My Heat Pump Water Heater Provides Free AC – CleanTechnica

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What does your water heater emit as a waste product? Gross NOx pollution that goes up your flue vent? My water heater creates cool, filtered air, essentially free air conditioning that cools my house on the scorching, 100 degree, climate change hot days. It’s an amazing byproduct that most people probably don’t know about, but one that I’ve learned to harness recently to help cool my home for free in the summer.

This free AC comes from our heat pump water heater (HPWH). We’ve actually installed four of them, one in our home, one in an accessory dwelling unit, and two in a duplex rental property. Heat pump water heaters work by pulling heat from the surrounding air and transferring it into a water tank. This process means that they exhaust only cool air, no gas, no pollution, just cool air (like an air conditioner).

In fact you could think of a heat pump water heater as an AC system, but instead of exhausting that waste heat outside like ACs do, a HPWH uses the waste heat to heat water. This makes HPWHs extremely efficient — for every unit of energy you use, you get four units of heat out of it. It’s also why HPWHs cost so little to run — typically between $100-$150 a year in electricity costs to heat all the water your family needs.

But even though we’ve been enjoying the extremely low utility bills and lots of hot water from our heat pump water heater for 8 years now, we’ve never quite mastered the art of harnessing a HPWH’s cool air in the summer until this year. That’s because for the first six plus years we owned our HPWH, we ducted its air out of our house.

But after a home renovation last year, we decided to remove the ducts and have the water heater pull heat from and exhaust cool air into the house.

Now, in the winter we do pay a penalty for this because the water heater is pulling warm air from your home to heat the water that has to be made up for by your heating system (in my case, ductless heat pumps). Over the years some CleanTechnica readers have mentioned in the comments to some of my articles that this is a large penalty. It’s not. Our home still uses an insanely low amount of energy (1/5 the national average) and my space heating is provided by highly efficient heat pumps. So cool air in the winter is not a big deal.

And in the summer we now get this free, delicious, air conditioning. What’s more, I’m able to do a couple tricks to run the water heater during the hottest part of the day and give me the AC exactly when I want it.

Here’s what I’ve been doing. On hot days at around noon or one PM, I’ve been turning our HPWH from 120 to 140°. You can do this with the buttons on the water heater or with the app. Heating water to this higher temperature turns on the heat pumps which will run for 3 to 4 hours during the time when my solar panels are cranking out electricity. Now as a disclaimer, all of our faucets have built-in anti-scald devices which protect us from the hot 140° water. You should make sure you have the same if you try this.

During the time it’s running, the heat pump water heater puts out as much cooling as a small window air conditioner (.35 tons for the HPWH vs .4 tons for a small window AC). Running my HPWH during the hot hours is thus like running a small window AC unit and not paying for the electricity. Pretty nifty!

Once my water heater has reached 140°, my living room and kitchen are usually several degrees cooler and I then turn my HPWH back down to 120°. The extra hot water will be used to run the dishwasher and any evening showers and the HPWH probably won’t turn on again until the next day when we use it for more free cooling.

Now, our home is one of the 26% of homes nationally where the water heater is located within the building envelope — in a utility closet. Most water heaters are located in basements or garages where you would need to duct it to take advantage of that free AC or you might not bother. But, if your water heater is located indoors you can easily harness the free summertime cooling, all the while heating your water super efficiently on solar power (if you have panels like we do). Yet another reason to love HPWHs.

Oh, and make sure to get yours before the 30% tax credit expires at the end of the year!