Fresh Air Duct (not combustion air) Tied Into Return Duct. Normal?

From a building science stand point it is problematic and of poor design. Especially in a residential setting.

I have been in residential HVAC for over 25 years and I have never seen a residential system with a fresh air intake tapped into the return duct. The only thing I can think of is they did it for combustion air, but you would not tap it into the return. Typically with an 80% efficient furnace, you would run combustion air if there is not enough air infiltration but in the attic, you should be fine. The insulation around the duct is not efficient either.

Welcome to our forum, Jesse!..Enjoy! :grinning_face_with_smiling_eyes:

I agree with Scott. It has been that way for 20 years or so here.

But I agree with the insulation.

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Just speaking regarding Michigan Mechanical code.

It’s not for combustion air, that’s an entirely area of the code.
The whole idea is to bring a certain amount of fresh in to meet air change per hour (ACR).
As I stated above, an ERV or HRV will suffice if the 4" intake is not used.
Flex duct is adequate with the idea of making sure it’s extended out to allow proper air flow, is with any flex duct installation.

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It’s not a problem, if you don’t mind your house smelling like hot asphalt in the middle of summer, lol.

I always put a damper inline after the AHJ left, in those areas.

Northern MI is not Detroit. :stuck_out_tongue_winking_eye:

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Yes indeed. As Larry indicated, a damper is necessary.

Ryan,
I don’t understand your comment on the asphalt. You were trying to be funny but it doesn’t make any sense.

I assumed asphalt shingles. Give em a sniff on a hot summer day. OP implied that furnace also has AC coil.