HVR retrofit into a townhome hvac system
Hi
I have a townhome that I’d like to retrofit an HRV into. The furnace room is interior without any exterior facing walls and it’s unlikely I’d be able to get the association to allow me to run ducting to exterior walls or roof to provide an inlet and outlet for air. The townhome is 2 story with a bathroom on each floor and each bathroom has an exhaust fan that runs out through the roof. My idea is to splice the exhaust lines in each bathroom and make one roof vent an intake and the other the exhaust. I’d use existing exhaust fans in bathrooms to become the piping to run through the HRV and out one of the bathroom roof vents as exhaust air and I’d use the other roof vent for fresh intake to go through HRV and then into furnace ductwork.
What are your initial thoughts on this?
if I used insulated ductwork (cold Minnesota weather) would I have any issues with condensation inside of the ductwork dripping back down into the HRV and causing problems? What would be a solution to this problem?
Are there any obvious code violations with a setup like this?
Thanks for your help.
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Replies
Bathroom exhaust ducting usually assumes you are exhausting air that is close to house temperature. This generally means that the run inside the house is not insulated or if it is, it is not sealed well.
Both fresh air intake and stale exhaust on a HRV is close to outdoor temperatures, without a well insulated and sealed run, they will sweat.
If you can access the existing duct chase, you can run new ducts and only use the existing roof jacks.
Better options might be to run the duct out to a balcony.
Does the HOA carry "Walls-In" coverage? If not then you only need to get permission from the HOA for penetrations of the exterior wall.
Before you go any further have you air sealed the unit? Windows, Doors, 2nd floor ceiling penetrations?
When using the existing HVAC duct work for a HRV you want to use the duct returns for the exhaust rather than the bathroom vents.
Read section "Multi-Point HRV or ERV with Full Connection to Central Air Handler"
https://www.buildingscience.com/documents/information-sheets/info-611-balanced-ventilation-systems