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Central Fan vs. HRV

hedirnbc | Posted in Mechanicals on

Hi all another question.

Background: 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. We have been running the furnace fan constantly recently to keep the house even in comfort, I’m experimenting with “circulate” vs. always-on. Furnace is high efficiency but with an old school motor, not ECM. I don’t see us proactively changing the furnace in the near term.

I’m thinking about putting in a central fan ventilation system or a HRV before I finish the basement. I’m biasing towards the central fan, motorized fresh air duct approach since my current thermostat can run that system as-is. This will minimize cost and complexity, less new holes to put in the house. Since we run the current fan anyway the costs of the fan running won’t be incremental. Once I do either option I’d like to have the bath fans either run less frequently or only when needed (shower, etc.) in the bathroom.

Any thoughts on my decision(s) here?

Thanks,
-Ben

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Ben,
    Furnace fans motors that aren't ECM draw between 400 and 800 watts, with 500 watts being typical.

    If you operate your furnace fan continuously, how much does it cost per month?

    24 hours x 30 days = 720 hours per month
    500 watts x 720 hours = 360,000 watt hours/month = 360 kWh/month

    At 15 cents per kWh, that costs $54/month, or $648/year.

    In other words, running your furnace fan continuously is expensive -- especially if you don't have an ECM blower.

    If you purchase a FanCycler control, that will reduce the number of hours that you operate your furnace fan -- unless, of course, you perversely insist on keeping the furnace fan operating for 24 hours per day.

  2. hedirnbc | | #2

    Martin, good point. I see an option for an Evergreen ECM retrofit as well that I might take to reduce costs.

    Assuming I get the ECM in place i'm thinking about using a motorized damper to introduce fresh air versus getting an HRV. Any further thoughts on that piece?

    Thanks,
    -Ben

  3. GBA Editor
    Martin Holladay | | #3

    Ben,
    A central-fan-integrated supply ventilation system costs less to install, but more to operate, than an HRV.

    It's up to you determine whether the advantages of an HRV are enough to justify the appliance's higher cost. For more information on this issue, see Designing a Good Ventilation System.

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