I don't understand how you guys are getting by without boiling over in the summer. I was very meticulous at sealing the firebox and ash door with silicone and still had to bleed some heat off with a pair of 100 cfm fans across a heat exchanger in the shop. The first idea I had was to trigger the main hx fan with a temp controller, but the garage gets HOT, and very quickly when closed up. If left on I'd say the heat would build up to 140+ on a hot day? - just an educated guess.
So with the two small fans there is enough bleedoff to prevent overshoot under normal conditions with any type of wood. I'm content with the design, the shop doesn't get over 110 like this. Tonight the shortcomings were apparent. After a reload I checked the ash drawer and closed it back up. The lip that seats in the drawer seal wasn't seated completely, offset just a little. This created a considerable air leak. About 30 minutes later the over temp alarm sounds - fortunately I'm at home. Flue temps were 450 (they're usually 150-250 during idle).
I'm just brainstorming here, hopefully someone might throw in a slick idea I'm not thinking of. Perhaps there is a simple answer for a second stage of heat bleedoff. A small, 10 plate water/water exchanger crossed my mind, but then pumps, and a tank would be required. A small heat exchanger in the window is an idea I guess, but it has a pile of implications as well. How about an electric valve that opens and dumps some water outside after passing through the main DHW hx? Don't those get stuck?
I'm just a rookie boiler operator, not sure what everyone else does, but would like some more aggressive way to pull heat out that is automated.