We’re far enough out of town that natural gas isn’t an option for fuel, so our home uses propane. We had reduced our household propane use to about 200 gallons a year. Then we started making cheese, heating the water with two propane-fueled tankless hot water heaters. It takes about 20-30 gallons of propane to pasteurize a batch of milk (depending on the size of the batch). Last year we went through over 600 gallons of propane, and this year was likely to be more. So we’ve been looking for alternatives.
Wood is the obvious choice. It is readily available, can be sustainably harvested, has almost zero carbon footprint, and best of all is very inexpensive. In a sparsely-populated area like ours, the particulates don’t present a problem. And obtaining it counts as an exercise program! But wood-fired boilers online have price tags starting at $3,000 – way out of our budget this year.
We’ve been talking to a friend who welds about building us one. He was interested because, if it worked, he wants to build one for his own use. After much research and contemplation, we settled on a dual tank design where the inner tank serves as a fire box and the outer tank surrounds the firebox with water. A trip to the local recycling yard netted us an old air compressor tank and a 100-gallon butane tank. Then my friend went to work. He added a door to the firebox, and a piece of scrap 6″ pipe to carry the smoke out of the firebox to the chimney; this runs through the water tank, allowing the water to absorb extra heat. He added attachment nipples and a pressure relief valve.
As for the all-important cost, the two tanks cost $75 at the recycling yard. Parts and labor cost another $350. Plumbing materials cost about another $350, for a total cost of about $775, which is less than the current cost of a tank full of propane. Wa-hoo!
When my friend had finished, he filled the boiler with water and started a fire. In 40 minutes, about 70 gallons of water had been heated to boiling! I took it home and hooked it up, adding about 60 feet of plumbing to my already-tortured vat heating system. Bur my results were the same: 40 minutes to boiling, and 185-degree water at the vat. With the tankless heaters, because of our high altitude, we have trouble maintaining 160 degrees at the vat. Not only will the wood-fired boiler save us money and reduce our carbon footprint, it will help us heat the milk faster, too!
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