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Makeup air system that won’t break the bank?

fgamache | Posted in General Questions on

I have a $700 problem and all I can find are $2,000 solutions….

New house build with wood stove & fireplace and 750CFM range hood == here in BC must have active (ie fan-driven) makeup air to compensate, proportionally, for the air exhausted.

The Fantech and Airscape solutions are ridiculously expensive….

Has anyone had any success in sourcing a reasonably-priced solution?

fg

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Replies

  1. Expert Member
    MALCOLM TAYLOR | | #1

    fg,

    Have you done the calculations to see how close y0u are to not requiring the make-up air? Off the top of my head I think it is a fan that exhausts more than half the interior air in one hour. If you are really close you might think of reducing the fan size slightly, which shouldn't have much of an impact on how well the unit worked.

    1. fgamache | | #4

      For my house volume, 0.5ACH is 260cfm... I am a long way away ;-)

  2. Expert Member
    Akos | | #2

    One option to go with an inline filter box and ducted fan. Simplest control would be to slave the fan to your range hood power switch.

    Something like a Fantech FB6 plus a 400 to 500 cfm fan (Power Vent-150x) would be under $500.

    1. fgamache | | #5

      I like that....
      Fantech's packaged makeup air systems have a nifty little controller with a CT doughnut that measures the current going to the range hood and when powered will a) open a damper b) power the makeup air fan proportionally to range hood and c) power an optional heater. They won't sell *just* the controller though, only as part of the $2,000 package.
      Achieving something similar (opening a damper, powering a variable speed duct fan) is what I'm looking for. Slaving the duct fan to the range hood is part of that solution but it's not the whole thing....

      1. Expert Member
        Akos | | #10

        Well, that can easy get that done with a small PLC and motor speed controller, adding the time and materials for that, I can gurantee you it will be way more then the Fentech, and most important nobody down the line will be able to fix/adjust it.

        The kind of in between semi DIY version is put say two or more current sensing relays (https://www.grainger.com/product/DAYTON-Current-Sensing-Relay-1EJF6) on your range hood's power. Have the output of each one feed to a fan dimmer switch which are combined to run the inline fan.

        Adjust the current sensing relay to trip at each speed set point of your hood and then adjust it's dimmer to get the correct airflow not to depressurize the house.

        Proper way of handling that much unconditioned air is another story, 750CFM of cold air is a big heater (40F rise is about a 10 kW heater). Might want to look at some of the commercial solution, I think they duct them near the range to avoid heating it.

        1. fgamache | | #13

          Thanks for the input -- clever dimmer solution ;-)

  3. rockies63 | | #3

    Why are you installing such a powerful range hood? You should read some of the articles on this site about sizing a range hood. You may need a hood that only needs to move about 150-250 cfm.

    https://www.greenbuildingadvisor.com/article/why-range-hoods-dont-work

    https://www.greenbuildingadvisor.com/article/makeup-air-for-range-hoods

    https://www.greenbuildingadvisor.com/article/dealing-with-a-high-capacity-range-hood

    As you are in BC what are you doing for whole house ventilation (HRV?) and for bath fans? How about make up air for the dryer?

    Don't forget about picking really good dampers for the ends of all those vent and intake pipes.

    1. fgamache | | #6

      Thanks Scott, I've read all those articles and agree -- most range hoods are shite.

      We both cook A LOT. Per your first linked article I searched for a LARGE hood (48" x 20") but thing is anything that size comes in high CFM. The 750CFM I got is nowhere near the top of the range... some of them are 1200, 1400 and up. You best hold on to a fixed part of the house when you turn them on lol. I *could* disconnect the 2 higher speeds of the blower and almost meet the 0.5 air exchanges threshold, but since I've got it, I'd rather use it if you know what I mean.

      As for your other questions, I'm not sure how that's relevant, but yes, an HRV is installed and will run 24/7 but that is balanced exhaust/intake so doesn't help with makeup air. No bathroom fans; but rather timer switches that will power the HRV on high for 20, 40 or 60 minutes. Dryer is low CFM and doesn't, per local code, require makeup air.

      1. Expert Member
        BILL WICHERS | | #7

        If the vent hood uses a capacitor-run motor for the fan, you can replace the capacitor with a smaller value (lower microfarad) capacitor which will result in all speeds being reduced (you’d still have 3 speeds, if it’s a 3 speed fan, but they’d all be slower). You’d need to be comfortable working with electrical devices to do this, you’d void any warranty the unit has, and you’d need to experiment a bit to find the right value “new” capacitor to get the speeds you want. Maybe this is an option for you.

        Bill

        1. Jon_R | | #11

          "If a wrong capacitance value is installed, it will cause an uneven magnetic field around the rotor. This causes the rotor to hesitate at the uneven spots, resulting in irregular rotation, especially under load. This hesitation can cause the motor to become noisy, increase energy consumption, cause performance to drop and the motor to overheat."

          https://en.wikipedia.org/wiki/Motor_capacitor#Run_capacitors

          1. Expert Member
            BILL WICHERS | | #12

            If you deviate too far from the “right” value, then yes, but otherwise it’s ok. Some switched speed motors actually control the speed levels this way.

            Bill

  4. Jon_R | | #8

    Depending on climate, you may need to add 60K btu to your Manual J design load.

    Perhaps it should be designed more like a laboratory fume hood.

  5. GBA Editor
    Martin Holladay | | #9

    F. Gamache,
    There's no free lunch. If you want a powerful exhaust fan that sends large volumes of indoor conditioned air to the great outdoors, you have to replace that exhaust air with an equal volume of outdoor air -- and that outdoor air needs to be conditioned.

    Makeup air units are expensive for a reason. That expense is a reminder that we don't really want a high-powered exhaust fan in the first place.

    Most designers of efficient homes settle on a range hood fan with a lower cfm rating than 750 cfm. That simplifies everything. But if you want a range hood fan that sounds like a jet engine, be prepared to pay for it.

  6. fgamache | | #14

    Alright.... Thanks for all the input.
    Seems the answer to my initial question is "no", there doesn't exist a reasonably-priced mua solution on the market.
    I am leaning towards disconnecting the top 2 speeds on the range hood fan, keep the lower two, and live with that rather than adding all the complexity.
    Cheers.

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