Heating a home during extremely cold weather

[BBatesokc]

Just wondering, what should a home owner's expectation be of their heating unit during really cold weather like we are getting now?

Or, in other words, how much warmer than the outside temps should you be able to keep your house without the heating unit running non-stop 24/7?

I know there are several variables (house size, heating unit size, insulation, etc.) but when it's 4-degrees outside and you set your thermostat at say 67, is it reasonable to expect your heating unit to be able to keep your house at that temp without running 24/7 non-stop? Actually, our's is running continuously now and only maintaining about 64.5 degrees (2,400 sq feet, two stories).

We have a heat pump (which may be the biggest reason it's working harder in these temps)

[Thomas Vu]

I don't know much about it, and my 2 cents is poor insulation.

[mkjeeves]

I'm not an HVAC professional but here's what I understand...systems are supposed to take into account heat loss, air infiltration for the house construction and be sized to maintain a house at 70 degrees when the outside temperture is at the design temperture for the location. For Oklahoma City, that is 13F at the low end, 97 at the high end. If the designer hits the calculation of heating loss and furnace size required right on the money for the minimum size, it could run continuously when it's 13F outside to keep your house at 70F inside. If larger than required it will run less often but if too oversized, it will cycle too frequently in milder temperaturers and be less efficient than if sized correctly. I think that also means when it's 5F outside you might only be able to maintain 62F inside.

I have two systems in my house with overlapping coverage. The one in the part of the house with lots of large windows and the most heat loss seems to run about 80% of the time in this weather to keep our house around 74F. I'm interested in seeing the data for both systems when/if it populates on the ecobee smart thermostat website.

[BBatesokc]

I don't know much about it, and my 2 cents is poor insulation.

Doubt it's "poor insulation." We had the house audited for energy efficiency when we bought it. It scored really high with the only real issues being more insulation needed over the garage and two exterior doors that were not sealing and allowed outside air to flow in. Both issues were fixed. Rock house with really nice double hung windows throughout.

For Oklahoma City, that is 13F at the low end, 97 at the high end. If the designer hits the calculation of heating loss and furnace size required right on the money for the minimum size, it could run continuously when it's 13F outside to keep your house at 70F inside. If larger than required it will run less often but if too oversized, it will cycle too frequently in milder temperaturers and be less efficient than if sized correctly. I think that also means when it's 5F outside you might only be able to maintain 62F inside.

Hope that's it. I've been told before to only expect so many degrees above the outside temp, just couldn't remember the number. Got the fireplace going this morning and the heater finally stopped for now. I show the temp outside to be only 6-degrees above. So, I can't image being able to easily keep the house at 67-70.

[jerrywall]

My house is almost 20 years old, but I did replace the heater two years ago. We haven't dropped below 67, although the heater is running pretty continuously. On the other hand, I haven't done the weather stripping and insulation on the windows I need to.

[rezman]

BBates, is your system heat pump only or is it dual fuel?. I know heat pumps by themselves only work well down to certain temps like 28 - 30 degrees. So on dual fuel system, below those temps the gas furnace side kicks in and it operates as actual furnace. We have a conventional system on a single story house, and right now, set at 71 degrees, the furnace kicks in and out at what I believe to be reasonable cycles.

I do know that one thing that can affect the the operation is location of the thermostat. In some houses they’re not
placed in the best location for best performance.

[BBatesokc]

Called a heat and air friend and he said that's the trade off with my energy efficient heat pump. Very efficient and works well - until temperatures become abnormally extreme.

[Bill Robertson]

Ours is keeping the house @ 71 and running maybe 20 to 25% of the time. House built in 1885. New heating system in 2016. 1500 sq ft. house and I keep the two car garage at 55 with a wall mounted heater. Our gas bill is averaged and runs $46 a month.

[mkjeeves]

Called a heat and air friend and he said that's the trade off with my energy efficient heat pump. Very efficient and works well - until temperatures become abnormally extreme.

There's a point where the heat pump part shuts down and switches over to electric heat strips.

This is the runtime graph with outside temp on one of my units for December. The other one is similar. It's the first time I've gotten a report since I installed the Ecobee sensors. Black is the average outside temp. Orange is hours the unit ran in heat mode each day, so maybe 70% of the time yesterday.

[u50254082]

If you ONLY have a heat pump then I'm surprised you were able to maintain 65 indoors. As you mentioned, though, the unit was running 100% of the time so there is a negative situation where you are spending money on electricity every minute but not gaining a lot of indoor comfort as a result. Some of the fancier Mitsubishi or Fujitsu heat pumps can squeeze out a lot more heat down to 0*F but those aren't likely to be common in OK.

So the unit does not have a backup heat source like electric strips or gas?

[bombermwc]

Ive got a 2k ft house and a 17 year old furnace (house built in '95). We keep the house at 71 and it only runs once or twice an hour for a few minutes at a time.

We had an issue where it was running constantly and found out that we had a dirty flame sensor, but it was an obvious problem because the air coming from the vents wasn't warm like it should be.

So if you think there's an issue like that, then it probably would be worth having someone give it a tune-up.

[BBatesokc]

Think I figured it out (based on comments above). When we moved into our house it had a newer thermostat installed but that thermostat did not have a 'back up heat' option. Apparently the original did, but the owners replaced it prior to putting the house up for sale because it was very old (but, they kept it and i found it in a box in the attic). We replaced that thermostat with a wifi one and since the one we replaced didn't have a back-up hat option we didn't look for that on the new one. Replacing the thermostat and hope that fixes the problem (fingers crossed).

[Zuplar]

Hopefully that solves your issue. If so simple enough.

[BLJR]

Bbates, sounds like you have figured this out since original post. the one thing I have noticed that can be a major game changer is the cocking around the windows. Our house is only 3 years old now, but every house I have ever lived in (new or old) gets small cracks around the windows. Go put your hand up to them on weather like this and you will be shocked. Every October, I designate a window day and check the cocking inside and out.

[Rover]

If your system isn’t running at least 80% of the time in this weather then it is way oversized. If it runs 100% of the time and temperature keeps falling inside then it is either undersized or you have infiltration, distribution, or insulation problems.

Many inexperienced HVAC sellers/installers sell more capacity than needed because it seems safer to sell you an oversized unit than to properly calculate the size. Many are more trained on installation than designing.

The problem is usually worse on the AC side than heating.

[u50254082]

If your system isn’t running at least 80% of the time in this weather then it is way oversized. If it runs 100% of the time and temperature keeps falling inside then it is either undersized or you have infiltration, distribution, or insulation problems.

Many inexperienced HVAC sellers/installers sell more capacity than needed because it seems safer to sell you an oversized unit than to properly calculate the size. Many are more trained on installation than designing.

The problem is usually worse on the AC side than heating.

Since it sounds like you know a thing or two -- can you recommend any HVAC companies in the metro that do a proper Manual J load calc before installing a system? It seems like most of them still go by the rule of thumb that says 1 ton for every 500 sq.ft of area, but I think changes to the IRC mean homes are tighter and better insulated so the rule of thumb will always oversize.

Then again, houses keep being built with tons of useless ceiling space so that may just offset any building efficiency gains.

[BBatesokc]

Heat and air guy came out. Said there was a combination of issues..... One, it's a 95% efficient unit and he says those typically don't work as well on the rare occasions temps drop below 18 degrees. This seems to be reliable info. as during the day when temps get back up to 18 or more then the heat does cycle off more than in the middle of the night when it drops to 4 degrees.

Also, house was built in 1964 and doesn't have traditional aluminum (?) venting. It uses the space in the floor joists. Heat and air guy said he doesn't like that type of venting because you've essentially asked your carpenter to do your duct work. He said it also tends to leak - a lot over time. He went up into the attic and sealed several large leaks.

We share see.

[u50254082]

Brian you might be a good candidate for a ductless mini split someday.

[BBatesokc]

Brian you might be a good candidate for a ductless mini split someday.

We've considered that for our two large upstairs rooms.

[baralheia]

Just wondering, what should a home owner's expectation be of their heating unit during really cold weather like we are getting now?

Or, in other words, how much warmer than the outside temps should you be able to keep your house without the heating unit running non-stop 24/7?

I know there are several variables (house size, heating unit size, insulation, etc.) but when it's 4-degrees outside and you set your thermostat at say 67, is it reasonable to expect your heating unit to be able to keep your house at that temp without running 24/7 non-stop? Actually, our's is running continuously now and only maintaining about 64.5 degrees (2,400 sq feet, two stories).

We have a heat pump (which may be the biggest reason it's working harder in these temps)

I am not an HVAC professional, but it sounds like your heater may be slightly undersized for the size of your house. I have a poorly-insulated 60's ranch-style house (1400 sq. ft., single story) with the original aluminum windows that have long since lost their airtightness... and even on the coldest of the last few days, with the thermostat set to 72, our heater "only" ran for 8 3/4 hours all day according to Nest.