PSG Caddy with Electric furnace

[Steelerguy]

Long Time Reader First Time Poster,

Last year I replaced my Oil furnace with a PSG Caddy w/blower. worked great except when we left for the weekend and loading it up at 4:am.
So this year I added a 5 tone electric heat pump furnace.
This is working great for days we need a little heat and don't want to make a fire.
As winter approaches, I want to run the Caddy when I can and have the Electric furnace kick on when the fire dies out or I am not home.
I have the both furnaces cold air returns trunked.
I have dampers on both
The Caddy has an 850CFM fan
The Electric has a 1700 CFM fan

I have been told running both at the same time will put damaging stress on the fans.
Static pressure ?
So what I "think" I need is a relay that when the Caddy's Fan is running the Electric will not turn on.

So is there a relay that will satisfy this scenario?
Are there better ways to accomplish this?
Pictures and or additional details can be provided.

 

[brenndatomu]

So what I "think" I need is a relay that when the Caddy's Fan is running the Electric will not turn on

Welcome Steelerguy!
I would think that by the time the electric heat needs to kick on, the Caddy would be about burnt out and the blower would be cycling on/off, if even running at all. I am thinking that you need to wire the power for the Caddy fan through a NC relay (with a 120V coil) that is tied to the electric heat blower, when the electric blower kicks on, that will trigger the relay, turning off power to the Caddy fan. Even if the Caddy had a few hot coals that are still giving off a lil heat, things should be fine for the few minutes that the fan is "turned off"
You could even put a relay on both blowers so that that which ever one is running first, keeps the other from coming on until the first is off. Actually, I would use the second relay to open up the tstat wires on the electric heat though...don't want the electric coil coming on with no way to cool it.

The Caddy has an 850CFM fan

I thought the Caddy fan was more like 15-1600 CFM? I'm pretty sure it is way more than 850 (maybe 1850?)

 

[laynes69]

Psg carries an interlock that disables the central furnace when the woodfurnace is at a set temperature. If the temperature would drop from the woodfurnace, the central furnace can then operate to continue heating.