Author Topic: wiring an hrv for low speed with furnace fan  (Read 2061 times)

Offline oldguy2

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wiring an hrv for low speed with furnace fan
« on: June 13, 2016, 06:55:48 PM »
need help not sure if I need to buy a relay coil for this. I need to wire the hrv to turn low speed fan in the furnace on.the heat speed being used is perfect for the right temp rise and my cooling speed is a higher speed. fan on from t-stat is the cooling speed so I cant put my low speed fan wire on that tap this is a psc motor I need the lowest speed for the hrv costumer is bitching that the higher speed which is the cooling speed is to noisey and then shuts hrv off then complaines about moisture on windows. if I do need a relay for this which one do I get and how do I wire it to the low speed on furnace fan. ty

Offline Admin

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Re: wiring an hrv for low speed with furnace fan
« Reply #1 on: June 14, 2016, 03:12:48 PM »
What's the model of the HRV?  Most come shipped with an interlock relay already.  Be sure to use the 3 wire method instead of the 2 wire method or you could backfeed the AC.

Other HRV's sell an addon relay to interlock the HRV with the furnace fan.

You may see NO, NC and C terminals on the HRV.

Remove G from the furnace board, coming from thermostat, and marrette together with NC from the HRV.

Wire the NO from the HRV to R terminal on the furnace board.

Wire the C from the HRV to the G terminal on furnace board.

But in your case you don't want to energize the high speed furnace fan.  That makes things complicated.  We have to figure a way to energize the low speed fan but ensure no other fan speeds are energized during a call for heating or cooling.  The only way to do this is to interupt a call for heating or cooling when the HRV is on.  That could be problematic.

Does the client not complain about the high speed fan noise when the system is cooling?

If the heating speed produces enough CFM for cooling than I would connect that fan speed to both the heating and cooling terminals on the furnace board.  I usually cut the cooling speed and heating speed wires about 6" from the terminals on the furnace board.  Then strip the end of the heating speed wire coming from the fan motor and marrette it together with the hearing and cooling wires attached to the furnace board.  That way when G is energized, by the HRV or thermostat, it will energize the heating speed.  If the client is okay with the heating speed noise, than just leave it as your heating, cooling and continous fan speed.  Just marrette the end of the low speed and high speed wire coming from the motor, as they will no longer be used.

Also how is the HRV controlled?  The client seems to think the high speed furnace fan is causing the HRV to turn off sooner.  Most HRV controls are always on or always off or offer timed intermittent operation.


Offline oldguy2

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Re: wiring an hrv for low speed with furnace fan
« Reply #2 on: June 14, 2016, 05:10:42 PM »
furnace is a keeprite 93% psc motor the board has no continuous fan tap . yes the hrv has the interlock conections the problem is another heating company told the home owner that the cooling speed should be on high the blower is for a 5ton system but only has a2.5 ton ac installed I had the fan at a med speed told the home owner to call back other company cuz i'm not playing this game when other heating guys change everything around on the units. but I still need the low speed for the hrv heat speed is a med hi its an 80'000 btuh my temp rise was 55 if I lower the speed my temp rise will be to high.when the hrv is in use it energizes the cooling tap theres got to be a way to use the lowest speed for hrv  ive been thinking of using a 120 volt relay but been trying to figure out the wiring scenario lol