Is my furnace too small, or am I a demon customer? Do I need a lawyer?
February 14, 2020 8:47 AM   Subscribe

5 years ago we bought two new gas furnaces and air conditioners. Since then we've had dozens of service calls for a myriad of issues. But the biggest issue remains -- our house can't maintain a temperature in extreme cold/heat. Details inside.

About 5 years ago my wife and I bought 2 new furnaces and air conditioners. The set-up matches what we had before: one set is for the first floor and basement, the other for the upstairs.

The upstairs one has been pretty good. The downstairs one is sized larger and has stepping functions to reduce gas usage.

Part of our reason for upgrading was the old furnace was not doing its job after we added on a home theater, adding about 800sq ft to the first floor. That theater has ALWAYS been a problem. Before the new furnace the theater would regularly drop to 50-60 degrees in the winter, and be over 95 in the summer. We hoped a new furnace would regulate that.

To go further, we implemented zoning. Despite hiring an inspector to validate the work, I never felt confident the contractor we had built the theater in such a way that it would heat/cool correctly.

Well, in the past 5 years we have had dozens of service calls about our furnace/ac. Yes, the theater did not keep its temperature and the main area would drop as well. (The third zone, my grandmother's two rooms, is always plenty warm). The HVAC company kept blaming external factors and we spent $5,000 with a (different) contractor adding more insulation to the ceiling and closing off the crawlspace (despite the original contractor saying that would cause mold).

Switches have gone out on the furnace, we had to have our thermostats replaced twice, and we've had the furnace die in the middle of the night three times (due to the aforementioned switch issue and, they claim, ice build-up in the exhaust pipe).

Well, here it is in the depth of Illinois winter. It got to -7 out with a -25 wind chill. And sure enough, set to 72 degrees the theater dropped to 68. The main area, set to 74 degrees, dropped to 69. (My grandmother, being 99, likes it warm. Her 76 degrees remained constant).

At this point we feel there's nothing the HVAC company can do to fix this. Today the furnace isn't broken, it just can't keep up with the cold. We suspect they sold us a furnace undersized for our first floor.

We talked to the owner of the HVAC company who came back with this:

We size all equipment per Manual J, Energy Star, and manufactures recommendation. Typically 69 degrees on a day that is below zero is considered within the norm. Now to speak out of both sides of my mouth I also understand that people want to be comfortable in their home. But we do want the life of the equipment to be as long as possible and we want the energy usage to be as low as possible. In our climate we have typically 2-4 weeks of extreme heat and 2-4 weeks of extreme cold. We try to size accordingly to handle those day, but we also want to be aware of the fact that there is still the majority of the year where the outdoor temps are not extreme. Since the majority of the time we are not in extreme conditions we try to size more for the average temps. By doing so we can get better air exchange and cycle rates, lower energy consumption, more even temps in the home, better humidity control, and a longer life span on the equipment due to less short cycles.

We are definitely open to discussing changing the equipment, but my honest opinion is I would not increase my equipment just for a few days of the year. Even in this case, here in a couple days its going to be well above zero and then the temps will come up in the home.

So at this point...who is right? Is it normal for a furnace to not maintain a temperature during extreme heat/cold days? Or did they sell us a furnace that was insufficient for our needs.

AND if they did sell us insufficient equipment, now that it's 5 years later, what recourse do we have to not have to pay for full replacement? Should we get a lawyer?
posted by arniec to Home & Garden (30 answers total) 1 user marked this as a favorite
I’m with your contractor here- the idea that some parts of your house might be single digit degrees cooler than the thermostat during the coldest parts of the year seems entirely reasonable. Forced air heating is not a perfectly exact science, and as he noted, there are going to be trade offs with putting in an oversized system as well. An option might be to put in supplemental radiant heating in the places that are colder, or to add even more insulation.
posted by rockindata at 9:05 AM on February 14 [9 favorites]

I can't speak to the other issues, but I agree with the owner of the HVAC company in that it is not desirable to size your equipment for the extremes. I say this as someone who is (also in Illinios) currently working from home today and wearing a blanket, hat, and scarf, and running a space heater, because if I turn the thermostat up higher than the low-60s it can't keep up and just runs constantly. It's about 58 downstairs right now and 63 upstairs with the thermostat set to 62, though we don't have two zones and do have a section of our house with a vaulted ceiling that exacerbates the heat rising. When the thermostat was at 66 yesterday evening, upstairs was 71 and downstairs was 61 with the furnace running constantly.

I do have a furnace that is fairly oversized, turning over a huge amount of air at a time, according to a recent repair person. It pulls so much air, in fact, that we can't use the heavy duty air filters without it making a horrifying whining noise as it tries to pull more air than is possible through the filter. Despite all this power it still can't overcome the extremes of the temps and the inefficiencies elsewhere in the house (original, poorly sealed front door, lack of insulation, etc.)

In the summer we have to run a portable A/C unit in the bedroom because we just can't get the upstairs cooled with the central air, though there are a lot of other factors (radiant heat coming in via uninsulated roof, heat rising, possibly undersized central AC unit). Looking around at the houses in our neighborhood with central air I often see window/portable units upstairs, so this isn't that uncommon at least for the age and type of homes. My house is a bungalow built in 1921, so if you're in a modern house, perhaps expectations could reasonably be different. Personally as I contemplate putting on a pair of gloves I would be thrilled to be at 68 degrees right now.
posted by misskaz at 9:11 AM on February 14 [3 favorites]

Is this home theater insulated? A single room that's a later addition that tends to swing farther out during temperature extremes sounds like an insulation issue more than an issue with just pumping more air. No furnace is going to be able to maintain the temperature of an uninsulated room.
posted by GuyZero at 9:16 AM on February 14 [2 favorites]

GuyZero - it is insulated. I had an inspector come out and inspect the insulation after it was built and he said it was good. Then I had a different contractor come out and insulate even more. ANd it's better, but not right.

And to reiterate something above: My grandmother's area stays a balmy 76 degrees no matter what the temperature is outside. I can't figure out why that area can and the rest of the floor can't (unless it's because her area is as far away as possible from the home theater and maybe the home theater is pulling down the temperature in the rest of the main floor?)
posted by arniec at 9:19 AM on February 14

What furnaces do you have (size and efficiency), and how many square feet does each serve? That seems like the base information required to use a reference like this one to see if the sizing was reasonable.

Your anecdotes seem to indicate (to me) that the size is adequate to the task, but the data could take us away from opinion into a realm of professional judgment.
posted by whisk(e)y neat at 9:22 AM on February 14 [1 favorite]

A difference of about 4F from your thermostat setting when there's a -25 wind chill out? This is unlikely to be an easy fix, and probably more trouble than it's worth to continue trying.

If the walls in your grandmother's area are mostly interior walls with one exterior wall, and the theater is exterior walls on three sides, it's just going to be easier to maintain constant temperatures in your grandmother's rooms. The greater the exterior exposure, the greater the temperature swings.

Options to consider: better window coverings for insulation (cellular shades are great for this), electric throw blanket for using the theater in winter, a ceiling or portable fan for summer. Windows in particular are the easiest way to lose your heat or cool, so be sure you're doing what you can with those.
posted by asperity at 9:27 AM on February 14 [12 favorites]

I'm also sympathetic to your HVAC contractor here. Unless your house is new, energy-efficient construction (think Passivhaus standards) with modern insulation and air sealing, I think this is actually a decent outcome. Houses are complicated systems and expecting less than 5° of variance at the extremes of a 100° F+ range may not be reasonable.

A couple of other questions that might put this in perspective:

1. Are the furnaces running near constantly to maintain sub-70° F temperatures?

2. If you were to set the thermostat in the main area to 79° F, would the temperature remain at 69° F?

3. Are the ambient temperatures you're reporting measured by your thermostats? (Specifically, I'd ask myself if the thermostats themselves are reaching the mid-70s before the rest of zone, cutting off the heat prematurely.)

That said, the frequent service calls you report would concern me, and if the answers to all three questions are "yes" I would suspect that poor system design could be stressing them and causing premature failure.
posted by pullayup at 9:36 AM on February 14 [3 favorites]

It really does seem like an insulation issue. You may want to get an energy audit done. They should be able to identify the cold zones in the theater and see where the cold air is coming in with precision. They probably would use infrared, negative pressure blowers, etc.

Check out this page on the website, which has links to certified "raters":
posted by odin53 at 9:39 AM on February 14 [6 favorites]

Sizing per Manual J is pretty much the industry standard for HVAC contractors and there is even some "fudge factor" built in to that. Looking at the manual J chart, the outdoor design temperature for most of Illinois ranges from 0 to -4. So, I wouldn't expect your furnace to be able to maintain perfect room temp below that range.

Manual J calculations are based on various assumptions (the "R" value of the insulation in your walls, the type of windows you have etc.) which can be very difficult for contractors to ascertain with certainty on a non-new build.
My experience has also been that with many homes with forced air heat often contractors really struggle to get duct balancing and zoning correct. You might be able to improve matters by redesigning how the home is zoned, but that could be a major undertaking depending on how the ducts are laid out.
posted by Larry David Syndrome at 9:39 AM on February 14 [1 favorite]


The first floor is 2900sq ft.
The basement is 2100 sq ft (but has most vents closed; it's unfinished/unused)
The upstairs is 1400 sq ft.

The furnaces were installed in Nov 2014, so 5 years, 3 mos ago.

The furnace servicing the basement and first floor is Lennox EL296UH090XV36C, 96% AFUE, Upflow/Horizontal, Gas Furnace, Variable Speed, 2 Stage, 90,000 Btuh, 3 Ton, Elite Series

The furnace servicing the upstairs I couldn't find an exact model on but it was listed as 70K BTU Comfort 95% Elite Furnace - High Eff. Blower
posted by arniec at 9:41 AM on February 14

I have a sunroom on my house and it's generally a few degrees cooler in there than in the rest of the house. The windows and insulation are decent but it has three extrerior walls, it's over the unheated garage, and it's the only single-story part of the house; other rooms in my home have two exterior sides and this room has five. Home inspector, plumber (who takes care of the radiators) and energy auditor all agree: it is unrealistic to keep this room the same temp as the rest of the house (my house is single-zone). We have a space heater that looks like a woodstove that we use in there sometimes but mostly we just get under a blanket.

Is it possible to zone the home theater all to itself?
posted by mskyle at 9:51 AM on February 14 [2 favorites]

Is it normal for a furnace to not maintain a temperature during extreme heat/cold days?

In my experience, in a slightly leaky older house, it totally is normal within the range you're discussing.
posted by warriorqueen at 10:28 AM on February 14 [3 favorites]

Some anecdotal information from my recent experience with getting HVAC quotes to replace a gas furnace and AC.

Current furnace is 120,000 BTU and our house ~2000sf.

Both companies I've spoken to so far have said that that is oversized for a 2000sf house and it's more appropriate for ~4000sf house and recommend replacing with a 60-80,000BTU furnace with a 3 ton for AC.

I guess my thought is that if you have ~5000sf between your basement and first floor then maybe the 90,000BTU system is undersized?

For reference I'm in the northeast US so we don't quite get down to -7 degrees very often but even in the single digits I rarely have to set the thermostat higher than 72 or 73 to be comfortable in the house.

I would say to try to get another one or two HVAC companies out to inspect your system and see what they say. I understand the sympathy folks are giving your current contractor and while the owner makes a good point, in the end you're the customer and you need your home to be comfortable, so if that means configuring your system for extremes then that's what you need.
posted by eatcake at 10:45 AM on February 14

Is your basement ceiling insulated?
What is the basement temperature?
Does the addition have floor insulation?
Are the ducts feeding the addition insulated or do they run through an uninsulated crawl space?
posted by JackFlash at 10:54 AM on February 14

You can get an efficiency audit from ComEd for free. I'm not sure they'd find anything new, but it's worth checking out.
posted by amtho at 10:58 AM on February 14

This ain't rocket science. There are two explanations for one part of the house being colder than another -- its losing heat faster or it is being heated slower.

The first means checking insulation for floor, ceiling, walls and windows.

The second means checking that the heating ducts to the cold room are not undersized and are not uninsulated.
posted by JackFlash at 11:05 AM on February 14 [2 favorites]

I think you need way better insulation. I'm not sure you said the size of your house, but it occasionally gets super cold even though I live in a generally warm state and my heater works to maintain the house temp just fine, as does the A/C. Mine can easily maintain about 75F+ (any hotter than 72F on forced air and I am sweating) on a 0F day.

You can also check the temperature of the heat blowing from the vent while the furnace is on with an infrared gun. That's basically the hottest it will get.
posted by The_Vegetables at 11:23 AM on February 14 [1 favorite]

I took the briefest glance at Manual J and it seems kinda basic for a heat loss / heat gain calculation tbh. But America I guess. I suspect the problem is that your heat loss /heat gain numbers are off by enough for this to cause you problems maintaining setpoint temp for certain parts of the house with the equipment that was spec'd based on those flawed numbers. I'd try to find an HVAC contractor who does design work and who specifically uses a better methodology for heatloss/heat gain calculation.. also might want to do a depressurization test.... ASHRAE very likely has some certifications they give out for these types of things..
posted by some loser at 11:24 AM on February 14

I'm an engineer with some experience with HVAC and duty cycle type considerations and nothing your contractor says is out of bounds. I can't speak to the validity of his statements but the veracity seems spot on.

The other folks in this thread who are speaking to insulation and envelope testing are spot on as well. That's the low hanging fruit generally in things like this and your contractor mentions it in passing as well when they speak to the problem being focused on extreme weather days.

Now, all that said, you should not be having issues with thermostats breaking and other aspects of your system becoming physically incapacitated. Sure, stuff like that happens but if I went through more than one thermostat in a 5 or 10 year period I'd be looking into the general wiring health of my home and/or talking about it in depth with my HVAC person.

Finally, and to be clear, I don't think you can say "they sold me an undersized furnace" when you're talking about a four degree difference from your target temperature in two out of three zones of the house (with the third zone being spot on the money) when it's a -27 degree windchill outside.

Again, I'm not from north of the arctic circle but that sounds like a pretty cold day and you might, and I'm not being exact but I'm not joking either, have to have a system that's 150% or 200% larger to GUARANTEE that you won't have those deficiencies on those bitterly cold days. That's simply how heat transfer math works when you increase the delta across an insulating medium. If your contractor would have quoted you a price that was twice as much as other quotes, which I'm assuming you got when you had the system installed, would you have went with it or believed him/her when they said it was to provide iron-clad assurance that the coldest days wouldn't allow the system to vary by more than 0.5 degrees? I'm guessing you would have assumed they were trying to scam you, and you wouldn't have necessarily been wrong.
posted by RolandOfEld at 11:48 AM on February 14 [5 favorites]

Ice build up in the exhaust pipe means it was installed slightly wrong. My install got dinged on humidity running back into the system, which can cause premature failures. It's a really basic code thing and fixing it and hanging my furnace was like an extra $250.
posted by The_Vegetables at 12:46 PM on February 14 [2 favorites]

I think it is reasonable to run a space heater or some other local heating source to even out temperatures in even a new house.
posted by any portmanteau in a storm at 12:55 PM on February 14

Before the new furnace the theater would regularly drop to 50-60 degrees in the winter, and be over 95 in the summer

Your theatre room is not well insulated enough to cope with the extremes of cold/heat you're seeing.

That's it.

Frankly, maybe it's ok to put a jumper on indoors on the coldest days of the year? I run our house at 66-68 °F - that's a perfectly normal temperature for humans to be at if you actually wear clothes. (Older people usually want it a little warmer if possible.)

Switches have gone out on the furnace, we had to have our thermostats replaced twice, and we've had the furnace die in the middle of the night three times (due to the aforementioned switch issue and, they claim, ice build-up in the exhaust pipe).

This is a bit weird & suggests 1) an electrical fault somewhere and 2) that you need to insulate your exhast pipe better (presumably this is a condensing gas furnace?)
posted by pharm at 1:08 PM on February 14 [1 favorite]

Ice build up in the exhaust pipe means it was installed slightly wrong. My install got dinged on humidity running back into the system, which can cause premature failures.

The exhaust pipe is supposed to drain back into the furnace. That is what keeps ice from forming at the exit from the house. The slope should be at least 1/4 inch per foot down toward the furnace.

A high efficiency furnace condenses water from the exhaust, collects it in the furnace and then it drains by gravity or a pump into an available sewer drain.
posted by JackFlash at 2:45 PM on February 14 [1 favorite]

Is your furnace running all the time and not able to keep up or is it not kicking in when the temperature drops? the first is an insulation/ under powered/ heat loss issue. The second means you need more sensors in your large downstairs to keep the furnace better informed of the temperature throughout the space.
posted by fshgrl at 3:56 PM on February 14

This is random, but what about planting some big shrubs or something around the theater part of the house? Something to cut the wind in the winter and provide shade in the summer.
posted by bink at 4:45 PM on February 14

I'm going to buck the insufficient insulation trend here and ask if maybe you don't have adequate cold air return from your theatre. I can't give you a formula, but I'd ask someone who could.
posted by kate4914 at 5:47 PM on February 14 [2 favorites]

I'm no expert so take this with a grain of salt, but I have hotter/cooler areas in my house (not extremes) and I feel they are due to the fact that the sensor for the one thermostat is in the center of the house, not near any windows or doors, so the thermostat thinks it's "nice and comfy" or "at the correct temperature" when if you're in the bedroom, living room, or office (all rooms with exterior walls), it's cooler.

I've often wondered if there's a way to have multiple sensors and average them as the input to the thermostat, but the differences in the rooms aren't worth the cost of trying to do that for us.
posted by TimHare at 7:24 PM on February 15

(TimHare, we have an Ecobee thermostat and you can buy as many sensors as you want and do just what you suggest. You can even turn off the sensor at the thermostat itself and just use the other sensor(s) if it is installed in a stupid place and not worth moving.)
posted by misskaz at 9:45 AM on February 16

OP, I realize my earlier reply seemed very extreme and it turns out putting in a less dense air filter improved our air flow and the temp of the house considerably. So another thing to check is to make sure you're not using the Ultra-Super-Max air filter and go with something that doesn't impede air flow quite so much.
posted by misskaz at 9:46 AM on February 16

Extra sensors aren't going to improve the root problem, uneven heating. All an extra sensor is going to do is cause the furnace to run longer, which you can accomplish just as easily by turning up the main thermostat a couple of degrees. An extra sensor doesn't cause more heat to flow to the cold room. It just heats up the whole house.
posted by JackFlash at 10:05 AM on February 16

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