My 10 x 12 HFGH is in a warm climate where we have rare nights when the temps plunge to the teens. Last night was predicted a low of 20 degrees.

My 'heat sink' is a series of four 50 gal. barrels connected with tubing. The water is circulated at intervals by a small pump. The effect is that on moderate days, the temperature stays more even.

When the sun goes down, heat is quickly lost from the GH when outdoor temperatures are near freezing or lower. Late yesterday afternoon, it was 44 outside and 64 inside as the sun went down. I adjusted the thermostat on the little electric heater to just come on at 64 or lower. We rigged a 250 watt infrared bulb on the opposite side, not pointing to any plants.

At 4 am, the temp outside was 24 and the GH was at 34.

When I checked the plants at noon today, the only obvious unhappy camper was one strobilanthes that was wilty, despite having moist soil. I have no overly tender expensive topicals to worry about, mostly rooted cuttings, and plants that would probably be killed to the ground but survive outside in the ground, like gingers.

My point is to give some idea of the limits of 200 gallons of water, a 250 watt heat lamp and one little electric heater on a near 20 degree night for those who have asked about heat lamps, water and electric heaters. By mid-morning, in the sunshine, I had to vent the house a bit.

We have also tried a Coleman camping heater -- pricey for gasoline. We have a kerosene heater in case the power fails, but we've not used that yet.

I hope this answers some questions that are frequently raised here about the effiency of some methods. I suggest what Orchiddude (among others) recommends for heating in all but the warmest zones, and bottom heat for starting seeds midwinter.

Nell