A simple Solar and Wood Water heating system

These diagrams will show you how to build a simple Solar and Wood Hot Water Heater that will preheat cold water on its way to your normal hot water tank. During normal use this setup will quietly supply some 40% to 80% of your everyday hot water needs. Your normal heater fuel will take up the remainder.

When you have extended power or gas outages this system will give you an independent and self-powered backup system. You will, of course, have to keep the water pressure up to make this system work. This setup assumes you already have a wood stove or alternative heating system with a flue that will be hot.

The Stove and Exchanger

The heat exchange jacket is fitted to the first few feet of the wood stove flue. It extracts the heat out of the escaping exhaust gases and puts them into the water. If the water tank is higher than this exchanger it will pump hot water to the tank by thermosyphon. The greater the height difference the better the thermosyphon. If a good passive thermosyphon cannot be obtained, you may need to install an electric circulating pump between the heater and the exchange jacket.

The Heat Exchange Jacket

The jacket itself is made of two lengths of stovepipe . One the diameter of the standard flue and the other the next size larger. Get some soft copper tubing of a diameter less than the space between the two pipes and bend it tightly around the smaller pipe. Drill inlet and outlet holes in the larger pipe and slip it over the assembly. Fill the space between with fireplace mortar or concrete. Anything to better conduct the heat into the copper pipe will improve the efficiency.

The Piping Diagram

The wood heater unit can be successfully combined with a passive solar batch heater such as the one diagrammed here to supply preheated water from either the sun or the wood stove.

This diagram should be considered to be general and schematic. Refine it with a skilled plumber.

from John Raabe: jraabe@whidbey.com

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