A Large Solar Space and Water Heating System in Iowa

This is a very nicely done system by Thom that provides both solar domestic water heating and solar space heating.

The 200 sqft, homemade collector with twinwall glazing.

This is a drain back system with the 300 gallon heat storage and drain back tank located about 50 ft from the collectors in the house.  When the sun is off the collector and the circulation pump is not running, the water in the collector drains back to the tank in the house for freeze protection.

The collectors are modeled after the $1K Solar Water Heater design in which aluminum fins are thermally bonded to copper pipes.  This design provides 96% of the performance of commercial collectors at 1/5th the price.

Thom bonding collector fins to copper tubes.

The lines between the collector and the heat storage tank are run in a trench through the yard.  As the picture shows, the pipes are packaged up in XPS styrofoam insulation to reduce heat loss.

Insulated pipes going into the heat transfer trench.

The tank is an EPDM lined and well insulated plywood box.   It holds about 300 gallons.  While this kind of design may initially give you some pause, it is a well proven design that goes back to the 1980's and has a very good track record. 

Thom is using the system for both domestic water preheating and for space heating.  The domestic water preheat is accomplished by running the cold water supply through a 300 ft coil of PEX pipe that is immersed in the tank.  This is a very effective preheat system that is 100% efficient for most water demands, as the water in the pipe gets preheated to full tank temperature.  A 2nd copper pipe coil heat exchanger supplies water for space heating to a radiant floor.  Depending on the details of the plumbing, it may not be necessary to use the copper pipe coil -- some have just pumped hot water directly from the tank, through the radiant floor and them back to the tank.

The EPDM lined tank with the two heat exchanger coils.

 All in all, quite a nice system :)
Thanks to Thom for documenting it so well.


I feel a bit of a part of this system myself, as Thom and I exchanged a record number of emails during the project.  Its really nice to see it up and running :)

Thom experienced some start-up difficulties with the system, and I have to admire the way he handled working through these -- things don't always go smoothly, and after putting quite a bit of effort into building a system, it takes some real discipline to work your way through unexpected start-up problems.  Thom has done a good job of documenting these.

All the details on the system on Thom's website...

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Gary