Are air heat pumps effective on very cold or very hot days

there are heat pumps that are capable to -15*F and lower. Are they economical, practical, comfortable I don’t think so. I still prefer hot water or steam over heat pumps when that NE Wind is blowing!

Yes, they can. They work down to -15F or so. And for cooling, work the same as an air conditioner (they’re mechanically almost identical). They, like ACs, lose efficiency as it gets hotter.

For heating, they can easily outperform fossil fueled boilers on cost, but costs everywhere are different and change constantly, so your situation will of course be different than others.

My own experience — northwest Connecticut — is that they work as well as a good air conditioner in the summer, and they work nicely for winter heat — down to perhaps 20 or so. Below that, dear old Cedric's steam heat is cheaper and simpler..

Can you clarify if you were trying to keep your house at 68 to 72F with an outside temperature approaching 100°?

If that is the case, it can be a challenge for your HVAC system depending on the size of the unit and tightness of envelope

On hot days it’s not essential to hit a specific number to achieve comfort. Lowering the inside temperature by 15-20 degrees and lowering relative humidity to 45-55% range will often yield a comfortable environment without over taxing your HVAC.

You can look up the heating and cooling design temperatures for your county here: https://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/County%20Level%20Design%20Temperature%20Reference%20Guide%20-%202015-06-24.pdf

There is a non-profit called NEEP.org — the Northeast Energy Efficiency Partnership — that performs testing of the cold weather performance of heat pumps. At their website, https://ashp.neep.org/, they have a database of the cold-weather performance of over 100,000 tested configurations.

"Upstate New York" is a huge geographic area. If you're in Erie County, the heating design temperature is 7F. At 5F, a Mitsubishi M-Series produces 94% of its production at 47F. So it should have no problem keeping up if it's properly sized. If you're in Essex County where the design temperature is -11F you might have a little more trouble.

At 5F, the COP is 1.93.

Here's the NEEP page for the M-series.

https://ashp.neep.org/#!/product/34583/7/25000/95/7500/0///0

What exactly is meant by "Over taxing" ?

To me, a system running non-stop is actually better for it than cycling.

Air to air heat pumps blow luke warm air in cold outdoor conditions from my experience, not the most comfortable heat, especially for older folks.i

compressors don’t die from running, there murdered by excessive superheat, excessive head pressure and excessive or too low superheat and excessive start stop cycles!

@GeneSh , what are you using for heat now?

Going to a heat pump will be fine IMO, as long as it's not your only heat source. If you plan on eliminating the "fossil fuel" boiler or furnace, then you'll need electric resistance heat for when the heat pump doesn't heat… or pump. And for when the outdoor unit goes into defrost. Parts aren't always on the truck. Especially those defrost boards.

With my own situation, I have and oil fired boiler with fin tube baseboard and one radiant zone. If (when) either the X13 blower motor or compressor goes, I'm going to install a 2 stage heat pump. Not communicating. Not an inverter system. 2 stage. Simple. More common parts availability. The 3rd stage will be the boiler and for defrost.

Whatever you do, vet the contractor, and make sure they do the math to size the system and the ductwork correctly.

@ChrisJ

"It's actually amazing how many hours a compressor can last when treated correctly." Isn't that the truth.

It's amazing the beating they can take.

People who say they "go bad" for no reason are wrong. You can always have a lemon but if they get reasonable maintenance. they will run for a long time.

In the Northeast if you study heat loss and heat gain calculations. You will find that in most but certainly not all cases the cooling load is half the heating load. Where I am we design for 0 deg. which is fine for MA & CT but NH, VT & Maine would need more heat.

With that being said what @SuperTech posted is exactly correct. If you have a building that needs 3 tons of cooling and you install a heat pump your capacity will be 36,000 btu on cooling and about (36000 x 1.3) or 46,000 btu on heat due to the heat of rejection.

If the cooling load is 1/2 the heating load which is common, you have to do as @SuperTech mentioned oversize the heat which will make the cooling suffer.

R32 invertor systems change this conversation. They have significant performance improvements over R410A at extreme temps.

Doesn't change the fact that hydronic heating is much more comfortable in nearly all cases.

At NEEP.org there is a thing called the "Advanced Sizing Tool."

Pick a heat pump, put in your zip code and your heating and cooling loads. It gives you a report like this:

There's no need to guess.