HRV furnace interlock help.

check the manual.

should involve connecting an output from the hrv to the g terminal. do it wrong and it may backfeed through the stat to y and bring on the a/c if you have it.

running the fan with the hrv is wasteful and uncessary if it draws stale air from a dedicated vent.

This is a terrible way to install an hrv:



..if it's done that way i urge you to change it rather than doing an interlock. the furnace fan may draw something like 300-500w.

with the hrv pulling air directly from the house, not a return it will ventilate just fine without the blower running.

If you have no hook up and feel brave, you can always add a relay across the hrv blower motor which would activate the furnace blower. You would however have to open up the hrv and in doing so, void the warranty.

If you don't want to void the warranty probably the best thing to do would be to turn the furnace fan on with a differential pressure switch. You would mount the switch at the hrv and as it starts it causes a pressure difference in the hrv line which in turn activates the furnace fan.

The red and green wires would connect across the NO contact on the pressure switch and the positive/negative pressure lines would connect near to the hrv on the fresh air side.