Plumbing the wood-fired/solar hot water system, part 2

Making good progress on plumbing our hybrid wood-fired / solar hot water system.

My first task was to install a thermostatic mixing valve on the hot water outflow to protect occupants from the very high temperatures that can develop in a solar or wood fired system.

Next it was time for a good ‘ol obsessive-compulsive marathon cutting and dry fitting all the copper. The pressure relief valve and the drain ports are re-purposed as the cold and hot outlets for the solar and woodfired loop, and are isolated from the copper piping with dielectric unions to prevent galvanic corrosion. These represent fixed points in space as do the hot and cold outlets on the stove pipe heat exchanger and the solar hot water panel. All these elements must be brought together with consistent upward slope so no air bubbles can develop and stop the flow of water, as well as with valves to isolate various parts of the system for maintenance. It took about 10 hours trying various configurations until I arrived at a functional and decent looking system. The next steps will be to build and place the solar panel so I can identify my final connection points and then I will carefully work my way through the system soldering all of the pipe together.

Unless I’m using a street fitting I always try to leave a couple of inches between fittings. Not only does this make it easier to solder but it also leaves room so if you make a mistake or want to change your configuration you can cut the pipe at that location and solder on a different fitting.

I highly recommend this dual three-quarter and half-inch Ridgid circular cutter. Faster, easier, and more accurate than any other tubing cutter I’ve used.

Ideally there are no valves between the heat source and the tank in a woodfired loop because an accidental shut off could potentially create a hot water fueled shrapnel bomb in the middle of your living room. With that in mind it’s really nice to have shut off valves so you can disconnect the system for maintenance or if a leak develops. I like to use these little T handle ball valves because they are much harder to accidentally shut off. I also wire them open for additional safety.

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