Use Your Wood Stove as a Water Heater

Your wood stove can heat more than your home. This hot water heating system uses extra heat to produce hot water that will stay warm up to 48 hours!

| November/December 1976

Three years ago, we were sitting in our cabins wondering how we could satisfy our addictions for hot baths and showers, without paying ridiculous prices for disappearing reserves of fossil fuels. Putting our talents together (one of us is a mechanical wizard and the other a Ph.D. chemist), we devised a homestead alternate energy system — based on the use of otherwise-wasted stovepipe heat — that's allowed us to take those hot baths. We call our system the Blazing Showers Stovepipe Hot Water Heater.

Hot Water Basics

As you can see in Fig. 1 (see Image Gallery), an ordinary water heater is nothing more than a storage tank (located between a house's water source and its various hot water faucets) sitting over a gas or electric burner. Since water tends to rise as it's heated, cold water is piped in at the bottom of the tank, while hot water is drawn off from the top.

Fig. 2 compares such a conventional water heater with a Blazing Showers system. As you can see, our setup employs a coil of copper tubing — located inside a wood burning stove's stovepipe — to heat the water that's held in our storage tank. Hot smoke rising through the stovepipe warms the water in the copper coil, which causes it to rise (and thereby draw more cold water into the coil). Meanwhile, the stovepipe-heated water flows into the top of the storage tank, where it remains until someone decides to take a "blazing shower" and turns on a faucet.

Notice that there are no pumps in our system: Instead, plain ole thermal convection does all the work.

Hot Water... Overnight!

How long does it take to fill a tank with hot water this way? The answer depends on how cold the incoming cold water is, how many gallons your water heater holds, and how hot the flame is in your stove. We estimate that a blazing fire in an average-sized wood-burner can produce 20 gallons of hot water per hour. And—if you store that heated water in an insulated tank as we prescribe—it'll remain hot for up to 48 hours after the fire goes out. What this means in practical terms is that if you have a fire in your stove one evening, you'll still have all the hot water you want (for bathing, dishwashing, etc.) the following morning when you wake up. In fact, that water will actually remain warm for two full days ... even if you don't light the stove again at any time during that period.

First Things First: Storage Tank

The first thing you need before you can install a system of your own, of course, is a storage tank. If you already have a hot water heater, you can use it ... otherwise, look around for a "previously owned" unit.

11/15/2017 7:31:53 AM

I think this is amazing work. But ... there is always a but, no? I live in small house in a city that I heat with natural gas, forced air. Heating with wood isn't really an option for this house but I want to find ways to heat water that are less fuel dependent. If I had a gas stove (you know the kind that look like a wood stove) do you think your ideas could be incorporated? If I could do that without using more gas I would save more than the $25 you're talking about - my water heating costs about $45 a month!

10/31/2017 4:04:27 PM

We are off-grid but not highly mechanical, though we aren't doing a bad job at it. I love the idea of heating water with the wood stove but have one point where I don't understand the process clearly from your diagram. I see that the heated air can become trapped on rising and going into the water tank, but what do you actually do about it, what is the item you mention and where do you put it? My artist/writer brain needs a very simple diagram/instructions for that!

10/31/2017 4:04:25 PM

I love the idea of using the woodstove to heat water and being off-grid, it would be especially useful to us in the winter. We are doing pretty well in our situation though we are neither of us highly mechanical which makes even the simple diagrams like these an effort for our brains! However, I can understand the mechanics of how it works, though I don't understand what we would actually do to prevent the trapped air you mention as the hot water goes into the tank. What is the part you have invented, where and how is it attached? I'm an artist, writer and singer, and the only-slightly-mechanical part of my brain lost it at that point!

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