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Makeup air advice needed

Victoria Williams | Posted in Mechanicals on

I had a recent post asking advice regarding HRV vs exhaust only ventilation for my very tight energy efficient smaller home that I am building. Balanced HRV systems if installed properly could have exhaust lines in the bathroom and in the kitchen with boost capacities negating the need for additional exhaust lines.

The major stumbling blocks are the very high cost of proper installation and space requirement for the system itself for easy accessibility as well as space for the duct work.

So I am back to considering 2 pair of Lunos h2 fans which provide HRV capabilities and are more affordable, I would then install an intermittent exhaust fan in the bathroom (150cfm) with a timer switch and a modest range fan (220cfm) in the kitchen.

My question is: What can I do to supply makeup air to allow these intermittent exhaust fans to do their intended job? I will have a single heat pump in the main living area. My home will be 1ach50 or below. Thanks.

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Replies

  1. Charlie Sullivan | | #1

    Did you see that Lunos now has a model that can operate as an exhaust fan? The "eGO" it's called. It has dual fans that operate as an alternating pair, and then can switch to exhaust only. Much better for bathrooms and kitchen than the regular lunos as it won't spread smells and humidity like they do.

    There's also a Lunos knock-off available at Home Depot.

    As for your actual question, one consideration is whether you have any combustion appliances in the house, whether wood, pellets, gas oil, etc. If so, you want to make sure you don't depressurize and backdraft. If you don't, relying on leakage through the lunos and random cracks is likely fine. And leakage through the lunos allows some heat recovery.

    To add makeup air, you can have a manual vent you open, an electrically operated vent that is automatic when the fans turn on, or even an active supply fan. Since your fans are modestly powered, I don't think you need or want an active supply fan.

    If you are on the fence about what's needed, you could have the depressurization you get tested when have a blower door test done--just measure the depressurization with the exhaust fans on and the blower door off and covered.

  2. Victoria Williams | | #2

    Thanks Charlie. I did know about the eGo but it does not come cheap. The Lunos e2's will not be in the kitchen though there will be in communication with the kitchen as the floor plan is open concept kitchen/livingroom with a loft space over the 2 bedrooms and bath. The ceilings will be high up. I will not be using any combustion appliances in this house. Regarding the electrically operated vent.....where would it be located? And would it have a good backdraft damper?

  3. Brian P | | #3

    I don't know the optimal solution to your ventilation needs, but have a couple pieces of advice.

    You don't need that powerful of a bath fan, one of the 80cfm Panasonic fans would be more than enough if installed properly.

    If you are all electric and don't do a lot of heavy/greasy cooking, I'm pretty sure you would be fine with a recirculating range hood, no makeup air needed. Further, if you are a very light duty cook, you could consider no range hood at all (but at least wire for it in case you want to install later). Whether this is allowed by your local code and/or certifications is the question. This is what we decided to do in our house - no range hood, but we are wired for it if we change our minds.

  4. Victoria Williams | | #4

    Brian,
    Based on the demensions of my bathroom, the number of bends needed for the duct work and the length of ducts, I do need 150cfm. All the reading that I have done state that recirculating fans are suboptimal. Hense my desire for a modest range fan.

  5. Lucy Foxworth | | #5

    Victoria,
    If I understand the Lunos e2 HRV correctly, a pair of them provide their own makeup air because they switch directions every 70 seconds. We installed 2 pairs in my brother's house, they are very nice.

  6. GBA Editor
    Martin Holladay | | #6

    Victoria,
    For more information on sizing bath fans, I suggest that you see Bathroom Exhaust Fans.

    It's very rare for a bathroom exhaust fan to require a dedicated makeup air source. Almost all homes have enough leakage to allow bathroom exhaust fans to operate. If your house includes 4 Lunos fans, my guess is that these 4 Lunos openings will provide pathways for makeup air when the bathroom exhaust fan is operating.

    Range hood fans are another matter. If you don't want to install a recirculating fan, your range hood fan may need a dedicated source of makeup air, or you may need to discipline yourself to open a window every time you operate the range hood fan. For more information on range hood fans, see Makeup Air for Range Hoods.

  7. Victoria Williams | | #7

    Lucy, I would love to hear more regarding your brother's experience with the lunos fans!
    I will also check with their tech people regarding this question.

    Martin, Thank you as well. I actually had read your article a couple of times which promted my search for the Broan fans as opposed to recirculating models. I somehow missed the statemment "installing an outdoor air duct connected to a grille mounted on the kitchen wall" as a possible solution. I will check out Broan's website more thoroughly. Cracking the kitchen window open may also be a viable alternative.

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