back puffing

We have a Dutchwest Federal Airtight that is 20 years old. It has a catalytic combustor. We have a triple wall 6" pipe that goes through the second floor. We like the woodstove a lot but the problem with back puffing seems to be increasing. I think back puffing is the right term. Smoke occasionally comes out of the air intake (damper) on the side of the stove when we have the air directed through the cat. It can be quiet little wisps or a lot with puffing sounds. We have cleaned the stove pipe, replaced the combustor, replaced the gasket on the side door and checked the other gaskets. I read that one should let the temperature at the combustor get to 500 before shifting the air through the combustor so we do that. The puffing can be stopped by bypassing the combustor, closing the side damper and opening the lower damper wide open. (This is no fun in the middle of the night.) Our current solution is to open the side damper a little way and supply air through the bottom. Is there something else we should check? Or a different way to operate the stove so this is not a problem.

Is your chimney centrally located in your home or on an outside wall?

The latter can create backdrafting since a cooler chimney here facilitates retrograde cold air.

If it's this, sorry, the solution is tough but not as tough as putting up with smoke in your home.

Aye,
Marty

The chimney is inside the house but near an outside wall.