The collector is protected against freeze damage by the greenhouse itself, which collects and stores heat during the day. If the greenhouse keeps the plants in it above 40ºF, it will give the collector freeze protection – so long as the collector is correctly installed.

Insulate the storage tank

It is important to leave an air gap of at least 3” below the bottom fin and above the top fin in order to allow warm air from the greenhouse to circulate between the cold glazing and the collector at night. Do not insulate the back of the collector if there is any danger of freezing.

_{Figure 7}

In the winter the heat that the Big Fins loss to the house is welcome, during the summer it isn’t. If this is a problem you should block off the back of the fins with a cover of some sort. The only hazard is that you might forget to remove the cover in the fall and that the Big Fins, isolated from the house, might freeze on a cold night.