Got a princess same problem until I checked draft with Manometer and then added 2 key dampers.
Doc, with 30ft combined (double black pipe and stainless double/triple) you got a freight train worth of pull on the stove. I bet your at .2 when the flue is hot, or more.
Here is what happens, The air in the flue collar makes a hard 90 degree turn and straight toward the cat then up around to the air wash. Think of snaking a rope from the chimney, though the stove collar through the cat around to the air wash to the T stat. The more draft vacuum you have the tighter the rope gets pulled and what happens is the T stat doesn’t get hit with as much hot air.....because the air is following the straightest path though the stove, so the t stat opens more, more heat goes up the flue, the flue pulls harder. It’s just inefficient as hell and a lot of the hot air in the box gets dumped out the chimney. Plus the higher volume of air going though the cat is inefficient to as the cat works best with a lower volume of air going though it. The overall heat output to the room is is similar to a correct draft situation but there is a huge amount of wasted hot hot hot air going up the chimney. My guess is this is also the problem associated with short cat life as well.
The biggest give away I saw was when the dampers are almost closed and the stove is at .04” instead of .2, the thermostat actually gets satisfied and darn near closes even on high.
Try it. Run the stove over drafted on high for 30 mins and close the t stat quickly and listen for the clink (which is the t stat going to the zero position and deadheading against the metal stop), note where that happened in relation to the dial. You. For instance might here the clink at the 2:45 position with excess over draft and if the draft is right you will hear it at the 4:00-4:30 position.
This is the reason the t stat is not well equipped to deal with overdraft efficiently. I couldn’t believe how much less wood the stove burned fpr the same heat when the draft is proper.
Keep in mind when you go from high to low the draft goes way up because the t stat closing puts the brakes on the chimney by drastically reducing flow and the vacuum goes way up, creating more of a problem until the stack cools.
Get a manometer, and stick it in the hole where the ca gauge is and it will show you how much draft/chimney vacuum you have.
This is the cheapest I’ve seen and what I use.
https://www.globaltestsupply.com/pr...MIl6qnoNvd3wIVg0ZeCh0jSwHgEAQYBCABEgKmZfD_BwE
Get a little 1/4” copper pipe at menards and stick the hose end into the copper pipe with some silicone to seal the hose to the copper pipe. Then stick the copper pipe end into the cat thermometer hole. If you don’t see the copper pipe the rubber hose will melt in 1 sec.
Hope that helps.
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