I am new to coal, love it even though it is a hassle to get in Rich. Va. Wood is for cavemen. I have a harman tlc 2000, want to make it control the air. I ordered a exhaust heat riser coil bimetal spring. Like old car choke spring but bigger. I am planning to have that affixed to the ash door connected with a light chain/cable to the air slider. A light extension spring would hold a constant pressure in the opposite direction , failsafe air limiting. I do realise the ashdoor is a cold slow response area for the spring, but too easy not to try, will experiment.