I have a 23D x 26.5W x21.5H fireplace insert that I'm modifying for my greenhouse. I'm going to add secondary burn tubes and water circulating tubes for hot water. I'm going to line all sides with fire brick leaving the top uncovered to allow heat to soak into mass on top. My questions are (1) should the baffle in the top be flat or slanted (2) should the opening to the stack be in the front or back (3) should the water line be above or below the baffle (4) is there a minimum/maximum opening for the baffle to the stack?
These are a couple of resources that i like to share. Diy level.
The best efficiency gains i have personally seen are had using the smoke shelf ( "baffle"?) And a combustion air intake from outdoors.
Our smoke shelf burned through and radiation plummeted, but gradually. I re built the shelf and it radiated an amazing difference into our living space, an immediate and undeniable improvement.
Same for the addition of the outdoor air intake. It is hard to relay the improvement. We used to cut all firewood from dead timber, with a bow saw and haul 1/2 mile home on a train of snow sleds.... on foot. The work required to keep comfortable temps was so reduced, that i will not operate without this key feature ever again, plus it consumes less precious resource.
Frank Li thanks for your reply. The articles were helpful but the fresh air tip was something I hadn't thought of. This stove is heavy steel about 450 lbs without firebricks. The whole top is flat so I intend to stack stone on top. Should be able to pick up granite pieces at a counter top supplier. I've been using brick pavers on my current stove but it loads from the top and is a pain to set up each time. The position of the smoke shelf is the first thing I'm going to work on in my new stove. The original shelf only covers less than half of the top and is at a pretty steep angle. I intend on making it larger and decreasing the angle unless that will cause problems. Any thoughts on that?
I don't know if the countertop place has soapstone, but if it does, you might want to get it instead--or in addition to--granite. We have slabs of both. The granite is on the stove top surface, and the soapstone stacked on top of the granite. After the fire dies down, the granite cools down way before the soapstone, even though it was initially hotter than the soapstone as it was in direct contact with the stove. The soapstone really retains heat for a long time compared to the granite!