Monday, February 21, 2011

A $2K Solar Space and Water Heating System

We have been working on a very simple solar system that will do space heating and domestic water heating from the same system.  Its a very simple system that takes only regular DIY skills to build.  Nearly all the materials can be picked up at the local Home Depot type store, and the ones that can't have good online sources.

The collector for the new system

I've documented this system better than any other system on Build-It-Solar -- there are over a hundred pages of design and build information that should make it fairly easy to adapt the system to your situation.  There is also a lot of material on how stuff works and on other alternatives for each part of the system -- a bit of a text book on solar space and water heating.

Collector before painting.

We used twinwall polycarbonate glazing.

The system design is based on the $1K Solar Water Heating System that many people have built with good success.  It uses the same drain back collector system, and the same single large, vented to the atmosphere drain back tank.  It also uses the large coil of PEX heat exchanger for domestic water preheat.  The differences are that the collector is larger to provide extra capacity for space heating, the storage is larger, and there is a new system to distribute heat from the tank to a simple radiant floor loop.

The new radiant floor system just takes water from the top of the tank, pumps it through the floor loop, and returns it to the bottom of the tank -- no heat exchangers, no antifreeze -- just a little PEX tubing and a pump.

The new pump for the radiant floor loop.

We used a staple-up floor loop with insulation under.

This is the big coil of PEX that serves as the domestic water preheat heat exchanger.

The system is about as simple as you can get for a full four season, cold climate solar space and water heating system.  Simple is good (I think)  -- for airplanes or solar systems :)

It could (and should) be expanded with more collector area and more tank size to be able to do more space heating.  We would have added more collector area if we had the space for it on our south wall.  We do already have a dedicated solar space heating system, so this new one gets a part of the house not heated by the existing one.

The total cost of materials was a bit over $2000.  The system could be built for as much as $700 less, but we opted for "higher end" choices in the glazing, trim, and controller areas. 
I would estimate that the price for an equivalent commercially installed system would be north of $15,000  -- so the cost saving is significant.  Based on the 3 year payback for the $1K water heating system, I expect the payback for this system to be 3 to 4 years.

I'd very much like to hear any comments on how the writeup could be improved, or on things that are missing or not clear -- you can add a comment here or email me at

All the details on the new space + water heating system...

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