Thermostat/Blower question for HVAC experts...

[CountryBoy19]

Ok, I'm no retard when it comes to HVAC, but I'm not expert either and I have a question that I just want to double-check on.

I have an electric furnace but I supplement my heat by burning wood. To help circulate the air from the living room where the fireplace is in the winter I typically just turn the blower to "on" and I put a snap-disc thermal switch in-line with the fan blower so that the fan runs when the fireplace is hot. However, the problem is that doing it this way the blower won't run when the fireplace isn't hot so it doesn't really work as a primary/secondary system, it works as fireplace OR electric heat.

I want a way to run the fireplace as my primary heat and electric as secondary. So I determined that if I wire the snap-disc switch to run the fan independent of the rest of the system I could accomplish what I desired. I'm just not familiar enough with the way thermostats work to know 100% that my method will be acceptable.

I am guessing that I should be able to wire the snap disc switch between the R (transformer power) and the G (fan control wire). When the snap-disc closes power will be supplied from R to G and turn the fan on.

My question is this: Will supplying power create a backfeeding problem with my thermostat through G? Or will the power supplied to G from R be a problem in any other way? (IE, does the thermostat somehow change the voltage/signal to the fan control or is it simply a contactor that closes and transmits the voltage of R to the control circuit?)

Any help/insight?

 

[scott delaney]

Ok, I'm no retard when it comes to HVAC, but I'm not expert either and I have a question that I just want to double-check on.

I have an electric furnace but I supplement my heat by burning wood. To help circulate the air from the living room where the fireplace is in the winter I typically just turn the blower to "on" and I put a snap-disc thermal switch in-line with the fan blower so that the fan runs when the fireplace is hot. However, the problem is that doing it this way the blower won't run when the fireplace isn't hot so it doesn't really work as a primary/secondary system, it works as fireplace OR electric heat.

I want a way to run the fireplace as my primary heat and electric as secondary. So I determined that if I wire the snap-disc switch to run the fan independent of the rest of the system I could accomplish what I desired. I'm just not familiar enough with the way thermostats work to know 100% that my method will be acceptable.

I am guessing that I should be able to wire the snap disc switch between the R (transformer power) and the G (fan control wire). When the snap-disc closes power will be supplied from R to G and turn the fan on.

My question is this: Will supplying power create a backfeeding problem with my thermostat through G? Or will the power supplied to G from R be a problem in any other way? (IE, does the thermostat somehow change the voltage/signal to the fan control or is it simply a contactor that closes and transmits the voltage of R to the control circuit?)

Any help/insight?

to be able to do what your wanting to do.....from one to another.....with out rewiring things every time change back and forth from elec to fire place you will need to wire in a double pole double throw relay....other wise you will have to switch wires back and forth. if you give me a run down of your set-up i can draw you up a diagram to wire it with out moving wires

 

[Woodsman]

Find a two-stage heating stat. First stage is for blower & wood heat, second stage is for electric heat, or some variation that accomplishes the same thing.

 

[CountryBoy19]

to be able to do what your wanting to do.....from one to another.....with out rewiring things every time change back and forth from elec to fire place you will need to wire in a double pole double throw relay....other wise you will have to switch wires back and forth. if you give me a run down of your set-up i can draw you up a diagram to wire it with out moving wires

4 wires to T-stat
2 wires from snap disc (in fireplace) to air-handler (right where other t-stat wires enter air-handler)
2 wires to condenser outside

A/C with Elec heat (single stage) + fireplace in living room, currently isolated from HVAC system.


Are you saying that it will cause problems by connecting R wire to snap-disc and snap disc to G wire? Is that a t-stat issue or control/signal issue with the voltage on R?

Let me try to explain what I'm trying to do in more detail.

There are 6 wires that exit my air-handler and are connected to the t-stat wires with wire-nuts. 2 wires go to the condensor unit, 4 wires go to the thermostat. Of the 4 wires that go to the thermostat there is a red wire (transformer) and green wire (fan control wire). It is my understanding that the thermostat signals the fan to turn on by connecting R to G (I can't see why the t-stat would change the R voltage when connected to G other than normal line-losses). I plan to undo the R & G wire-nuts at the air-handler and add in a third wire to each connection that will also connect to the snap-disc. So then I would have 1 R wire coming from transformer then splitting off to go to both the snap-disc and the t-stat. I will also have 2 G wires, one from t-stat and the other from the snap disc returning to the air-handler and connecting to the single G wire that enters the air-handler. It is my understanding that should either R wire be connected to the respective G wire, the air-handler will turn the fan on. Correct?

So the only thing I can see that might be a problem is that when the snap-disc connects R to G, the G wire connected to the T-stat will now be energized. Could this cause a back-feed issue with the t-stat? If it's just a simple relay inside the t-stat then I can't see how back-feeding will be a problem. However, if it is a transducer inside the t-stat then backfeeding may be a problem but I'm not sure, it's been a few years since I've dealt with transducers and I can't recall the characteristics.

If it helps, there is an audible click when my t-stat kicks the a/c on which leads me to believe that the contacts inside the t-stat are relays as opposed to transducers.

 

[CountryBoy19]

Find a two-stage heating stat. First stage is for blower & wood heat, second stage is for electric heat, or some variation that accomplishes the same thing.

Problem is, I want the fan to run the whole time the fireplace is hot but no more than that. IE, I want the fan to run when the snap-disc detects that the fireplace is hot and only then (unless electric back-up heat is running).

I can't think of a way to connect a 2-stage t-stat and accomplish this. T-stat is in the living room, same room as the fireplace, so when the room warms up it will detect that it no longer needs heat and it will shut down the fan. Not to mention that I only have a 4-wire t-stat wire and there is absolutely no way to run a new one unless I run it up into the attic, across the house then down through walls. This would be very complicated and a lot of wiring. I'd like to do it an easier way if possible.

 

[bman1962]

I'd just run the fan all the time by turning it on at the sub-base. I understand you want the energy savings of not running the fan any extra time than needed but I can't imagine it saving you much energy.
I've been a HVAC service tech for over 20 yrs. and I can't see making something any more complex than needed. Good luck to you.

 

[CountryBoy19]

I'd just run the fan all the time by turning it on at the sub-base. I understand you want the energy savings of not running the fan any extra time than needed but I can't imagine it saving you much energy.
I've been a HVAC service tech for over 20 yrs. and I can't see making something any more complex than needed. Good luck to you.

Is it really that complicated though? The wiring and switch are already in place; they were installed when the fireplace was installed last year.

I know that you can bypass the thermostat to turn the fan on by connecting R to G. So the only question is, will I harm the thermostat by connecting R to G while the thermostat is still connected to them?

And yes, it does make a big difference running the fan all day. Not only does it increase thermal losses when heat isn't being supplied by the fireplace, but it also draws a lot of juice. About midway through last winter I switched over from running the fan constantly to running it with the snap-disc switch and saw my electric bill drop from $300/mo to about $175/mo. It doesn't take much energy savings when your electric co-op is the most expensive in the state. I pay $.13/kwh in the winter, I don't really want to waste it on running the fan all day long.

The reason I need to get the system set up this way is because I'm not going to be here this winter so I want both systems to work together so my wife doesn't feel forced to bring wood in etc, and the house won't freeze when she is away.

 

[Anonymous]

If this is what you are talking about:

You will be fine.

 

[CountryBoy19]

If this is what you are talking about:

You will be fine.

Exactly what I'm talking about! Thanks for the diagram and answer, rep incoming!