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Space Heating For Free, Forever

by Doug Pushard

Most projects I design are fairly standard rainwater or thermal solar systems, but every now and then I get to design one that is far from routine. One such project involved space heating a small master bathroom for a local couple who cares a great deal about living a small energy footprint.

A small electric heater would suffice for most folks. But this couple, who get monthly checks from PNM, weren’t about to have an electric heater diminish those checks and the joy they receive in cashing them. The master bathroom occupies the northern-most room in the house and in the winter the temps hover around a chilly 58 degrees. It is adjacent to the master bedroom so noise was a concern.

From the beginning the design hovered around how to retain and radiate heat out at night. The problem with this solution, however, was that most tanks are not attractive and there was no place to put them out of sight. Building a small addition outside was a possibility, but overkill.

Fortunately, the owner recalled seeing an apparatus years ago — passive thermal storage tubes — that are used to collect and radiate warmth passively in rooms with southern exposures. They are reasonably attractive and lightweight.

The manufacturer had never installed these tubes in an active solar system, but assured us they could handle temperatures up to 180 degrees, which was more than we needed. From here all that was needed was to find a low-energy, low-noise pump that could handle the lift from the bathroom to the roof. Add a single 4x10 solar thermal panel and we were ready to install.

It was getting to be late fall and the nights had already dropped into the low 30s, so installation was timely. Temperature of the panel starting reaching 120 degrees late in the afternoons and the bathroom heating to a comfortable 72 degrees in the day with about a 4 degrees drop overnight. As long as the sun shines the room warms up, and when it’s cloudy, the room retains its heat for a few days.

The resulting system heats not only the north bathroom but releases heat into the adjoining master bedroom. It is quiet and should supply decades of heat with very little maintenance. Best of all, they get to keep getting their monthly checks from the power company. Bring on the sun.





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