Stressbaby, my two exhaust fans exchange all the inside greenhouse air every one minute. The problem with relying on air exchange is the additional 8 - 10F over outside temperature means that on a summer 95F degree day, the greenhouse temperature is 105F. This is much to hot for growing plants. Ned, our humidity during the summer is around 25 percent, so evaporative cooling pads work well to maintain the greenhouse at proper growing temperatures. In fact it is the place to be in mid July.

Thanks for all the replies We had our first rooftop frost this morning when it got down to 38 degrees. Tonight is supposed to be mid-30s with no wind ... so they're predicting a heavy ground frost. So I guess I'll be putting everything up in the greenhouse for the winter this everning when I get home fom work. At 38 degrees outside, my greenhouse was 42 degrees inside this morning with just the four 55 gallon black barrels full of water. I think I'm going to go with a 24K Modine "Hot Dawg" vented heater.

rottford-

hows the heating of the greenhouse going? what temperature r u heating it to and how much is it costing you.

next winter i will be moving my indoor citrus and tropicals to my garage which is about the same size as your greenhouse. wondering how much its gonna cost me to heat

I've got my thermometer set with a 6 degree gap. I have it set to come on at 62 F ... and it cuts off at 68 F. It keeps the heater from "short cycling" and building up condensate inside the heat exchanger. It's costing me approx. $200 per month. We've had some really cold nights below 15 F .... so it's been running ALOT. I can't complain though .... I've already got lemons, oranges, limes, and manderins set on my trees during the last 3 weeks I'm also rooting grapevines for a friend, and have started cabbage, pepper, and tomoatoe plants for my spring garden. I think when this single layer of vinyl needs replacing, I'll spend alittle extra money and cover it in 6mm polycarbonate. It should make it more efficient and save me on propane ... which is now over $3.00/gallon here

wow- $200 a month is alot for a small greenhouse- my garage is made of brick and is about the same size as yours. most nights its around 30-40 but it does occasionally get down into the teens. I wonder how much it would cost to heat the garage- i guess it will definitly pay to insulate the garage

The 6 mil polyvinyl I use is probably the least efficient covering (and cheapest) you can use. A brick/mortor garage that's insulated probably would not cost more than $50/month to heat with a small unit heater.

Rottford, I just purchased 1000 gallons of propane last week, the price here in Colorado was $2.19 per gallon. The sides and the south end of my greenhouse are covered with twin wall polycarbonate, the roof is covered with double air inflated 6 mil polyethylene film. Double layered polyfilm that is air inflated in between the two layers, keeping them 2-3 inches apart, is much more efficient, heat wise, than polycarbonate, and a lot less expensive per square foot. If you purchase greenhouse grade polyethylene film which is Teflon coated to prevent degradation by the sun, the film has a normal life span of 5-6 years. - Millet