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Moving from exhaust-only to an HRV – outside venting question

hedirnbc | Posted in Mechanicals on

Hi all, appreciate any help you can give.

I live in Minnesota (6B on the climate map) and I have a 3 year old house with bath fan exhaust only. There are 3 bath fans on the second floor that run constantly. House is about 3800 sqft now and will be almost 5000 sqft when basement is finished.

I’m thinking about switching to a HRV while the basement drywall is still open and shutting down the bath fans. In mechanical room HVAC is high efficiency so plumbed intake and exhaust. There is a 6 inch flex fresh air in the mechanical room seemingly just for the water heater.

Can I grab the 6 inch fresh air for the intake to an HRV and then just run another exhaust? Or could I tee the fresh air to the HRV and leave part open to the mechanical room? Or will I need to run a separate intake and exhaust for the HRV and leave the open intake as-is?

Mechanical room is about 150 sqft and will be drywalled and have a door once basement is finished.


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  1. GBA Editor
    Martin Holladay | | #1

    If you have an atmospherically vented gas water heater -- and it sounds like you do -- then the 6-inch duct you describe is necessary. It provides combustion air for the water heater. You can't share that duct with the HRV, and you can't use it for any other purposes.

    Of course, if you decide to buy a new sealed-combustion water heater, or a heat pump water heater, the combustion air duct would become unnecessary.

    An HRV cannot provide combustion air. It needs its own dedicated ducts.

  2. hedirnbc | | #2

    Thanks Martin, yes that looks like the case. Happy I asked, thank you for the information.

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