hsvhel:

 

Disclaimer, have not fully read the last 3 pages....

 

When we reno'd in 2019, i went overkill on the CFM for the kitchen, as a result, if the extractor is operating, even low,  the fireplace can flow chimney exhaust into the house via the firebox normal intake.

 

slight overlook on our part

 

 

 

Similar situation for me, in that my rangehood has a peak flow rate of 1600m³/hr I think.  Given this and as the house is relatively airtight, when the fireplace is going and even with the rangehood on low, it can compete with the fireplace and pull smoke from it.  Given this, I just open a window somewhere in the house and that seems to alleviate things, though does mean pulling some cold air in for a time, which isn't really a bad thing given the fireplace can get going.

I do find this air movement handy in summer, as during crepuscular hours when things have cooled a little outside, I run the rangehood for a period (default timer of 15 mins usually and without the filters on), and it pulls a fair bit of cool air into the house having opened windows around the place.

Yann