I am in the process of building a small greenhouse (10 x 25 ) to keep some tomatoes and my wifes plants in this winter and am considering making a cinder capstone and tile firebox with a 1/2 cinderblock flue similar to the pottery patio fireplaces sold at Wal mart. I plan to line the fire box with ceramic tile, stack the blocks for the flue staggered to provide internal heat baffles that protude 1 to 2 in , alternating right and left, sealing the whole assembly with mortar. my thought is that this should provide sufficient heat with just a couple log ends a day being fed into the box . Has anyone else used wood heat for a greenhouse? What were your results?

-- Jay Blair (jayblair678@yahoo.com), August 18, 2000

Answers

Jay: I'm pondering similar questions. What I'd have to ask is are you trying just to keep it above freezing or warm? Especially if you're trying to keep it warm I suspect you're gonna use alot of wood if you live in the north country like us.

-- john leake (natlivent@pcpros.net), August 18, 2000.

In the past, I have pondered the possibility of wood heat in the greenhouse. I rejected the idea for various reasons.

1. Soot on the glass cutting the amount of light coming in. I HATE washing windows.

2. It's a dry heat that is not conducive to healthy seedlings.

3. Temperature fluctuations are too hard to control with wood heat.

Instead, I have used a small propane pilot light, a kerosene lamp or my favorite, a bin of hot horse and chicken manure to heat the greenhouse.

A good passive solar design for your region will go a long way in conserving fuel for heating your greenhouse. Tomato plants and most houseplants can tolerate temperatures down to 42 degrees at night without problems. More tender tropicals probably need to be kept no lower that 54 degrees.

I am sure there are others who can give you all the positive aspects of wood heat in the green house and I am interested in that side of it also.

Laura

-- Laura (gsend@hotmail.com), August 19, 2000.

Laura, explain how to use the manure to heat the greenhouse. I know how a hotbed works, is this the same idea and how large a greenhouse are you heating?

-- Cheryl Cox (bramblecottage@hotmail.com), August 20, 2000.

Hello, I use a woodstove to heat my 12x18 greenhouse. It works pretty good. I have no problems with soot. I would think having a nice tight structure would be the biggest concern for any heat supply. Mine's not so tight, so I can only raise the temp about 20 degrees, no matter how cold it is outside. I gain about 1 month on either side of summer, which is enough to enjoy far more cukes and tomatoes than I can grow outside here. I'm in the middle of Alaska and everything outside is already frozen, though I'll be able to eat out of the greenhouse for another month. Next year hubby wants to cover the whole garden! That we'll heat with a thermostatically controlled oil burner, like a Monitor or Toyostove. We want CORN! I have been told that an unvented propane heater has exhaust that is beneficial to plants. We burn mostly slab wood, which is free, but a hastle to get. My stove needs 'real' wood at night. Good Luck!

-- Jill Schreiber (schreiber@alaska.com), August 21, 2000.

In retrospect, I am thinking that the dry wood heat wood be a deterrent. What I may try to do is set up a radiant pipe heat system, using wood outside to warm the conductor. the other option , oil filled radiators (1 or 2)

-- Jay Blair (jayblair678@yahoo.com), August 24, 2000.

How about using the wood heat to 'hot up' some fluid (maybe a water/glyco mix) and then pass that through a heat sink of some kind. It would be a bit slow to start (depending on the size of the sink) but would continue to give off heat well after the fire goes out. How about a number of rock filled garbage cans placed around the greenhouse, connected with cpvc? Use a salvaged auto radiator (or whatever) as the heat collector. I'd expect to use a small pump to move the fluid around. Maybe do some earth berming around the outside if you're still in the construction/design phase.

How about adding seasonal insulation? Wall two or three sides with bales of hay. Would keep direct heat loss through wind exposure down and could be used as mulch next year.

I'm in N Al also and getting ready to build a greenhouse (of sorts) for the plants we brought with us from Fl. Should be an interesting season...

j a

-- j (jw_hsv@yahoo.com), August 27, 2000.