We Built a DIY Woodstove Water Heater for Indoor Wood-Heated Water

Ditch nonrenewable water-heating systems and let your woodstove do the work instead.

Reader Contribution by Kyle Chandler-Isacksen
Published on February 12, 2021
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by Kyle Isacksen
The author’s woodstove is plumbed to a recycled water heater that sits above the stove, allowing the thermosiphon effect to circulate water between them.

For years, we’ve been experimenting with different ways to heat water using our woodburning stove. Initially, we had a small woodstove into which I plumbed a copper pipe from an old metal mortar box that I bought at an Army surplus store. It held about 8 gallons of water and worked great as a stand-alone system for baths for our young children, and it provided enough water to pour over ourselves during a shower. After we built our mini-masonry heater, we switched to heating water in big pots on our large cooktop, and we put the hot water into a watering can mounted in our shower. This setup provided about 11⁄2 gallons of hot water. It worked fine for a while, but, like so many things that change as your children become teenagers, we needed an upgrade to keep hygiene and morale up on our urban homestead.

While visiting some friends who’ve been living off-grid for decades, I noticed their woodstove thermosiphon water-heating system. It was something I’d learned about several years ago, but I’d never seen one firsthand. Being able to see a system and talk about its functionality with its users makes a huge difference in whether or not I’ll tackle a project — especially one that involves plumbing and heat. After I’d discussed the project details with my friends, I felt confident trying it myself.

Assembling the System

t connector added to a blue handled drain valve

Similar to our outdoor solar shower, this system takes advantage of the thermosiphon effect, in which cold water starts at a low point and then gets heated, which causes it to rise, creating a circular flow without any pumps or pressurized water.

I started by getting a used 30-gallon water heater from my neighbor. It’s old but leak-free. Used water heaters for this type of project are typically easy enough to find. As long as they don’t leak, it doesn’t matter if the heating element has gone out. The one I found happened to be for propane, but I’ve used old electric and natural gas water heaters before too. I then built a raised platform in our water heater closet so the tank sits higher than our stove. Placing it above the stove was essential, because it won’t work well if the tank isn’t higher than the heat source. Fortunately, that closet is just a couple of feet from our stove. From there, it was just a matter of plumbing the tank.

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