All domestic hot water in our home currently is heated by the wood cook stove and stored in the tank behind the stove for later use. Since we have been using the wood cook stove to heat the home and cook meals, there has been plenty of hot water for showers, dishes, and laundry during the late fall, winter, and early spring. However, in the late spring, summer, and early fall, heating the wood cook stove takes a cool house and makes it a furnace, so we had to come up with an alternative; we use a propane instant hot water heater.
When plumbing the water through the wood stove, it is important to remember you are plumbing an open loop system. Why? Because if you don’t, you are plumbing a potential explosion in your home and everyone and everything will receive hot water in an uncontrolled fashion, which is potential for a very bad day, and that is putting it mildly; it could be deadly. An open loop system allows the water to thermosiphon continuously from the water tank through the stove and back again until a faucet is opened for use. For thermosiphoning to work without the need of a pump, the water storage tank needs to be two feet above the cold inlet of the stove for every foot of distance the tank sits from the wood stove. As the water continues to circulate through the system, it continues to get hotter. It is important to place the T&P valve (Temperature and Pressure valve) in the correct spot, so when the water reaches a maximum temperature or pressure, the valve will open and let the hot water escape to an area where it can drain safely without scalding anyone, thus preventing an explosion.
Our T&P valve will open once the water reaches 150 degrees. That is very hot water, and everyone in the household is aware of the potential temperature of the water when the wood stove is fired for days on end. After using this system for the past two years our water temperature has never exceeded 123 degrees F. We still have never had our T&P valve open. We have a 50 gallon hot water tank and with dishes, showers, and the weekly loads of laundry our water temperature never rises too high. If we were to maybe run the stove at full open for two days without using hot water, we may see the T&P valve open, okay, maybe 3 days.
Another reason water temperature needs to be regulated with a T&P valve is some plumbing can’t handle excessive heat, for example PEX piping. We plumbed our entire house with PEX; it’s easy, amazing, won’t be harmed if it freezes in the winter, but it can’t handle temperatures above 175 degrees very well. But that is okay, I wouldn’t want 175 degree shower. If I did, I would probably put coffee grounds in the shower head and brew a cup of coffee while scalding/washing in the morning. Seriously though, don’t try this.
I am very proud of the hot water system we use in the winter because of its efficiency. When the stove has sat cold for a few days, it usually takes an evening to warm up enough water for dishes and maybe a quick shower in the morning. During the cold season, we fire up the stove 24 – 7. We damper the stove down at night and in the morning open the stove and add more wood to the previous night’s embers. We went the entire month of January without having to strike a match in the morning to start a fire, the coals and embers would start up with a few bits of paper, a little kindling, and some dry wood from the wood shed. During this time of year, we have plenty of water for our domestic use without having to use our propane instant hot water heater.
We enjoy using the wood cook stove to heat our home, cook our food, and heat our water. We use the same wood to do all three tasks. I don’t enjoy cutting down trees, and I use mostly standing dead or fallen trees for firewood. Trees are a wonderful renewable resource that can be planted to replace ones which have fallen in the storms or died of disease. I have also been harvesting wood for firewood from our local dump when I can.
Other articles we have written and explore this system more in depth…
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