ASK THE EXPERTS: Solar Hot Water Collector Configuration

Intermediate

I’d like to mount my two 4-by-10-foot used solar water heating collectors in landscape orientation on my roof. While I’ve always assumed the larger pipes to be at the top and bottom on a collector, and the smaller tubes to run vertically, is there actually any reason that these collectors can’t be mounted with the smaller tubes running horizontally? Assuming that they’re plumbed in opposite corners, and I’m using a pump, does it matter if I’m collecting heat while the water is moving vertically or horizontally? Or do I need to get collectors designed with headers along the long axis and short risers for landscape mounting?

James Root • Redmond, Oregon

If this is an antifreeze system, the collectors will work fine in the landscape orientation. They will also efficiently produce hot water in a drainback system, but can cause future problems. After years of use, the smaller riser tubes may not have the structural integrity to withstand the force of gravity. Most of the small tubes sag over time; this can create a “trap” that holds water and can cause freeze breaks in the tubing in the winter. Some manufacturers specifically exclude landscape drainback systems from their factory warranty due to the “tube sag” possibility. If you mount the collectors at a more radical tilt angle, like 20° to 30° from the horizontal, it will probably be enough to offset any future tube sag.

If you live in an area that requires adherence to Solar Rating and Certification Corporation standard 300 to be eligible for state, local, or utility incentives, your mounting strategy might be problematic. In this case, the manufacturers’ instructions must be followed closely, including mounting orientations. However, this probably won’t be the case with your used collectors since most, if not all, incentive programs require new equipment for incentive eligibility.

Chuck Marken • Home Power solar thermal editor

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