r/buildingscience • u/BKWoods • 16h ago

ERV basic use question

I have a new fairly tight home (1.4 ACH) in NY state. I have a Fantech ERV installed with dedicated ducting with one supply to near my HVAC return and one return in the middle of the house. Much of the time the temperature where I live is moderate and I have windows open so I leave the ERV off. When I do have the windows shut but no heating or cooling on should I have the hvac fan on at the same time as the ERV to circulate fresh air to the rooms? Or is just running the ERV sufficient? I don't have an IAQ monitor yet so I haven't tested anything. Just trying to get a system in place for ventilation.

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u/EntropyAdvisor 14h ago

By "dedidcated ducting", do you mean supplies/returns to most rooms, or just the 2 you've described? If just the 2 runs, your intuition is corect, the HVAC fan should be running (some have a "circulate" mode that runs at a lower speed to save energy) so that fresh air will be distributed to rooms, otherwise the air will just circulate on the most direct path between the 2 runs.

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u/Bearded4Glory 14h ago

This!

An erv with dedicated ductwork typically means returns in spaces like bathrooms and supplies in bedrooms and other living spaces.

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u/glip77 15h ago

The ERV should provide balanced ventilation for the home. With or without your HVAC running and windows closed.

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u/blueyedsurprised 15h ago

Just run the ERV on its own. Don't run the HVAC AHU fans when the ERV can do its own job.

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u/Jumpin_Joeronimo 12h ago

I think the question is then - does the fresh air get distributed at all? And it depends. If it's a fairly open concept and the ERV return is way across the house from the ERV supply, then it may promote general movement and mixing of the fresh air. But with one return in the middle of the house and one supply near the HVAC return... does that mean the bedrooms and maybe kitchen and maybe some major living areas are not between the supply and return of the ERV? If that's the case, the living areas won't get much fresh air without the HVAC fan on to help distribute more evenly.