I have a small urban greenhouse that I'd like to heat. It's l8' x 12' (long width runs east-west), made of very heavy-duty aluminum, sits on a dwarf wall, and is peaked, and built against a tall masonry wall (on its north side). It has a single door in the west wall under the peak. There is no concrete base: the floor is clay/subsoil. We don't get serious cold here, on the south-east coast of England. Min temp mid-winter -5C (23F), av. winter 5-15C (40-60F). The heater is needed at night, but more particularly during the long weeks of gloom and cool temps that we usually get in July, just when the heat-loving fruit is gearing up to ripen. Loads of blight and mold in this cool moist clime (very like NW USA). Funny, I'm from NY State where I never felt the absolute need for a greenhouse, because we had reliable HEAT in the summer...
Anyway, I can erect a small shelter on the leeward side (NE corner), against the 9' masonry wall. Here's where the fire box could be, along with a box full of dry tinder. I'd like to make as big a firebox as is possible since I won't be sitting next to it to stoke it every twenty minutes. If I stoked it twice, running it for an hour in the evening, that would probably be enough for this tiny space. (?) The burn chamber could run into the greenhouse through the wall (recently built, and the guy who built it is still around, can cut the hole for me). The riser would be just inside the NE corner. I'm thinking ceramic pipe, say from http://www.schiedel.co.uk
, for the innermost flue of the riser? If it was ceramic would I still need to insulate it? As for the barrel, I'd like to try to avoid metal in that very damp environment. Maybe I could make it out of soft brick or fire brick? The pipe leading the warm exhaust gases away could be of clay sewer/drain pipe, available here with every possible join and and angle. The pipe could lead west through the center of the raised (2' high) bed on the north side, buried 2' deep or more in the soil. Before reaching the west wall it would make a left turn under the steps leading down from the doorway (currently just stacked bricks) into the raised bed along the south wall; then head back to the east wall of the greenhouse, through it and up to the roof. I'd need some sort of clean-out system, and maybe some form of insulation over the clay pipe, at least when it's running under the north bed, so it doesn't burn the tomatoes' and melons' toes, and also so there's some heat left for the south bed where the peppers and eggplants grow.
I've read the original Evans/Jackson book and have just ordered the third edition in case it can give me some new ideas. I'm considering the use of ceramic pipe for the burn chamber, but I guess fire brick would work as well. We have a small stack of it, left over from the masonry heater we had built inside the house four years ago.
Any thoughts? Is anyone aware of such a construction having been built anywhere near here, or the London area? No help from my English partner who thinks the whole project is a waste of time and money. Then again, she thought the same of the masonry heater, but the fact that we now use a single basket of wood per day to heat most of the converted sandstone barn we live in has gradually won her over. ; ) Thanks in advance for any suggestions.