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Like many others, temperatures between the two levels of my house are uneven. This is particularly noticeable as spring arrives and the upper floor (above ground) enjoys solar heating (so the heater never runs) and the lower (in ground) floor cools off. Frequently, I manually turn on the furnace fan at the thermostat to circulate air between floors and this basically achieves the goal. But then I forget to turn off the fan override. So, I'm wondering if I can install a second thermostat on the lower floor to automatically control the heater blower only when the temperature falls below a given threshold on the lower floor.

Givens: 1) I have a recent model high efficiency natural gas heater 2) my current Thermostat is Honeywell TH4110D1007 Programmable Thermostat 2) access to the heater on the lower level is trivial


1) I can add a second thermostat in parallel

2) I would only make some connections from the new thermostat

3) 24v Power is supplied with the Red wire

4) Heat is controlled with the White wire

5) Fan is controlled with the Green wire

6) I'd be using a simple programmable Honeywell thermostat

7) I'd need to manually set similar time periods and temperatures as are set on the existing "master" thermostat.

Note: In my current plan, I am NOT trying to turn the heating on - just the fan.

So, my specific questions:

A. Has anyone ever done this?

B. Would I connect the Fan wire or would I actually cross connect the thermostat's Heat connection (W) to the fan control wire. i.e., to get automatic fan control, would I use the G or W wires to signal/control? Or, am I totally mixed up?

C. Am I risking my entire system for something risky?

D. Is there another better way to achieve the goal?

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possible duplicate of Can I pair two thermostats to work with a single zone system? – Comintern Apr 13 '14 at 21:41
Perhaps, but I didn't think so. As I understood the earlier question, they are trying to control temperature from a second location which might drive first location off target and I'm only trying to control the fan from the second location. Also, running a wire from new to old location would be much more difficult than what I have in mind. – Karl G Apr 13 '14 at 21:47
I use a second Tstat to run the fan in my solarium if it gets too hot (that's part of a dual system house); it calls for AC but it's wired to the fan, which helps bring the hot air down from upstairs, as it's return is on the middle level. Note however, my T's run on batteries; not 24v. – Mazura Aug 17 '15 at 20:05

Some thermostats already include a fan "recirculation" mode, which runs the fan for (usually) ⅓ of the time that the thermostat is NOT calling for heating or cooling. This feature is specifically to mix the air in the dwelling so the temperature remains even.

I recommend upgrading your thermostat to one with this feature.

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