Saturday, December 21, 2013

Backup Heating for the $2K Solar Space and Water Heating System

Our $2K solar space and water heating system provides solar water heating and also space heating to part of our house.  Until recently the backup heat for this part of the house was a propane forced air furnace that came with the house.  But, last winter the furnace died and the replacement cost was $6000.  So, instead of replacing the furnace, we added a backup heat system that just adds heat to the large solar heat storage tank when there is not enough sun to keep the solar tank warm.  This approach cost about $300 (pretty good saving), and has the advantage that we no longer have a noisy and potentially unsafe gas furnace hung from the floor just below our bed.

The new backup heat system is pretty simple.  Its just an electric hot water heater that sits next to the solar tank with a small pump to circulate hot water from the electric tank to the solar tank when the solar tank temperature drops below a setpoint.  The heat is distributed to the room above by the same radiant floor pex tube system as before.

The backup heat source electric hot water tank

The TopsFlo pump that circulates water between the backup tank
and the solar tank is at the bottom of the picture -- only 15 watts.

Diagram of the new backup heat system -- really simple.

I've added a new page that describes the backup system here...

And, updated a few pages for the project to reflect the new backup heat system...

There is also some discussion of other alternative backup heating systems -- I'd be interested in hearing any ideas on a better way to do it.


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