Controlling Oil and Gas Furnaces with a RTH9580


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Old 04-19-22, 10:22 AM
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Controlling Oil and Gas Furnaces with a RTH9580

I have my Clean Burn used oil furnace running on my Honeywell RTH9580 wifi thermostat. I stole 24V from my gas furnace for power (controlled by a mercury thermostat. I may have it wired wrong, but it works fine.

I never figured out how to move the control for the gas furnace over to the Honeywell thermostat as a back up or alternate heat source. The image shows the current wiring of the two thermostats.

It would sure be nice for this old guy if someone who know could just tell me where to locate the Gas Furnace wires on the RTH9580.

Thanks a Bunch!




 
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Old 04-19-22, 01:31 PM
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Welcome to the forums.

Not sure connecting two heat sources is going to work out for you.
Primary heat with a heat pump and backup or emergency heat is common.

No real way to control two separate heaters. I don't believe there is an emergency or backup heat option in conventional mode.

What is the "junction" you are showing ?
Where is the C coming from.
 
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Old 04-19-22, 02:26 PM
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The "junction" is just a box with the wires connected in it.
The C is 24 volts from the Gas Furnace to power the RTH9580 thermostat.

I guess I didn't realize that a gas furnace and heat pump combination may have been much different than what I had in that the heat pump could deliver a demand for heat. I thought maybe I just had to figure out how to deliver that demand

Thanks
 
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Old 04-20-22, 06:28 AM
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Hi, so you would be be using one or the other and not both at the same time, correct? What is your connection at the gas furnace, interested in a manual switch over? possibly.
Geo 🇺🇸
 
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Old 04-20-22, 02:32 PM
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I use the oil primarily, the gas is only if I run out of oil or have a problem with the furnace.

At the gas furnace, the connections are only to W and R.
We have a newer RTH9580 at the house, and it shows an "emergency" under system. I don't touch that one, my wife is the chief operator I think it uses the heat pump as primary heat and the gas furnace as secondary, the gas could be the "emergency".
If that is the case, I would have thought that the thermostat would have two terminals which would signal a demand for heat, one for the heat pump and one for the emergency/gas.
 
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Old 04-20-22, 03:19 PM
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I think it uses the heat pump as primary heat and the gas furnace as secondary, the gas could be the "emergency".
Yes....as I previously mentioned.... that is how it works. However you aren't using a heat pump.

With a heat pump.... the compressor running as a heat pump is primary heat.
W1 is the AUX or backup or E heat.

When you set the stat to normal/conventional operation.... there is no AUX or backup or E heat choice.
 
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Old 04-21-22, 09:40 AM
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I must say, this is definitely an interesting setup, you must have 2 power sources to that stat, or am I missing something?
Geo 🇺🇸
 
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Old 04-22-22, 08:37 AM
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I think I would use a relay for the oil furnace, and wire the gas furnace to use the W2 terminal. Of course this means you may have both furnaces kicking on when it gets really cold.
 
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Old 04-22-22, 07:19 PM
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Geochurchi
The only power source is the Blue wire from the gas furnace thermostat.

caddymac
The only purpose of the gas is as a backup in case of oil furnace failure, I don't know that it would be a problem if they both ran in real cold conditions. There is not an outdoor sensor of any kind hooked into the system.

Thanks
 
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Old 04-23-22, 01:33 AM
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You have two 24v power sources.... oil furnace via TT and the gas furnace.
The power for the stat is coming from the gas furnace so that must be the primary heat source.

You may be able to wire the stat for heat pump operation. Gas is primary.....oil is E heat. The blower can only be controlled to the gas furnace via G. Technically the G is not needed as the furnace will turn on the blower.

gas furnace......
B/C -------------------> C
W ---------------------> Y
R ---------------------> Rc (R jumper must be unplugged)
G ---------------------> G

oil furnace ...........
T1 -------------------> W2/AUX/E
T2 -------------------> R

That stat doesn't have many programmable options like some of the more sophisticated ones do.
This would be strictly experimental.
 
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Old 04-23-22, 08:12 AM
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Hi, just curious! If these are both furnaces, are they ducted together?


Geo 🇺🇸
 
 

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