I'd be interested in your findings since I have been looking at a few units but can't find room in the budget for one. I have used a Harmon coal stoker until a few weeks ago and replaced it with a wood burner for two main reasons: 1. the 85T BTU just isn't enough for a 20x96' GH; 2. The coal kept getting wet in the hopper and bridging up from GH humidity. You might want to look into the second problem possibility for a corn burner if it will be a stoker type.

I should add that I have another identical Harmon Magnum coal stoker heating our house with no similar problems. I have much praise for this stove for its intended use. However, the GH environment creates strange new problems.

You don't need to put woodburners or alternative fuel burners in the g'house environment. I'd very seriously consider a freestanding housing with a burner with a boiler to produce hot water heat for g'houses, if you have a woodlot or access to one.

Know a fellow who just did that. His set-up is a real honey. You can find these kinds of units in many farming magazines.

I'd agree with advantages of the outdoor freestanding unit idea Calliope, but therein is where heating gets pretty pricey. I was really impressed with an outdoor furnace demonstrated at Penn State's Ag Progress Days last summer that could burn any grain. they were burning soy hulls for the demonstration. the price for the unit was even tolerable. but after I started asking prices to get heat into a greenhouse my opinions quickly changed.

In order to get hot water from the outdoor furnace to any structure you need 1. A pump, 2. a heavily insulated water line, preferably underground, and 3. a heat exchanger unit inside. Furthermore, the circulation fluid can't be allowed to freeze when the unit isn't in use in the middle of winter. Most maunfacturers recommend a concrete pad to set the furnace on and unless you want to carry the fuel long distances you also need a storage shed nearby.

Instead of $15-$200 for an inside wood or coal stove the outdoor units are selling for >$3000. I think Soycandle is looking to save money with the fuel prices as high as they are. Possibly a home rigged setup/teardown unit could be built for less. I read about one case where a car radiator with an adjacent fan was used as a heat exchanger in a greenhouse. I'm going for simplicity for greenhouse heat strategies in the future. Hopefully the worst of the cold nights are behind us now and most nights won't require supplemental heat.