Wood burning fireplace on 13 year old home in Wisconsin. Exterior wall with cantilevered chase. During blower door test I found noticeable air leakage to the inside from above the metal firebox. Would naturally suspect air leakage from the top and back of the chase. However, there are 2 air intakes on the chase - one is for outside air to the firebox as expected. The other one seems to be just an open vent to the chase. Outside air was freely entering the 2nd vent and into the home while building was depressurized.

Anyone know what this vent is for, and does it need to be there?

I don't have a picture, but the two exterior vents were side by side. Sorry too that I don't know the make of the fireplace. They have no complaints with the fireplace area, but I'd like to know.

 

Thanks,

John

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I imagine is pretty hard to tell much without the brand and its installation instructions to know what was required for that particulare fireplace model; not all fireplaces are built nor installed the same. It'll be interested to know how well sealed and insulated were the cantilever and chase before installing the firebox.

Does this home has a second direct vent fireplace between the 2 side windows? 

That is correct Armando.

I'm sure we won't be doing anything intrusive with regard to the chase, but I'd like to know if we could seal off the vent, as that was certainly a pathway for outside air to enter into the home.

Yes. Its correct.

John:  The chase is unlikely to have been treated as "conditioned" space by the builder.  If it is not air sealed it performs basically like a small garage with a fireplace instead of a car in it. 

Current code requires an air barrier in the fireplace chase, but I have never succeeded in retrofitting a chase like the one shown in your picture.

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