Interlock Relay Wiring


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Old 09-05-09, 08:03 PM
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Interlock Relay Wiring

I'm in the process of installing a EPA Wood furnace in Parallel with my current propane furnace. Its a older miller 90% furnace. I have my damper motor for the wood furnace and the limit control along with the thermostat wired. I can't for the life of me figure out the Interlock for the system. Because both share the same return air supply, I don't want both to run at the same time. I'm not sure if I need another limit/control on the plenum of the woodfurnace to control the propane furnace. I just can't figure out where to wire on the propane furnace, because it operates with a snapdisc.

http://www.noutilitybills.com/Furnac...lOilManual.pdf

Page 18 is what I am thinking, but like I said I can't figure it out on the propane side. Any help would be appreciated. The gas heat runs through the plenum of the woodfurnace. Don't want that tripped when the woodfurnace isn't being used.
 
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Old 09-05-09, 08:26 PM
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not real sure I am understanding what you are doing so maybe if you answer a question:

for sake of explanation only:

would simply having only one unit on at any given time be all that you are trying to do?

or is there some other action needed when one or the other runs?

and if the answer is yes, is there one that would have priority to run over the other?
 
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Old 09-05-09, 08:33 PM
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Yes, I mainly want one side at a time, not both. Lets say the propane furnace is running and not the woodfurnace. The heat of the propane will trigger the limit/control in the woodfurnaces plenum. When that fan runs because of a call for heat, it will turn on the woodfurnace blower and cool the air from the propane. I probably could turn off the woodfurnace when using only gas, but the furnace came with an interlock, which thats where im stumped. Both contain a thermostat the woodfurnace and the gas furnace. I will set them about 5 degrees apart. That way if the wood dies down, the gas kicks in and heats the house.
 
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Old 09-05-09, 08:56 PM
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without getting too simplistic.

what if you controlled a relay with the t-stat call for the gas unit so that it would interrupt the power from the high temp fan on sensor of the wood unit.


what this would do is;

allow the wood t-stat to run the wood unit fan until such time the gas unit was called into action. Then, it would prevent the wood unit from running it's fan.



too simplistic? not the proper sequence of control you are intending?

the thing that would worry me about this arrangement would be the possibility of too much heat build up in the wood burner that should be cooled down. This could be rectified by using a added Klixon that would over ride the controls above and run the fan for the wood burner regardless. Not sure if this would be needed but just something that struck me as a possible need.
 
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Old 09-05-09, 09:09 PM
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Thats what worried me about the heat buildup also. With a potential of 140,000 btus from the woodfurnace it could go bad quickly, because of a custom damper over the woodfurnace to isolate it from the gas furnace. The way the interlock was explained is it would shut down the gas furnace if the plenum temp in the woodfurnace hit 150 degrees. Which is fine to keep the heat down in the ductwork. Maybe I will let it be for now and rethink it later. I can just flip the switch on the woodfurnace off if its too warm for a fire, but heat is needed in the home, and come winter flip that switch on. My last furnace was series, so much easier.
 
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Old 09-07-09, 06:49 PM
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After some thought I better install the interlock. Both can run at the same time, but with the interlock the gas will shut down or not run if the woodfurnace plenum temps reach 150 degrees or more. This is for safety reasons. Here is a simpler link, I just need to know where the red and black wires lead to on the propane furnace from the interlock/relay . Page 19.

http://www.psg-distribution.com/forc...6112008763.pdf

Hopefully the link works. It shows the burner relay, but where on the propane furnace? I'm not an electrician, but have wired alot of things, this has got me stumped. Its the 2nd part down on this link.

http://www.partsguy.com/pdf/8A04-1.pdf

One other thing. If I install this, and the gas furnace hits 150, wouldn't it shut down the furnace, or will the gas furnace be okay if the thermostat is calling for heat?
 
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Old 09-07-09, 07:15 PM
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can you post the model of the furnace (old unit) or better yet, post a link to the schematics of the furnace
 
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Old 09-07-09, 07:20 PM
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http://i295.photobucket.com/albums/m...9/manual-1.jpg

Furnace is close to 20 years old, but has about 5 years of use on it due to woodburning.
 
 

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