Are you saying the fireplace allows smoke into the house when you burn a fire? Do you have a tile or metal flue pipe?

Is one of your fireplaces in the basement? I have this problem. If I light a fire in the living room, it gets sucked down the other flue to the basement fireplace and smokes up the house. I'm told the chimney is too short for the house. Maybe an extender would help.

You could put in inserts. They are better for heat anyway.

You're starting your fire too large too fast. Cold air is dropping down the flue, pushing the smoke out. Start small, heat it up slowly, and reverse the problem.

It's a masonry fireplace and I've tried everything I read online but still have smoke coming in

I'm preheated chimney by holding burning newspapers up in

@Audrey Drake, how are they "twin" fireplaces? What are the temperature extremes where you live?

We're about an hour north of Minneapolis, so winter temps can be 20 below for a week or two at a time. (30 below is rare, but possible!)

Our fireplaces - one on the main floor, one in the lower level are located on an inside wall, essentially on top of each other. Each has its own flue, side by side, & a we have a Chimilator Deluxe on each of the caps. These seal very well, and I think keep the chimney from needing to be "pre-heated".

When not in use, the Chimilator cap is sealed, as well as the damper completely closed.

We also added this to the fireplace in the lower level, since it has the much longer flue:

26" High Efficiency Log Grate

(There is also a 21" size.)

Our house is 3 story, so both flues are long.

We've never had a problem getting the fire to light or stay lit, although I don't think I would ever try to have both of them running at the same time.