Hydronic Stove Video Script
The main house heating system in the Seed Eco Home is the Hydronic Stove - a wood burning stove with a water pipe heat exchanger. The hot water is circulated in PEX pipes under the floor, providing comfortable heat - no cold feet.
The main parts of the heating system are the stove itself - the heat exchanger on the top part of the stove - the chimney for exhaust gases - and the PEX tubing under the floor. Here's how it works.
The stove generates heat. The heat exchanger - or more specifically - 16 sections of 1" black pipe - captures the heat and transfers that heat to water that is circulating through the pipes. The water then circulates the heat through the house. There are 4 coils of tubing, each 300 feet long, under the main floor. We are using 1/2" PEX. For the heat exchanger, we are using pipe elbows to make the connections. When you do that, use thread tape and pipe dope both - the pipe dope makes it much easier to screw the fittings on to avoid leaks. We did not use pipe dope. I had many leaks, which I sealed with JB Weld high temperature epoxy by pasting over the leaking joints. The joints are outside of the stove. The reason is ease of build - and access for serviceability. Because you don't know if you will have leaks until you actaally run the system at temperature. As the joints are outside the stove, they don't get hotter than the water temperature. To seal the air holes around the pipes, we welden on a collar and stuffed it with rock wool insulation. Rock wool, unlike fiberglass insulation, can take the heat of a stove. The heat exchanger has a total of 16 square feet of area, or an estimated 200,000 BTU.
The stove door is hinged and closes with a latch. A circular opening on the door allows either a blower - to get more heat - or a pellet burner attachment that shoots pellet heat into the stove. As such, this stove can run either on pellets or firewood. We plan on installing an open source pellet burner before winter ends. Underneath the door is an ash tray, which comes right out, with a handle on both ends for easy carrying.
The pumping and control of the system is done through the open source Hydronic Control Panel. To get the stove running for the first time, you fill the system with water and check for leaks. Then, fill the system with water. A fill valve is very useful - it allows you to reduce the pressure - typically 12 PSI for normal operation. This is important because it helps the system stay within the correct pressure. In our case, the overpressure relief would activate easily when we did not use the fill valve.
During intial startup, you have to prime the system. The fill valve appears to be indispensible for this. It allows you to fill the system at full pressure of the water system (44 PSI in our case) - by lifting the lever - thereby allowing you to purge the system of air much more easily. In our case, it was not possible for us to get all the air out until we added the fill valve. Once the system is full, we release the lever and the system pressure drops back down to 12 PSI once we let some water out.
Next is the Expansion Tank. Upon heating, water expands - about 1% (about 1/10000 per degree rise [1].
Future additions to the hydronic stove will include a pellet burner, as shown in the Seed Eco-Home Infographic. A pellet burner is more efficient - and it allows for automated operation. If you have a big hopper full of pellets - you may not need to load the stove several times per day - but instead - you go days or even weeks - depending on the size of your wood pellet hopper.