flashheatingand

We know why one is supposed to put the indoor coil on the supply side of the furnace. But, I was thinking that it may be better to put it on the return side if you are doing a hybrid set-up. The reason being is that frequently, the auxillary heat will kick in. If I am not mistaken, you really should not have the heated air go across the coil. With the coil on return side, the auxillary can kick on and the system would work like a champ.

Granted, humidity really isn't a big issue here (Boise), perhaps in the some of the more humid regions, the condensate on the H.E. would be quite detrimental.

Any opinions?

MechAcc

The system will still only pass as much air as the coil will allow to pass.

With the correct duel fuel kit or Vision Pro Thermostat there should not be a problem with the coil installed on the discharge side.

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snapperhead

i would mount the resistance heat on top of the coil and keep that fan with its positive air pushing thru the AC coil instead of it being a negative with it on the return.

palacegeo

We have done this when adding a split geo heat pump to an existing forced air unit. Then the geo and the gas can run at the same time when back up is needed.

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flashheatingand

The problem with the v.p. t-stat is that unless you set the cut-out compressor at 35 degrees, it is likely the gas furnace will operate simultaneously with the heat pump. Thus, 140 degree air is going across the "condensing" coil.

Also, the home owner cannot take advantage of the programable t-stat because the aux heat will kick in when the temp difference is more than three degrees.

flashheatingand

Maybe I am just talking to myself which is nothing new...) But seriously, I wonder what is the best way of installing a duel fuel/ hybrid setup. As mentioned earlier. If the coil is on the supply side of the furnace, it is likely that both the gas and the heat pump will operate simultaneously which isn't good. If there is a way to cut-out the hp when the gas operates and get the most use of the heat pump, I would like to know. I know you can set the compressor to cut out at 35 degrees, but that still doesn't guarantee the desired results. It would be nice to run the hp at any temperature.

I think the best solution is to put the coil on the return side, it's good to hear that someone else has taken this into consideration. I don't need to be right, I just want to do what is best.

flashheatingand

why do you say that? My thinking is that it really doesn't matter if the coil is sucking air through the coil or blowing through. As long as the airflow is the same, it's all good. Not looking for a debate, just curious to know your reason.