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Locating Bathroom / ERV Exhaust

Hawnes | Posted in General Questions on


I’m building a house that will hopefully be <1.0 ACH with R40 wall insulation. I’m in Vancouver, BC. Climate zone 4.

I’ve decided based on various factors so far to go with an ERV + Dehumidifier (how this will be ducted I do not know yet).

The purpose of the ERV is to help maintain the humidity at 45-50%. I have found in the winter in my leaky home currently with the heat on the humidity can be driven down into the RH 30% at 23C. During August for example humidity can shoot up to 60% at 23C – this is the purpose of the dehumidifier.

Now my main concern is whether the ERV should exhaust from the bathroom and laundry room. Or should I have bathroom fans separately and the ERV exhaust from somewhere else?

The reasons for this: the bathroom moisture I don’t want to come back into the home through the ERV; also, this will help keep the ERV core cleaner; and this would avoid having to “boost” the ERV cfm to the whole house just to clear out 1 bathroom for example.

(n.b. my home will have 2 floors, 4000sqft, 5 bathrooms)

My main setback would be the energy penalty for having the bathroom exhausts due to have a 6″ hole in the wall for it.

Any thoughts?

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  1. BirchwoodBill | | #1

    I am looking at the Aldes multi port exhaust fan that handle 4 baths with one opening. Each bath would have a backdraft register, and go into its own inlet on fan itself. There is one outlet from the fan that exhausts outside. For air balancing, Use a makeup air damper that opens when an exhaust only system is running, such as a bathroom fan exhaust, clothes dryer or kitchen fan. Not a perfectly balanced system but better than most.

    The exhaust penetration should be well sealed and the rigid metal duct should have mastic. The exhaust should be sloped so any condensate flows to the exterior. Some people use PVC pipe for the last 4 feet in the event you get condensate.

    1. Hawnes | | #4

      That's interesting. Thanks. Will look into it.

  2. AlexPoi | | #3

    In a tight house, I wouldn't use bathrooms fans because then you have to figure out a strategy to provide make up air. Otherwise, you risk depressuring the house or your fans won't be as effective as getting the air out. This is worst than overventilating the house for 20 minutes in my opinion. Plus, dehumidying in winter is often way more economical than ventilating.

    One solution, if you are concerned about boosting the entire system, are the Aldes ZRT-2 kits and CAR3 / Modulo regulators (don't know the difference between the 2). The CAR3 is a airflow regulator that will raise its static pressure to regulate the air flow when the air pressure increases. If you set it to 10 cfm, you'll always receive 10 cfm even though you boosted the entire system. The downside is it needs 0.2 in of pressure to work. It's still better than overventilating in my opinion.

    The ZRT-2 is a damper that is either fully open or otherwise acts as a regular CAR3 regulator. In normal mode, the air goes through the CAR3 and you can set it to a whatever flow you like like 10 cfm. When you hit the boost button because you need extra airflow to handle the moisture, it will open up the damper to circuvemt the CAR3 and boost the ERV speed. If you have CAR3 installed on all your other ducts, then the airflow will only be boosting in the room with the damper opened not the other ones. Of course, the system static pressure in the other branches will increase so your ERV will have to work a bit more to push the air out but it's better than overventilating.

    Check these videos and

    I don't know how things are in BC, but here in Quebec it's hard to buy these parts from a store. They only want to sell them to licensed contrators. Some US websites sell Mr Modulo online though.

    BTW, Venmar (and VanEE) now sells autobalancing HRV/ERV. This may help with your dehumidifier ducting problem. I'm planning to use that with some CAR3/ZRT-2 in my future house. Hopefully, they'll work nicely together.:-)

    1. Hawnes | | #5

      Thanks. The venmar unit looks good.
      Best of luck with your build.

  3. creativedestruction | | #2


    It would seem a missed opportunity to have an ERV system for balanced, energy-smart ventilation with the bathrooms omitted from it's design. That's not to say your concerns are unfounded, just my perception. Consider that a 4,000 SF house has a lot of volume to dilute the recovered moisture from morning showers. Sure, it will add to the dehumidification load but will it do so considerably more than standalone exhaust fans each with individual makeup air, and 10 extra holes in the enclosure with increased pressures from slightly-unbalanced ventilation?

    I'm no expert on ERVs but I wonder if there are any residential units with controls for enthalpy wheel speed or partial recovery bypass similar to what's described here:
    I realize that's at multifamily scale but they're describing the same problem. It sure would be nice...

    1. Hawnes | | #6

      Yea. Agreed. A bypass for the bathrooms would be great.

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