GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Duct sizing for ERV

lesley_ | Posted in Mechanicals on


We are about to install a Broan 180 AI ERV in our home. I have spent a lot of time researching and thinking about how to go about this. This is my most recent duct layout and I was hoping to run it past people who know more than I do. My main questions-
1. Is an 8″ trunk line for supply and return a good choice?
2. I am planning on reducing the blue supply line down to 7″ and then 6″ for the branches with 6″ flex pipe to the registers. The return line (red) is 8″ trunk and 6″ branches, mostly flex pipe.
3. Do I have to make the outside supply and return 8″ instead of 6″ if the main trunk is 8″?
4. Anything look drastically wrong or could be improved?

I have attached my layout for reference. The ERV is located in the laundry room and will be ducted up to attic. The ducts will be rigid ducting wrapped with insulation and under blown in. Zone 6. Thanks!

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. eust2023 | | #1

    I just installed a 130 cfm Broan and only ended up with about 110 cfm due to the duct loses. The minimum exhaust require for a bathroom is 50 cfm. I would only exhaust from the two bathrooms giving you about 75 cfm each. I think that you are oversized on the supply ducts but not my expertise.

    1. lesley_ | | #2

      Thank you! I still have good bath fans, so those would be used during showers and such, but we have children and I can't guarantee that they will always use them.

  2. lesley_ | | #3

    Does anyone else have thoughts? I have updated my design a little bit.

  3. Expert Member
    Akos | | #4

    There is nothing wrong with larger ducts. Important part is you want either flex runs with a lazy S bend or in-line duct silencer for the bedroom fresh air feeds.

    You might also want to have a run of flex between the ERV and both supply and return, this helps with the blower noise. Supply and stale air pickups inside conditioned space don't need to be insulated.

    For the outdoor connection, I would stick with whatever size the unit accepts. The only time you need to upsize it if it is a complicated run. Make sure to insulate the outdoor connections and seal the vapor barrier for the insulation to the collar on the unit with tape.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |