Electrical gurus....please come in

[JRHAWK9]

Currently my LP thermostat is set at 55° to keep it from kicking in when the wood furnace is running/still hot (so it doesn't back feed the wood furnace when the wood blower shuts off). I want to be able to set my LP thermostat higher so when/if we aren't around to load the firebox in very cold weather the two furnaces can run at the same time so the house doesn't have to lose temp in between loadings. Basically want to be able to use the LP furnace as sort of a helper furnace when it's ever needed between loadings to keep the house a steady temp. I currently have a 120V spring open/power close powered zone damper installed in the supply duct connecting the wood furnace to the existing duct and functioning (wired for summer AC use) but want to re-wire it to accomplish the above. They share the same supply duct but NOT the same return duct. The wood furnace has an open staircase for it's cold air return. I already have a gravity damper protecting the LP furnace from back feeding but want to protect the wood furnace from back feeding.

I have two independent 120V sources in which I can use as triggers to control the zone damper under different situations.

I have the following:
Trigger A (120V from LP furnace when blower is on)
Trigger B (120V from wood furnace when blower is on)

Here's the situation. I need the damper to NOT receive power (spring open) when both trigger A & B are powered AND when only trigger B is powered...BUT I also need it to receive power ( power close) when just trigger A is powered. Doing this should allow what I want to do w/o back feeding the wood furnace while still keeping for gravity flow in case of a power outage. Basically the damper will remain open the whole time except for when the LP blower is the only one running (in summer and winter), then it will close to prevent back feeding the wood furnace.

There has to be a way to wire something like this up with some relays, I'm just not smart enough to figure it out...lol Anybody know how to do this?

 

[Bret Chase]

that's pretty easy...

connect line a to the normally closed contacts.... hook line b to the coil.

this way, if B is off... A can power the damper. When B is powered, it interrupts A... so it doesn't matter if A is powered at that point.

make sense?

 

[JRHAWK9]

It does make sense, however, can you put it in a sketch using a NO NC 5 pin relay? I can understand pictures much easier and it's easier for me to go through the different situations. Where would the damper connect to then? I guess I understand in theory but don't know how to physically wire it up.

I figured it was easy...lol

 

[JRHAWK9]

OK, I think I figured it out. I just needed to see a photo to remember the connections. Is this correct?

1 & 3 (coil) gets 120V from the wood furnace blower (B).

5 gets lead from LP blower (A)

4 gets connected to damper (+).

 

[Bret Chase]

there ya go



Hook A to terminal 4, damper to 5

 

[JRHAWK9]

thanks! It's the same as what I posted as far as I can tell. However where you state "to blower" I think you meant "to damper"....correct?

 

[JRHAWK9]

there ya go

View attachment 153311

Hook A to terminal 4, damper to 5

OK, so is this correct?

1 & 3 (coil) gets 120V from the wood furnace blower (B).

4 gets lead from LP blower (A)

5 gets connected to damper (+).

 

[Bret Chase]

yes, to damper, not blower

you've actually got "A" and damper reversed compare to mine. whatever is switched should almost always be on terminal 2 (NO) or terminal 5 (NC)...

the N/C means not connected

 

[Bret Chase]

OK, so is this correct?

1 & 3 (coil) gets 120V from the wood furnace blower (B).

4 gets lead from LP blower (A)

5 gets connected to damper (+).

View attachment 153312

Yes.

 

[JRHAWK9]

thanks much!!

 

[JRHAWK9]

got it all wired up and it works like a charm. thanks again.

 

[bobdog2o02]

got it all wired up and it works like a charm. thanks again.

I'm a free standing stove user but I love seeing the follow up from the OP. Good stifstufff guys.