Can I install two thermostats to control one furnace?

Thanks Doug and Fred. This is what I tought, all the functions of the furnace should not be affected and everything seems to work as before. I do not know which and where I would connect the new T-stat directly to the furnace.

The living room T-Stat ONLY will control the ON/OFF of the furnace, the new room T-stat is only a heat on/off to fool the front one, like a check point in line saying "hey wait until it is cold here to kick on".

I do have two factory T-stat installed in the MH, one in the living room and one in the room. The living room operates the Front AC and/or fan and the furnace. The room T stat control the Rear AC and/or fan only, not the furnace.

The rear one does not control the furnace but all the wires are connected to it like the front one. I wish I could have used this rear one to control the furnace also but really do not know how I could do it. Maybe it would be easier to try to connect the rear one to control the furnace also?

As for the very tiny wires that connects in the T-stats, I did not see where they connect to. They are different size than the one connecting at the furnace plug. The furnace one are normal gauge wires like 16 or 18 gauge I guess. If I could find the tiny one in the basement or somewhere, maybe I could Tap these one to operate from the rear instead of using a new T-stat.

Any advices on this is appreciated.

Kidoo wrote:
I have 2 pamphlets with the MH. One says Atwood 8500-IV series and another one says 2 stages furnace.

I will check for the wires and what it says on the furnace, but I am pretty sure I saw 2 grey wires. For sure I have 2 whites and one red and ? grey.

If I disconnect one of the white wires while the furnace heat is on, the heat stops and the fan keeps going.

The Heat Stops because the limit switch is closed. Once the Chamber cools down, the fan will shut off. Doug

doxiemom11 wrote:
Our Monaco does doug. We can use either of them for the furnace or for the AC. For the AC - the AC in the bedroom is controlled with the bedroom thermostat, and the one in the living area controls the AC in the living area. Both thermostats are identical with on/of, heat/AC and a temperature setting and a fan only setting with hi/lo choices. They are Dometic thermostats. We have used either/both for the furnace so we know for a fact that they work that way.

Then you have 2 furnaces. You cannot and Monaco never wired 1 furnace to 2 tstats. OR, you have an Aquahot system, which is NOT a furnace. Some OEM's installed the same model tstat in the bedroom and living room and even tho they state Heat, does not mean that they control the furnace. Doug

Kidoo wrote:
Doug, you are right, there are only 4 wires. From the RV side of the plug to furnace, there is One red, two whites, one grey. On the other side of the plug, the Furnace side when you look inside the furnace from the outside door, there is 4 wires: One red, two blue and one yellow.

I just want to make sure I can do the extra stat without compromising the safety aspect of the furnace. But from what I understand, I did not altered any of the function of the furnace, just made a disconnect like I would do with a switch.

The way that you wired in the second thermostat, it is safe.

What I would have done is connect the second thermostat directly to the furnace, so that either thermostat can call for heat, and turn it on. Both thermostats in my case would need a 'off' switch, or it might come on while the RV is in winter storage or if the coach gets below say 50F while not out camping. In your wiring situation, the 'off' position of the front thermostat would shut it off completely. (yet make sure by trying to turn up the rear thermostat while the front one is off. As long as the furnace will not start, you will be fine.

Have fun camping!

Fred.

Our Monaco does doug. We can use either of them for the furnace or for the AC. For the AC - the AC in the bedroom is controlled with the bedroom thermostat, and the one in the living area controls the AC in the living area. Both thermostats are identical with on/of, heat/AC and a temperature setting and a fan only setting with hi/lo choices. They are Dometic thermostats. We have used either/both for the furnace so we know for a fact that they work that way.

Doug, you are right, there are only 4 wires. From the RV side of the plug to furnace, there is One red, two whites, one grey. On the other side of the plug, the Furnace side when you look inside the furnace from the outside door, there is 4 wires: One red, two blue and one yellow.

I just want to make sure I can do the extra stat without compromising the safety aspect of the furnace. But from what I understand, I did not altered any of the function of the furnace, just made a disconnect like I would do with a switch.

I have 2 pamphlets with the MH. One says Atwood 8500-IV series and another one says 2 stages furnace.

I will check for the wires and what it says on the furnace, but I am pretty sure I saw 2 grey wires. For sure I have 2 whites and one red and ? grey.

If I disconnect one of the white wires while the furnace heat is on, the heat stops and the fan keeps going.

Kidoo wrote:
Ok, thanks all for your quick responses. Wa8yxm thanks for your inputs, I went and checked the wires going to the furnace, there are actually 5 wires in there. A 12 volt, two white and two grey. I disconnected a white wire that controls the furnace, if this one is disconnected, the heat and eventually the fan will stop after all the heat is dissipated. There is another white wire that controls the heat only, if I disconnect the second one, the fan only runs but not the heat.

So, I installed a bi-metal T=stat in series with the white wire that controls the furnace On/Off. Actually cut the white wire and connect it to the new T stat, one end to one screw of the T stat, the other to the other screw.

Now, for Room heat, I put the living room furnace switch on and at full heat. I then put the switch ON on the room T Stat witch will make the continuity but only if the temperature lever on this new T stat calls for heat. When the room temp reach the room T stat preset, it cuts the power to the furnace. The furnace finishes it's cycle and shuts off.

For living room heat, I keep the room T stat ON and at full heat, and the living room T stat ON, but this time, the living room T stat has the controls, it will shutt off the furnace once the living room is at temp.

Looks like it will work? The grey wires, I do not know what they are used for but If I disconnect them, the furnace completely stops, fan and heat, so I do not touch these ones.

Any advices?

Please respond with the brand and model of your furnace. Monaco used both Atwood or Suburban and NEITHER have 5 wires. They have 4 wires. Unless you have the 2 stage Atwood but that would require the Atwood wall tstat and usually Monaco did not install this model Atwood furnace. Doug

." I disconnected a white wire that controls the furnace, if this one is disconnected, the heat and eventually the fan will stop after all the heat is dissipated. There is another white wire that controls the heat only, if I disconnect the second one, the fan only runs but not the heat". Unless someone has modified your system (or you have the 2 stage Atwood) there is NO such control or wiring on an RV furnace that will allow the Furnace fan to run and not start the Burner. Doug

doxiemom11 wrote:
We have two thermostats and only 1 furnace. We never have both turned on for the furnace - reason being, the furnace would run almost constantly between the two locations calling for heat and when it does run, heat comes thru every vent anyway just like it does with only 1 turned on. What are you trying to accomplish by having 2 hooked up? If you want to bump it up from in bed in the morning before getting up to let it warm a bit first, that would work as long as you later turned 1 of them off.

You have 2 tstats and only one furnace. BUT, only 1 of those tstats controls the furnace, usually the front living area tstat. NO RV has 2 tstats that control 1 furnace. Doug

One note, the T stat I used is a Camper Bi-metal T stat, so it has the On/Off switch and the temp control lever.