Replacing a Tankless Water Heater With a Heat-Pump Water Heater
For many reasons, probably shared by many people on this website, I don’t like combusting fossil fuels — especially not in my house. Currently I’ve got a natural gas stove, natural gas furnace (crawl space), and natural gas tankless water heater (attic).
Easy enough to replace the stove with induction, and to replace the furnace with a heat pump at some point (climate zone 4a, so a decent heat pump would work fine).
The one I’m struggling with is the water heater. Would I be totally crazy to replace a tankless unit in my attic with a tank heat pump unit? Does the risk of a leaky tank and water damage outweigh the benefit of eliminating fossil fuel combustion in my house?
Just curious to hear how other like-minded folks would evaluate this issue. The attic is a walk-up attic so it could support the weight of a tank water heater. I’ve also already got 240v electric service up there, so it would be easy to connect. Moving the water heater to a different location isn’t a great idea because then it would take a really long time for hot water to get to my upstairs bathrooms! Plus, my attic is sealed with spray foam, so the attic would benefit from the cooling/dehumidification of a heat pump water heater. Finally, electricity isn’t terribly expensive in my area (about 11 cent/kWh). I’m not sure whether operating a heat pump water heater would be cheaper than the NG tankless, but I think any difference would be pretty minimal, and if operating cost were the only consideration, I’d happily pay a bit more per year in operating costs to get rid of another fossil fuel burning appliance.
Thanks for any insight.
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I like my 80 gallon Raheem, but I not sure I would want it in the attic. I’m not that concerned about leaking, but I could envision weight and noise being deal breakers.
Noise? I assume that's the compressor noise? My master bedroom is actually directly beneath where the water heater would be. Do you think it's loud enough to travel through a floor as anything more than a light hum?
Are you certain you have the room to install the required capacity?
I wouldn't do it especially if it were possible to finish the attic.
I'm certain. Part of the attic is already finished. The remaining unfinished part is a "utility" room that also houses a heat pump air handler. So it will never get finished.
Space is not an issue at all.
Ahh ok. From my own anecdotal experience I'm not a fan of having the water heater on an upper floor. My current water heater is in a hallway closet on the second floor so even though I don't like it, I would hope that I would become aware of a pending failure. If it's on the third floor it's more out-of-sight - out-of-mind no?
Exactly, which is why I'm a little concerned about a leak. I do have an alarm system that has leak detectors that work pretty well. I suppose I could put one in the pan and that would pretty reliably notify me of any leak. As long as the leak is minor and not some sort of catastrophic tank failure, I could probably get things fixed before any real water damage.
The newest Rheem's have a "leak guard" feature that is supposed to limit water leaks to 20 ounces.
Just as an FYI. Most of the posts I've read advise going with the biggest tank you can afford. I put in the 80 gallon since it wasn't much of an up-charge over the 60 gallon. If you go with one of big units, keep in mind may weigh in at around 1,000 pounds.
Is the attic within the thermal envelope? To me it's a no go if unconditioned attic
Noise I hear with mine is more fan noise not compressor. Mine right below my bathroom on cement floor. There could be vibration issues being on wood floored attic.
Entire attic envelope is sealed with spray foam. So I'd benefit from the cooling/dehumidification from about May through October in my climate zone.
So yours is a floor below a bathroom? And you can hear it in the bathroom?
Yes, it is in my mechanical room just below the bathroom.
There is only 3/4" subfloor, 3/8" plywood and vinyl floor between the rooms. Like someone else said it sound like a dehumidifier running.
My HPHW heater is an almost 7 yr old GE Geospring.
My Rheem is in the garage behind 5/8 inch drywall, 3.5 inches of open cell foam, and another layer of 5/8 inch drywall. If I walk by that area when the tank is running, I can just hear the machine noise. But it is sitting on a concrete slab.
If you have a portable dehumidifier, place it where you are planning to install the water heater. If that amount of noise and vibration bothers you, the HPWH would probably as well.
FYI. I had a Rheem Marathon electric water heater in my last house. It was great--and dead quiet since there is no compressor.
Thanks, Steve. So the Rheem is roughly comparable in noise/vibration to a portable dehumidifier? That sounds like a good way to get an estimate.
For me it's either a hybrid heat pump or keeping the NG tankless that's already up there. The energy efficiency hit of going from NG tankless to electric resistance would just be too much for me to handle, even if it did allow me to eliminate a gas appliance.
Just to clarify, Rheem says its HPWH produces 49 db when operating. A dehumidifier set to low might produce 59 db or more (based on http://www.dehumidifierbuyersguide.com/noise-output/). So a dehumidifier is probably at least 10 times as loud. I should have been more detailed in my answer. But if you test with a dehumidifier and the sound and vibration are not an issue, I doubt the HPWH would be noticed.
Ah, the dB number is helpful. I found the dB specs for a dehumidifier I have so I can test this and get a really good idea. Thanks so much.,
For a new build, I am looking at Artic heat pump that can do heating, cooling and DHW. Why not get down to one thing to maintain.
I love that concept but this is a 10 year old house. Would be prohibitively expensive and difficult to get rid of two existing HVACs and water heater to replace with a single unit that does it all.
@steveknapp...80 gallons of water is 660lbs...is the water heater really another 340 pounds as you said 1,000 lbs total?
My fault for relying on memory. That said, a gallon weighs approximately 8.3 pounds (8.3 x 80 = 664 pounds). The 80 gallon units weighs 244 pounds according to Rheem (664 x 244 = 908). A 30" aluminum pan weighs about 3 pounds. So we are at 911 pounds approximately. If the water heater leaked (and the automatic shutoff malfunctioned), you could end up with approximately 11.66 gallons in the pan (11.66 x 8.3 = 99.77 pounds). So 908 + 3 + 100 = 1,011 pounds. Plus, a couple of hundred for whoever goes into the attic to service the unit.
Really, I am kind of kidding here. The 1,000 pounds was mostly a WAG, but I am concerned about the safety of an attic installation. It might be fine for an attic framed in dimensional lumber, but someone reading this site might have a similar space framed with trusses (like mine).
Well played. I really had no idea how heavy the water heater would be I just knew the weight of the water itself.
i have a rheem manufactured in 9/2021 and it is 60 dB at chest height a meter away and the sound is a 190 Hz tone. a friend has a GE geospring manufactured in 7/2016 and it is 50 dB and white noise. we have complained up a storm about the noise and fortunately our installer is going to replace it for free with a regular electric one.
one way to check if you can handle the noise is to figure out a way to play a 190 Hz tone from a speaker and then adjust the volume until it is 60 dB as measured with your phone. then go to the living areas and see if it's bearable. i wish we had done this.