Does a heat pump water heater in upstate NY make sense?

Question

I currently have a 17-year-old, gas water heater. It's not giving me a problem yet, but I'm getting nervous about it and investigating replacing it. I am trying to be both economic and reduce my reliance on fossil fuels, and HPWHs look like they might be a good option.

For some reason, the current WH is about as far away from the faucets as possible in my 1940's house, but by eliminating fume exhaust needs with a HPWH, I can relocated it to directly below the lines to the bathrooms and next to the kitchen. Luckily, that is also where the drain (for condensate) is too.

I have the skill/knowledge to install one from a big-box store myself, but I'm not sure I trust the quality. Although more expensive, I'd prefer to have a professional installation with warranty assurance and some authority with the manufacturer.

However, the plumbers I've reached out to for quotes have been discouraging of HPWHs in favor of just replacing with gas. I live in upstate NY, so I realize that the efficiency in my 60-degree basement won't be as good as a 85-degree garage in the south, but I thought it was still an economical choice over the lifetime of the unit -- especially if I run it in heat-pump mode only without the direct heater element.

Am I incorrect and a HPWH as a replacement for gas (rather than part of a high-efficiency new-home build) doesn't make sense in upstate NY? Are the plumbers just not familiar with HPWHs? (I saw somewhere that they are still only a couple percent of all new installs.)

Thanks!

Answer 1

The plumbers don't like complications.

The complication with a heat pump water heater at least, the single-unit ones, is that they are an air conditioner for the room. They are stealing heat from the room they're in. So the problem isn't that your basement is 60 degrees. The problem is that it will be much colder when the HPWH is going to town! You say "it'll come from the earth" but you might want to fact-check that belief. You're talking about a fair number of BTUs. Putting a 100 degree rise on a 30 gallon tank (250 pounds) is 25,000 BTUs.

Now you're thinking "I won't need that dehumidifier anymore". But let's think about latent heat, or the heat contained in the water vapor by virtue of it being vapor which is 1000 BTU per pound. When the dehumidifier condenses a pound (pint) of water, it adds 1000 BTU of heat into the room, because that is the latent heat of vaporization of water. That had to go somewhere, and it's not in the water vapor anymore - it's in the room now. Assuming it's working at 4 COP, it also adds 250 BTU of heat from its own mechanical function.

One reason the basement is 60 degrees (and not colder) is that 1250 BTU added to the room per pound of water condensed. You're going to lose that. Those BTU will now go into the hot water tank. In a 30 gallon (250 pound) tank, that 1250 BTU will raise the water in the tank 5 degrees F.

So yes, I am concerned about basement temperature, and I think your assumptions of "it's 60F because it's in contact with the earth" may be incorrect.

Now, a much more difficult thing to find, but certainly solves this problem, is a "mini-split" heat pump which has (as one of its heads) a water tank. Now, the heat pump lives outside and is taking heat from ambient outside air. If you think heat pumps don't work that cold, you're thinking of decrepit old American tech. Others have lapped us with new technologies using new refrigerants, that work just fine and sustain 2.5+ COP down to Chicago cold. That's why so many buildings in Ukraine have mini-splits on them.

If you're wondering how heat pumps can work that cold, think in Kelvin. It is numbered from absolute zero, which is what REAL cold is. -10°F is actually 250K and we enjoy home temperatures of 295K. Water tanks are best kept at 333K.

Answer 2

If you heat the house with gas or wood (seems likely in upstate NY if you have gas for the water heater now) it can make sense - just be sure to provide enough heat to the room where the HPWH (or its remote intake duct, which is a way to improve that) lives, since in winter you're heating water with gas via the heat pump - while in summer you get the benefit of free air conditioning/dehumidification and don't use gas for heating water. And, in your case, you get to put the heater where you need it for most efficient hot water distribution, which is a big win.

My personal experience with getting a professional installation quote (required for my local "rebate" program, making it a bad joke) was that professional installation and overly-marked-up-via-the-professional exactly-the-same-water-heater-as-a-big-box more than exceeded the price of buying two from a big box, even after the alleged rebate.

So, I'd go with the self-install option in your shoes.

However, since I heat with heat pumps, and will eventually add a wood boiler to that, I went with a plain old electric at 1/3 the price and less to go wrong with it, since it would be loading my heating heat pumps during their difficult season, and I really don't need AC 99% of the time. When I get the wood boiler rigged, that can heat the electric tank mostly. I'll revisit that in a decade or so when that one is due for replacement. My only gas option is propane which has been crazy expensive for years now in my area.

You might also look at your relative gas and electric rates, factoring in the coefficient of performance of the heat pump on the electric rates.

The math can also change if you are planning to add solar PV panels.