Problem with smoke

[triptester]

My son has a older home with a fireplace and gas boiler . The chimney is masonry with twin flues. Since updating windows and cutting down on drafts a problem has developed where smoke from the fireplace is being drawn back down the the gas boiler flue. Does anyone have a solution for this problem?

 

[Nofossil]

My son has a older home with a fireplace and gas boiler . The chimney is masonry with twin flues. Since updating windows and cutting down on drafts a problem has developed where smoke from the fireplace is being drawn back down the the gas boiler flue. Does anyone have a solution for this problem?

I expect that providing an external air inlet to the fireplace would solve it. He's drawing a vacuum in the house, and the only way that air can get in is down the other flue.

My fireplace is set up with inlet ports on either side that are ducted to the outside. May be hard to accomplish as a retrofit.

 

[elkimmeg]

Does he have a chimney cap covering both flues? If he does the roof of that cap creates a channel for the smoke to return down the burner flue
If he has a single cap covering both flues then it should be removed the next step is to increase the exit distance between the flues, meaning to raise the fire place flue 9" above the burner flue

 

[triptester]

The chimney has 3 separate flues about 18" apart. The north flue is cemented shut. The center flue is for the fireplace with its own cap .The south flue is for the gas boiler with separate cap.

 

[webbie]

See:
(broken link removed)

We also have nicer looking ones, like the enclosed. Separation of the exhaust heights usually solves this problem.

 

[triptester]

My fireplace flue is several inches shorter than the gas flue. Which one should be higher?

The third flue that is cap shut ,could it been intended for a fresh air intake feeding up from under the fireplace?