I am working on a retrofit installation of an ERV. It is going to be connected to the return side of the furnace for both the return air and the fresh air supply. The exhaust is on the same side of the house as the exhaust of the furnace, so I have concerns that a backdraft may cause the CO to be pulled into the house when the ERV unit isn’t running and the furnace blower unit is running. The exhaust vent has a backdraft damper built in, but it is not very airtight. The vent is Broan Nutone 641 (https://www.supplyhouse.com/Broan-641-Model-641-Aluminum-Wall-Cap-for-6-Round-Duct-Natural-Finish). The furnace exhaust is still more than 1 meter from the erv exhaust, so perhaps it is good as it is. Is there a need for an extra backdraft damper?
As a background, I was thinking I could add a motorized damper just in case, but I am running into difficulties with creating the relay circuit for both the damper and the furnace blower. There is a timer control with furnace interlock (Soler&Palau SFM timer control), but it will only allow me to turn on the furnace fan, no separate relay switch to open the damper. I had difficulty with finding a relay with two separate switches that would be activated by the timer control (Soler&Palau SPTL timer control).
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