by matt walker » Thu Jan 17, 2013 11:15 pm
Hi Mike, what a cool set up! I have been hoping to get a system in my greenhouse but haven't done it yet, yours is pretty inspiring.
I think that you are on to something with your line of thinking, that the single piece sheeting doesn't allow much return air into the hoophouse, and therefore drags on the stove. As for where to put the make up air intake, I suppose you have some choices. If it's really cold where you are, I'd probably try to get it close to the stove so it wasn't pulling a cold draft through the length of the hoop house.
One other thing to consider is exhaust location, type, and whether there are significant pressure differences due to that. Do you have a vertical stack at the end of the system that reaches above the hoophouse? If not, that could be a large part of your problem. Not only does stack effect help at the end of the system, but if your exhaust is down low and straight out it could be experiencing pressure differences that are working against the system. If there is any breeze from the exhaust side of the hoophouse it will create high pressure there and low pressure on the opposite side, which often is enough to mess up the draft. If you can, stick a vertical section on the exhaust and get it above the roof line and see how that works for you. Give it a chance to get warm to the touch on the vertical run before you judge it's effectiveness.
For sure cover the feed when the stove is out, and the return air as well. Be careful covering the exhaust, if you still have hidden coals in the system you could fill the hoophouse with deadly CO. Probably better to see how well you can slow down heat loss by covering the feed before taking that risk.