re fine for the heat pump that they *actually* need.
Keep that in mind as we continue this discussion. So, then, the next question of course is… how do you determine what’s actually appropriate for any given home? Well, here’s what's really frustrating - We have more and more tools to figure this out and it ain’t that hard. First, let’s discuss the increasingly common piece of tech which got this ball rolling in the first place: a smart thermostat. Having one can be extremely valuable.
Certainly I’m not going to tell you to rush out and get one and, also, I’m not particularly loyal to one system over another. Trust me, I get plenty frustrated with some of the asinine things they do - ask me about their ridiculous implementations of a hold function. If they even have one.
And while we're at it, Google - here’s a question for you: HOW ARE YOUR LOCATION SERVICES AND HOME/AWAY ASSIST FUNCTIONS **STILL** SO INCREDIBLY BAD‽‽‽ If my Android phone - A Pixel! With your own dang SOC! On which I have given the Google Home app full, unrestricted location access with precise location and WiFi scanning turned on happens to find itself on the same WiFi network as the Google Nest thermostat which is WIRED TO MY FURNACE and CAN'T MOVE oh, AND the phone can also can see all of those Chromecast-enabled devices on the same network, too, which you know belong to that home because the Home app is what manages all that crap, well then surely I must be home, right? I can’t have moved a mile or two down the road - in my sleep - with all that stuff still in-range of the phone, right? RIGHT‽ [clears thoat] Despite their irritations, a smart thermostat’s ability to log and tell you what it did over a day throughout the year is tremendously useful. That information alone, when combined with your heating system information, can get you extremely close to the actual heating load of your home. All you need to do is find a day where it was extremely cold and look at how long it ran.
With a simple, single-stage gas-fired centrally-ducted furnace, how long that furnace runs over a given period of time tells you how much heating it actually produced. It’s that simple. But perhaps you noticed there were some qualifiers there. Some fancy heating systems can actually run at two output levels, perhaps more. If you’re in that boat, data from a thermostat isn’t necessarily useless but it’s going to require more consideration than I can address.
And certain kinds of heating systems won’t necessarily give you such clean data at all, plus if you have zoned heating and individual room thermostats this all gets pretty complicated pretty quickly. But for many millions of you in North America, you have the same four-wire thermostat system that I do which only offers heating with fire, cooling with AC, blowing with fan, or nothing with off. As we’ve already determined, apparently my heat will only ever run ⅓ of the time at most in the coldest weather we ever get, which means I only really need ⅓ of my current heating system's capacity. Since currently I have 60,000 BTU/hr at my disposal, my actual heating load appears to be 20,000 BTU/hr at most.
And since heat is heat, we can convert that to a continuous power output of 5.86 kW. If I’ve done the math right and reality is as it appears to be, that’s the most heating power I should ever need to keep the house comfortably warm. Assuming that is correct, then to completely eliminate gas for heating I only need a 2-ton heat pump, which is perfect because that’s what my air conditioner happens to be. This is why I said this is gonna be easier for me than Local HVAC company X probably thinks.
I very much doubt many would believe that a home in Chicago would have the same cooling needs in summer as it does heating needs in the winter, but the data and my math shows this to be true. But have I done my math right? Are my assumptions here correct? There are some reasons to be cautious. Firstly, while my furnace is rated for 60,000 BTU per hour, I don’t have a way to confirm that it’s actually performing as-designed. Hopefully the installers hooked up a manometer to it and adjusted the gas valve according to the manufacturer’s specifications but I don’t know for a fact that that occurred.
Even if it did, though, well there are still confounding factors to consider. For one, the 60,000 BTU rating on my furnace is its input. With an annual fuel utilization efficiency of 92 percent, it’s only really outputting 55,200 BTU/hr when it runs. If anything that makes my math seem conservative, but it’s important to keep in mind. There are also two other minor sources of data fuzziness which reduce the accuracy of a data-logging thermostat. If you’ve ever noticed that your gas meter measures the gas flowing through it in a unit of volume but you’re billed for your gas consumption in units of energy, that’s because natural gas is just some crap we get out of the ground and its purity (and thus energy content) varies somewhat from day to day which your gas utility corrects for when billing you.
So even if I knew for a fact that my furnace were working perfectly, its actual heat output won’t be perfectly consistent. Also, the thermostat logs how long it calls for heat, but at every start-up, there’s a delay while the furnace goes through its ignition sequence so the thermostat is slightly overreporting total energy output. Now, to be clear, all these little sources of error are unlikely to amount to much, and two of them work in my favor anyway.
But it does mean that my 20,000 BTU/hr conclusion probably isn’t perfect. I still know my furnace is wildly oversized no matter what, but for now, let’s set the conclusions from the thermostat to the side. That’ll also make it fair for those of you without central heating or more elaborate setups. How else could you determine your actual heating needs? Why, with science! It’s time I introduce you to a little thing called a block load calculation.
Turns out, very few homes are built with exotic materials - and even then, with almost no exceptions we know the thermal properties of the construction materials we use to build homes. Insulation has an R-value which tells you its resistance to heat transfer. Windows have R-values, too - plus low-e coatings help reduce solar heating in the summer and reduce radiant losses in the winter.
The materials on the exterior of the home have an influence, too - an influence which those science people have quantified. And to tie this all together we have these tools called measuring tapes which let us gauge the size of walls and windows. If you actually take the time to assess these variables, you can do a load calculation which will tell you how much heating (and cooling) your home actually needs depending on where you live and how it was built.
For grins and giggles, I went and did one of these for my home! I used an online Manual-J calculator (manual-J is essentially the industry standard for how to do a block load calculation) and after inputting all my measurements, it told me that I’d need… 19,000 BTU/hr of heating with a design temperature of -15 and an indoor setpoint of 70 degrees. That’s awful-darn close to what my thermostat just told me, innit? Now, you may notice I have not shown you the results of this calculation (or even the calculation itself). That’s because I don’t really want to share too many details of my home’s specifications but also and equally importantly… I closed out the tab and don’t feel like doing it again. Plus, the site I used was very clunky and homebrew, and to be honest I’m kind of afraid of unleashing all of you on it. It seemed… fragile. I’d love to point you all to a good resource but honestly the way the calculation is performed is pretty intimidating, especially if you have the same visceral dread reaction that I do whenever I accidentally open Excel.
A more easy-to-use and guided manual-J calculator would be a very welcome thing, literally any of you watching who might have those skills and be inclined to build such a tool. I think, as the kids say, there should be an app for that. I’d love to play with it but more importantly, an easy-to-use tool for professionals in the field is very overdue. It has to be easy or it just won’t happen.
You may have noticed me use the term design temperature just a bit ago. Heating a home (or any structure for that matter) is a never-ending battle against heat loss. If it’s warmer inside than out, heat will seep out through walls and windows. Entropy’s just annoying like that.
And to maintain a consistently warmer temperature inside than out, you have to match that heat loss with a source of replacement heat. How quickly your home loses heat depends on all those factors I was talking about earlier, so one size definitely does not fit all. If there’s one thing to take away from this video, it’s that. But there is one factor that is universal: the greater the temperature difference between inside and outside, the faster heat will leave.
Doesn’t matter how big the home is or how well-insulated it is, that’s just physics doing physics things. Ultimately, that boils down to a simple temperature differential. A given heating system in a given home can only possibly make the indoor temperature X degrees warmer than the outdoor temperature.
The design temperatures are simply a way to relate that theoretical limit to your local weather conditions and a chosen indoor setpoint, so for instance around here, -15 Fahrenheit is about the coldest we ever experience, and if I want to be able to maintain a 70 degree indoor temperature in those conditions, well those are my design temperatures. -15 outdoors and 70 indoors. Really, though, that just means I want enough heat on-tap to keep the home 85 degrees warmer inside than outside.
And here’s something I get the sense relatively few people know. When a heating system is properly sized to a given home and its chosen design temperatures, then when we hit those design temps outside, the heating system will need to run nonstop - and that is normal. It might sound weird. But think about it - the design temperatures are the absolute worst conditions a heating system should expect to fight, and they only show up once or twice a year - if that. There isn’t actually a need to have any more heat capacity available than what the design temperatures dictate - especially when, even if the weather happens to dip below the design temp, a wide variety of simple supplemental heat sources, such as space heaters, is available for you to fill the gap.
That means, though, that there is at least one true benefit to oversizing a heating system. If you’re like me and like to turn the heat down at night to sleep a little cooler, a properly-sized heating system will take ages to get back to your daytime setpoint when the weather hits its design conditions. I’m of the mind that since this is a very uncommon circumstance over a year, that’s not really a problem. But some folks would probably be angry if they needed to whip out an extra heater in a cold snap to get the indoor temperature to rise quickly in the morning. This is undoubtedly another reason HVAC companies are prone to going overboard, and some manner of customer education is probably warranted here. The good news is that with heat pump systems, auxiliary back-up heating can be and often is installed and that can work alongside the heat pump to quickly raise the temperature when desired, at least if configured properly.
Anyway, we now have two sources of data that are telling me the furnace is about triple oversized. There’s what my thermostat has said with all of the home’s variables accounted for in-situ, and what the manual J calculation (which accounts for all those variables on paper) determined. The fact that they were within 5% of each other is pretty impressive, but both are still not quite what I’d call perfect.
To completely verify them, I wanted a way to be exact. No fudge factor, no guesswork, no weird variables - exact. And I knew just the trick! Through the magic of buying... [sigh] seven space heaters, I could design a test to find out exactly how much energy is needed to heat my home in the most extreme of weather.
All I needed now was a bunch of kill-a-watts, digital thermostatic controls, and some extreme weather. So I got some digital thermostatic controls, a bunch of kill-a-watts, and eventually the ol’ Polar Vortex turned up in the forecast. On January 14th we were in for quite the arctic blast. And I do mean quite the - low temperatures of -15 were predicted (that’s -26 for the French) and that’s just about as cold as it ever gets here. So I set to work. And now - here comes an important disclaimer.
I will not show you exactly how I set this test up. I’ll explain the gist and go over the many considerations I had to make, but I took a number of fairly big risks performing this test which could have ended up with frozen pipes or even a fire. I did everything I could to stay safe, and am happy to report that nothing happened but some good ol’ fashioned data gathering. But, do not try this yourself. It may not even be possible depending on your home’s wiring. So… why use space heaters? Well, electric resistive heat is as dumb as it gets.
A watt is a watt is a watt, and with a watt-hour meter I can quantify how much heat was actually produced by one of these things because the heater simply turns all of the electricity it consumes into heat. Space heaters here in the US are nearly all capable of outputting 1,500 watts of heat. And since apparently I don’t even need 6 kW of heat output, four of them running continuously should be all that I need to heat my home even in the worst weather we ever experience. But there are a few problems: first, I have more than four locations I need heat to come from.
I have 10 heat registers around the home and they were all placed where they were for good reason, though a couple are technically redundant. Second, while space heaters are rated for 1,500W, that rating usually assumes a line voltage of 125V. I typically get a little less than 120V at my receptacles, and after the bit of voltage drop caused by the heater itself, in my home the actual output of a resistive space heater tends to be around 1300 watts. So only having four might not be enough. But most importantly to setting up the test, a space heater maxes out the safe continuous load capacity of an ordinary 15A electrical circuit, and even 20A circuits cannot run two space heaters at the same time without the breaker tripping.
So before I could run this test, I would need to identify locations where I could actually plug all these space heaters in which were not sharing circuits. This was easy enough for me to figure out... after discovering that one of the outlets in the garage is on the same circuit as the bonus room the hard way, and I eventually identified five places where I could get power from and not worry about tripping anything. But it still required the use of extension cords. ♫ DUN DUN DUNNNNNN ♫ Extension cords and space heaters‽ Oh even worse! Remember how I bought seven space heaters? That’s more than five.
And actually I already had two and was using nine during the test! Which meant that splitters and power strips were involved, too! I wasn’t kidding when I said I took some big risks and said you shouldn’t do this yourself. So let me just say that again - do not do this yourself! But what sort of space heaters did you use, I hear you asking? Well - the cheapest kind you can buy! And not just because I’m a cheapskate, but because these are actually the best kind for simply heating a room for a test like this. The fan churns up the air to mix it around well and the resistive wire elements don’t produce much radiant heat so you don’t have to worry about weird hot spots or losses through a window. But even better, these cheap fellas are really useful given the constraints I had to work with and helped reduce the risks of a fire from those extension cords.
These basic fan-forced heaters usually contain two heating elements: a 600W element and a 900W element. That allows them to offer a low, medium (labeled "ECO" in this case because space heater manufactsss… nevermind) and high by using one, the other, or both elements together. Since the fan draws a measly 10 watts, that means you can safely use two of these on the same circuit assuming they are both on low or one is on low and the other is on medium. And since, in that case, the most one will draw is about 8 amps, using an extension cord isn’t quite so scary. But actually I used two more space heaters! Of a sort... Since I was shutting my heating system entirely off, there were two more things I had to worry about: the pipes in the cabinet under the kitchen sink (which is on an outside wall and above the unconditioned garage) and the insulated crawlspace where my water comes into the home.
Normally those areas get a bit of heat from the ducts running near or through them, but they wouldn’t during the test. So, I bought a couple of those little wireless weather stations and put their outdoor sensors in said crawlspace and under said sink so I could monitor them, and to provide those areas with a bit of heat, I threw in some incandescent Christmas lights. Who says you can’t be risky and festive at the same time? Those lights provided about 100 watts of heat in the crawlspace and 80-ish under the kitchen sink, and the weather station thingies proved that was sufficient. Now, every single one of these heat-producing devices eventually got plugged into one of five... these things: these digital temperature controllers allowed me to control the temperature digitally.
They simply take readings from their remote sensing probes and control the electrical outlet on the front through a relay. You tell it a turn-on temperature and a turn-off temperature and boom! You’ve got yourself a proper thermostat which can ~supposedly~ handle 15A of load. But 16 in Europe! Yet only 10 in Australia. But 13 in the UK! Are there any safety certifications on - that’s not important, what’s important is the house didn’t burn down and these allowed me to control the space heaters... and Christmas lights with precision! For the test, to hopefully mimic the heating characteristics of my central system, I put the actual space heaters near to where the heat registers in my home are (which is along outside walls near windows and doors as they should be. They got that part right!). Then I set the temperature controllers up in the five locations I was powering everything from and positioned their sensing probes in central areas of each room away from the heaters.
And, of course (and of utmost importance), each one of those was plugged into an energy monitor so I could see how much energy was used by each set of heaters. Total them all up over 24 hours and I could get a near-perfect figure. In pursuit of that perfection, the night before the test began, I observed the measured temperature of each controller both when my furnace began heating and then stopped, then I programmed the controllers to keep the rooms they were in within that same temperature band.
I did this to mimic the little room-to-room variations that naturally occur due to the system being centralized. And for good measure, I had some of my trusty data loggers set up to verify for you that the heaters were actually doing their job. Oh, I also put one outside to measure the outdoor air temperature for myself in addition to pulling data from Weather Underground. With the final setup, I had somewhere in the neighborhood of 6,500 watts of heat distributed throughout my home.
Based both on my thermostat data and the manual J calculation, this should not only be enough to keep everything warm, but the heaters shouldn’t even need to run nonstop. All that was left now was to wake up the next day and start the test. At 8:00 AM, the observed temperature outside was -11, and after resetting all of the energy monitors, it was time to switch on the heaters and switch off the furnace. Before long, the temperature controllers had all started turning on their heaters (and Christmas lights) and now, all that was left to do was watch. And, as expected, despite it being extremely unpleasant outside (and pretty windy, too) the heaters were more than enough. Before long, the first temperature controller was satisfied and the heaters it controlled had shut off.
Then the next one. And then the next one. Of course, they kicked back on, too, but the fact that the heaters were sufficient to raise the indoor temperature - even when the outside temp was 80 degrees colder than inside - was very good news.
However, when I began this test, the sun was up. The one consolation we typically get here when the arctic blasts rear their ugly heads is that the sky tends to be cloudless, so it may be life-threateningly cold out there but hey! At least it’s a bright sunny day! This also meant I’d be getting a bit of solar heating, though, and where exactly I’d get it would vary throughout the day. This didn’t matter for the data - I was taking measurements from each energy monitor every four hours, so I could remove the daytime period if desired. But it did mean that I had to fiddle a lot with the setup - especially on the main floor which is mostly one big room. Two thermostats and their heaters were in that room on opposite sides, and that meant that they’d fairly often influence each other in odd ways. Eventually, with some adjustments to the set points, I got them to cooperate.
But then, night fell. With no more sun coming through the windows, what would happen? Would the heaters be enough? Yes. They were. The two on the main level did need to run nearly continuously but the heaters upstairs were cycling on and off all night - by my rough estimation they were only on about 60% of the time. Oh but wait, I don't need any rough estimation, I know exactly how much energy was used during the test! And the answer was - drumroll please [extremely brief drumroll] 110.76 kWh, representing an average power draw of only 4.61 kW.
Excluding the daytime hours, from 8PM to 8AM the heaters drew 61.38 kWh representing an average draw of 5.115 kW, or 17,452 BTU/hr. That timeframe was also long after I had made dinner so no additional sources of heat were present. According to my probe the outdoor air temperature was between -9 and -11 degrees, which matches nicely to the data gathered at O’Hare. This means our Manual-J calculation was only 1,500 BTUs/hr off, but since the test occurred with outdoor temps just a little higher than my design temperatures, I mean I’m gonna call that spot-on. Whaddya know, science works! Spread the word! And here is what the indoor probes show us.
This probe was placed next to my home’s thermostat. During the day, the moving sun and all my fiddling to deal with that caused this dip here but after the sun set the measured temperature was right smack dab in the middle of what the thermostat and furnace normally maintains. And in the other two rooms we see the same thing - in fact it’s even more consistent. Also note that I did not adjust the thermostats overnight - they nicely maintained 69 degrees all night long. So - given that a real-world, actual test with actual data just occurred, I can state confidently that just a hair over 5 kW is in fact the actual amount of heating output I need to keep my home comfortable in any weather condition which verifies both what my thermostat was telling me and what a Manual-J block load calculation determined.
So sure enough, my furnace is more than three times larger than it needs to be. That is objectively silly, but it’s excellent news. Because I’m in a townhome which was built assuming everything that could be gas would be gas, even the dryer, I only have 100A electrical service.
Many folks would consider that an insurmountable barrier to electrification (although, as I’ve already covered, there are many ways around that). But in my case, well now I know that the circuit for my two-ton air conditioner is probably sufficient for the two-ton heat pump I’ll need, and for backup resistive heat, I only really need 5 kW available. That by itself would be sufficient to at least maintain a reasonable set point, but in a modern heat pump system the heat strips and the heat pump will work together, so I’ll probably have at least 7 or 8 kW of total heat output whenever I need it, which is more than enough. To be clear, it’s not like ditching gas will be painless for me. I’ll still need to run a new circuit to the furnace closet to have backup electric heat, but 5kW of heat strips is only a 20 amp load which makes it much more manageable. "mmmbut what about the ductwork?" I hear some of you asking.
Since you used space heaters during your test and shut off the furnace, you couldn’t account for any losses from leakage in your ducting! Ah, that's very good point, except no it isn't. I don’t have any losses to account for. Why, you ask? Fair warning, I’m about to get snarky! See, I am a Midwesterner and I live in a home that was built by my fellow value-obsessed Midwesterners.
And ya know what value-obsessed Midwesterners would never in a million years consider doing when designing a home’s heating system? Running its ductwork through an attic or a crawlspace. And ya know why we wouldn't do that? Because that makes no effin’ sense! OK sure, you’ll find that occasionally around here - sometimes compromises have to be made particularly when, like, doing additions or remodeling. But ya know where my ducts are? They’re inside the conditioned envelope! They go through wall and floor cavities all in the center of the structure, not once ever going above the ceiling into the attic, below the floor into a crawlspace or through outside walls. So, any heat that might leak out of them ends up where I want it anyway! It’s wild! Did you know you could do that? I know that some builders sure don’t. This may come as a surprise, but it turns out that if you put ALL the heaty cooly bits inside the place that you're paying money to heat or cool, you get ALL of your money’s worth and not just most of it. And if you’re thinking “oh, well he’s in the Midwest, he’s gonna have a basement” - get a load of this - I don’t have a basement! My home is slab-on-grade, so my furnace is just in this room! It’s in this closet! Just because you don’t have a basement doesn’t mean it has to go in the attic - or a crawlspace.
It never has to go there! It could just be here, inside your home, in a closet in a room and all the ducts it feeds can stay inside your home, too! This has always been an option and all it takes is planning a space for this stuff to live and not making it an afterthought. I feel so sorry for HVAC technicians in parts of the country where you stuff all this crap in an attic. Crawling through a little access hatch and tiptoeing on the joists just to read an error code - it could be just… right here! Easily accessible in a utility closet that's barely any bigger than your average bedroom closet. My water heater’s even in here! And guess what? If my AC drain clogs, it ain’t gonna ruin the ceiling. It’ll just puddle its way to the floor drain.
Imagine that! And ya know what really gets me? This article on the Department of Energy website makes it sound like this is some kinda revolutionary idea! “In recent years, energy-saving designs have sought to include ducts and heating systems in the conditioned space.” - pfft, recent years‽ Listen, we figured that one out like… forever ago. How has it taken the rest of you so long? The house I grew up in will be 100 years old before too long and ya know where none of its ducts were going? THE ATTIC. Because the people who built it used their brains! And don’t give me any crap about ceiling vs. floor vents, "oh it’s better to have ceiling vents in warmer climates" - First of all, we need plenty of cooling here, too and the floor vents are doing just fine. It’s forced air, y’know.
Plus, ever heard of a ceiling fan? And if you absolutely insist that they be in the ceiling, you could be running ducts below the ceiling and enclosing them in decorative soffits and if you’re so vain that you’d rather it be pretty than efficient, you probably think this video is about you and also - look up what a plenum truss is. You can have both. There are so many better options than “stick the thing up in the attic and make a spaghetti octopus of flexiduct, that’ll do.” Thinking about how much energy is wasted — and money! — just because sticking everything up in the attic is a bit prettier and cheaper is the kinda thing that keeps me up at night.
Maybe you think that’s strange but I think I'm strange, too. I’m also a liar! I actually do have two runs of insulated ducting going through soffits in the garage which is an insulated space but not technically a conditioned space. Those ducts feed the kitchen registers and, since some heat does get lost to the garage through leakage, well that should ideally be accounted for. Now, good news, I did. I will also fight you on whether that run of ducting should count as a loss - if it keeps the garage marginally above freezing, which it does, then I would call that a useful loss and is a useful loss even a loss at all? Yeah - chew on that one, philosophers.
Anyway, during the test I had yet another heater on yet another thermostatic control to keep the garage at 47 degrees, which I know for a fact is warmer than it would ordinarily stay because I run that setup (with a more legit plug-in thermostat) all winter and it does indeed need to run from time to time. The furnace alone will not keep the garage at 47 when it gets extremely cold. With another energy monitor monitoring energy, I know that from 8 PM to 8 AM, keeping the garage at 47 degrees entirely with a space heater (and I had my car unplugged, for the record) took 9.76 kilowatt-hours, representing a continuous draw of about 800 watts. That’s probably pretty generous, and I’ll bet the actual loss from those ducts is closer to 300 watts.
Maybe not even that. So. Now comes the part where I ask - why the heck is my furnace so big in the first place? Well, I don’t know for sure but I’ll bet the HVAC company hired to install this system just looked at the square footage figure for my home, maybe considered that it was a townhome but could very well not have, then just slapped in whatever furnace the supply house had handy and for cheap which was the next-size up from their ol' rules of thumb.
That’s actually another problem here - because oversizing a gas heating system doesn’t matter that much, supply houses can just stock a few common sizes to take care of 99.9% of all the housing stock in their area and that means they buy a lot of those machines, economies of scale kick in, and everything is self-reinforcing. It's not great. In the case of my home, I wasn’t there for the process of speccing the equipment so that is just speculation on my part. But last Spring, I saw this very thing - HVAC folks shooting from the hip without any sort of thought - in action. My parents decided to join the revolution and got themselves a cold-climate heat pump.
Likely due to a combination of the fact that nobody knows what heat pumps are around here and the general character of the builder who built their all-electric home, they never had a heat pump. They just had a big ol’ air handler with 20kW of heat strips which would come on like a giant hair dryer, and a 3-ton air conditioner provided cooling in the summer. When they inquired about a heat pump, the sales rep who came out to give them a quote saw that 100A circuit powering the air handler and, likely assuming that that was actually appropriate for their home, determined that a 5-ton heat pump system would be necessary. But see, they, too, had a smart thermostat in control of their heating system. And by looking at historical data and system performance, I determined that the most heat output they’d ever needed was about 10 kW, which is 34,000 BTU/hr. In tonnage, that’s just shy of 3 tons.
The heat pump series they were looking at is capable of maintaining its full rated output at 5 degrees Fahrenheit, and in those temperatures their home probably only needs about 8 kW of heat. Since three-tons was sufficient for cooling in the summer, and a three-ton Bryant heat pump is supposedly able to output almost exactly 10kW of heat even at 5 degrees, jumping up to a 5 ton would have just be overkill. Luckily, I was able to convince the sales rep that a 3-ton system with 15kW of backup heat would be OK. And that’s what they installed. And I’m very happy (and, to be honest, relieved) to report that I was correct. They had no issues in the summer staying cool, (in fact this system can actually produce about 4 tons of cooling despite being classified as a three-ton) and in that cold snap I ran my test? Well, here’s what that looked like for them according to their thermostat.
Even when the outdoor temperature was solidly below zero, their heat pump could produce all the heat they needed. To be sure, this was right on the edge - the thermostat was constantly calling for heat and I’m sure the heat pump wasn’t running very efficiently. But the thermostat didn’t call for backup heat until the outdoor temp had hit -12. Only then did the indoor temperature fall three degrees below desired, and that’s the point where their thermostat is configured to kick on the heat strips.
And even then, it only tickled them a few times in the dead of night. This cold snap was the only time this winter where the heat strips were truly necessary despite it being extremely cold and despite only having a 3-ton heat pump. A 5-ton unit would definitely have been overkill. So why did the sales rep think a 5-ton unit would be required? Well, based on how we used to build homes around here, and the general character of weather we get, it makes sense to assume you’re going to need more heating output than cooling, and that assumption would only reinforce using the existing heating system’s output as a valid benchmark. And remember, there is at least some benefit to oversizing the heat source - when you hit the design temp outside, a properly-sized heating system cannot get your home any warmer than the indoor design temperature. That’s precisely what was going on in the data here - they had reached equilibrium where the heat added by the heat pump was exactly the same as the heat leaving through walls and windows so it wasn’t making their home any warmer despite running constantly.
Once it gets colder outside than that equilibrium point, then the house starts to lose energy and some secondary source of heat is needed. With a fully-electric heat pump system, that secondary source is your resistive backup heat - the heat strips. But if you only have a gas furnace, you usually don’t have a secondary heat source. So, rather than explain to their customers that it’s quite normal for your heat to kind of putter out when it’s 10 below outside, go get some space heaters if you’re too cold, installers can just chuck in a furnace that’s a little bit bigger than it strictly needs to be and avoid complaints.
Which, to be honest, is completely understandable. I get why that’s common practice. But here’s the rub: everything is changing. For a start, we have been building homes in a more energy-efficient fashion lately.
At least around here. My mom and dad’s home is about 15 years old, and it actually has the same heating demand in extreme winter weather as it does cooling demand in the height of summer. I’ll bet very few HVAC people would believe that to be true but… it is! I have the data to prove it. And sure enough, my new home is in the same situation. I have a 2-ton air conditioner right now which has proven perfectly fine, and, well, now I know that a 2-ton heat pump will work just fine for heating, too! Remember, that’s especially good to know because I only have 100A electrical service.
So where does this leave us? Well first, let me say this to the HVAC contractors of the world: You have got to stop using simple rules of thumb! The world is changing so your habits need to, as well. For one thing, a home built in the 1990’s or later is a whole different animal from one built 50 or 60 years ago. But also, you can’t just be looking at someone’s current equipment and assuming what they have now is actually correct or necessary.
Of course people will be satisfied with a wildly oversized heating system - it’ll heat just fine, and fast! But just asking “does it heat well?” isn’t enough. At least around here, most people have heating systems that are oversized up the wazoo. Which is making heat pumps seem a lot harder than they actually are. As I hope to have shown in this video, there are several ways to concretely find out what sort of heating and cooling system you actually need. You could do the crazy thing and set up a bunch of space heaters on kill-a-watts. You could also do an actual load calculation to work this out on paper.
Or you can gather data from a logging thermostat, verify the heating and cooling output of the equipment it’s controlling, and actually find out what sort of heating and cooling was needed in what sort of weather with all of the variables and vagaries of that home’s heating system, building materials, size, orientation to the sun, all that accounted for in-situ. That worked perfectly for my mom and dad and for me, too. Of course there are plenty of smart thermostats on the market right now which will let you see this data, and hey, HVAC people, if you’re working with a homeowner who has a smart thermostat, you should learn how to get to this data (in case they don’t know how) and ask them to show it to you! You are leaving extraordinarily valuable information on the table if you don’t look at what’s already there. Now, I get it - change is scary, and hard! It’s much easier to just do things as you’ve always done them, and these new heat pump systems are more complex with more variables to consider than the furnaces and air conditioners you’re used to. Plus, when you have customer satisfaction to be concerned with, it is often a safer bet to go overboard.
In my heart of hearts, I know this is what’s happening. I’ve spent my time in customer service, and we all know there’s a particular kind of customer who just isn’t reasonable. That customer will simply never find a properly-sized heating system to be acceptable no matter how hard you try to explain to them that "yes, actually, it should be struggling when it gets extremely cold outside because it’s extremely cold outside! If you need more heat, plug in a heater or maybe just bundle up."
And the worst part is you don’t know who that customer is gonna be until it’s too late and they call to chew your head off. Trust me. I get it. But we have to push through this. We all do.
Proper load calculations should be way more common than they are these days. Especially because there are more and more tools available to do a lot of the gruntwork for you. Perhaps you’ve seen those apps contractors are using where they just take photos of your house and it spits out extremely accurate dimensions.
Somebody could build that for HVAC folks and your sales calls would probably impress. Also, for the love of all things holy, be honest with your customers about what heat pumps are! Yes, there’s government money on the table to help people get them but don’t be evil — that’s right, I said evil — and exploit that money to pad your bottom line. Help people out. For reference, this is essentially the same equipment that my parent’s just had installed.
Yeah, it’s a different brand, but the OEM is almost certainly the same. Ever see that Tyler Perry movie? Midea Builds a Heat Pump? Anyway, this website will ship everything to you, including a lineset, a thermostat, and the heat strips, for about $4,000. They even sell Mitsubishi equipment for not much more.
To be clear, I am not endorsing this product line or website… but if a contractor will replace your furnace and AC for you for $5,000 all-in but wants $15,000 or $20,000 for a heat pump… well maybe show them this? Let them know you know what’s up. Even if they need to hire an electrician to run a circuit for heat strips, some of these quotes I keep hearing about are pretty fishy. Another thing that we all need to consider is whether heat strips are even necessary any longer.
With the development of cold-climate heat pumps, in many places they just aren’t. Heck, they’re barely required here in the frozen tundra of Illinois. I’d personally still want them as a backup in case something goes wrong with the heat pump itself, but remember that I kept my house warm with a few space heaters. If I had just set up four of them and left the HVAC fan on to move heat around to the whole house, I mean that would work well enough in an emergency! And if you just can’t bear the thought of not having a fossil-fuel at your disposal, just get yourself a Little Buddy heater and a grill bottle of propane. Then crack a window open ‘cause that’s nasty. I don’t really have a clean conclusion here, but thanks for watching anyway.
I hope this doesn’t come across as too angry at HVAC professionals - you folks in the field all rock! Your companies and their practices… well I have my concerns but I’m sure you do, too. And I didn’t even touch on insulation! Add more of that to your home and all this gets easier! It’s no doubt thanks to recent building codes that I can get away with a 2-ton heat pump and my mom and dad, in a big, single family home mind you, can get away with a 3-tonner. There’s a lot to do when making any kind of change, but first and foremost you need to see where you’re actually at. Professionals could - and I’d argue should - do that for you as a matter of course. But hopefully this video gives you some ideas on how to help yourself.
And with that… the end. ♫ appropriately smooth jazz ♫ If my android phone, a Pixel with your own dang SOC, on which I have given the Google Home app full, unrestricted location permission with precise location and wifi scanning turned on, happens to be on the same wifi network as the Google Nest thermostat which is wired to my furnace and can’t possibly moved… ahhh!!! …kilowatt-hours, representing and average draw of 5.115 kW, or seventeen thousand four hundred fifty [ ] two BTU fuff They’ll be better for our wallet tt too. What happened there? …and I know for a fact that the winter.
Fark! Are simply looking at the equipment that ke fphsasf asf fha! Get a load of this guy, talking about heating loads. He should really try a new heat pump on for size! OK, gonna level with you, running out of puns for this one. GOOD THING I'VE GOT AUXILIARY PUNS! I'm prepared for any condition.
2024-03-10 22:17
