Venting indoor sauna to closet housing heat pump water heater
I’m replacing the old water heater in my new house. We’re a family of two. With the purchase of new appliances and internal water heaters, the hot water heater will heat the water coming out of the shower and sinks only. I’d still like to consider getting a heat pump water heater. However, it’s a small house on a pier and beam foundation with crawlspace and no garage. If I put the water heater in a newly build closet (about 5 feet from it’s current location under a cabinet) and put a small, indoor sauna beside it (currently in the plans), can I vent the sauna into that closet – warmer air goes into the 2×2 closet and cooler air goes back into the sauna. Anyone see problems with this configuration?
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Most heat pump water heaters need way more space than a 2x2 closet. Most units need around 750-1000 cubic feet. There are hpwh that place the compressor outside, like a minisplit. They're pricey, though.
For a steam sauna: It will never work.
For a dry sauna: It might work, but it almost certainly isn't worth it. You'll need to duct your HPWH into the sauna (see: https://www.greenbuildingadvisor.com/article/attaching-ducts-heat-pump-water-heater). The sauna would need to be big (generally 750-1000 cubic feet as Stephen says). You might be able to get away with a smaller sauna if it was connected to a big room, and you always leave the doors open when it is not in use.
And if you meet all of those requirements, the gains are really minimal. You use a sauna, what, a couple of hours a week? That's about 1% of the time the hot water heater is in use. Overall, you'd be boosting your average efficiency by a fraction of a percent, unless you are using the sauna for several hours every day.
How big is the sauna room? If the sauna room is big enough to support the water heater it can potentially work ducting the water heater to the sauna.
What is your local DOE climate zone? In a sufficiently warm climate ducting the water heater to the outdoors can work pretty well (although climates where it works efficiently with outdor air aren't where people usually build saunas.)
How tall is the crawlspace? Is the crawlspace vented to the outdoors?
Thanks, all. I'm near Annapolis, MD. Dry sauna will be small, 3'x4'. It will open in the shower area of the bathroom, which opens into the toilet/sink area. Crawlspace is about 2' high, currently open to the elements. I have a small room off the house for the well tank, but it does get cold here.
I can always get a regular 50 gallon or less tank.
>... near Annapolis, MD. Dry sauna will be small, 3'x4'...
Too small, too cold in winter for tank-top type heat pump water heaters.
>Crawlspace is about 2' high, currently open to the elements.
Too cold in winter unless there is an insulated skirt around the perimeter.
For about four grand you can get a CO2-refrigerant heat pump water heater with the heat pump outdoors:
https://foursevenfive.com/sanden-sanco2/
https://worldclasssupply.com/store/Sanden-Generation-3-Heat-Pump-Water-Heater.html
https://www.sandenwaterheater.com/sanden/assets/File/Sanden_40950-44672_owners-manual.pdf
The 43 gallon version is big enough for two people, even if kept at 125-130F (for efficiency) instead of the maximum 175F. The upcharge for the 83 gallon isn't much though. The taller skinnier version of the Sanden 43 gallon tank is 22.5" in diameter.
Fitting a 50 gallon electric into a 2' x 2' closet takes a lot of grease and sometimes a big hammer. Tank diameters are in the 22-26" range for most standard electric water heaters, and that's not counting the drain valve or heater element doors, pressure & temperature valve, etc. If the closet isn't framed-in yet go for at least 30" x 30". If it's already built, measure the closed carefully, and read the specified dimensions carefully.
Thanks Dana. I can make the closet larger. I'll also get a regular water heater since my single creative solution to recreate the necessary elements won't work.