Connecting Honeywell T10 thermostat

andirocks

Hi,
I have a Bryant furnace with a humidifier attached which is controlled by a Bryant Tstatbbprk01-b thermostat.
The Bryant thermostat is starting to fail...losing time and not commanding furnace to fire.

I want to replace it with a Honeywell T10 but I'm unsure about a couple of the connections.

On the old thermostat there is a blue wire going to "DEHUMIDIFY" and a green wire going to "HUMIDIFY" where would these go to on the Honeywell thermostat?

Please see attached photos of my furnace manual with current wiring and photo of Honeywell terminals.

Thanks in advance,
Scott

Ironman

On the “UU” terminals.

andirocks

Does it matter where each wire goes? Are both U terminals providing the same function?

Thanks,
Scott

ratio

The U terminals are just contacts. According to the picture above, you need to send power down that green wire. I think that the T10 may have a switch to do that, or else install a small jumper wire from the R terminal to one of the U terminals, doesn't matter which. Land that green wire on the other.

Keep the red & white in the four wire separate (they land on the S terminals, one under each S) as they go to the outdoor sensor. It's possible that the outdoor sensor will need to be replaced, as it might not be compatible with the T10

andirocks

ratio,
It looks like the dehumidifier is pulling the 24 volts from the COMM in the furnace...or am I reading the diagram wrong?

ratio

Correctish. That's the 24VAC return terminal, AKA C or COM. The R terminal is the 24VAC supply. THe U terminals can be used to switch the power from the R terminal—once it gets to them. Again, there might be a switch in the base to do that, or a jumper will always work.

It looks like you can either dehumidify or humidify with that stat, but not both. If your Bryant's like the furnaces I'm familiar with, the dehum terminal just slows down the fan a little, which results in the AC taking a little more moisture out of the air. IIWM, I'd skip the dehum & use the U terminals for the humidifier, as that'll make a bigger difference in the winter than dehum will in the summer, assuming you keep it set reasonably & don't try to set back the cooling temps too far. If you really want to keep both, you'll need a separate (de)humidistat, for one function or the other.

The Honeywell 8000 (& I believe 9000) series will operate a wireless relay board (called an EIM) that has three sets of U terminals, it can be programmed for both functions, if you want to keep it simple(ish!). That's probably what I'd do, actually. I'm not a suuuper big fan of the T series stats, they just seem to be too complicated in some parts and too simple in others.

andirocks

Ratio,
So the COM is like a ground and R is hot. I took a quick look thru the furnace manual and the dehum terminal works as you said by running the fan at a lower speed for a period of time.

I agree I would rather have the humid for winter as far as AC room temps we usually keep it around mid 70's during the summer.

The T10 does have a couple switches one for R and the other for U. If I set both sliders up ( one wire) will that provide 24v to the U terminal to run humidifier? (see attached pdf)
Other wise I could pig tail a couple wires off of R before I attach that wire to thermostat.

Installing the EIM would be a bigger project than I want to tackle.

Is the outdoor air sensor really needed? If all it's doing is providing outdoor temp and humidity on a display for me to read I don't see the need for it.


Thanks for all your help!

Scott

mikeapolis

It's a good idea having the outdoor sensor for temp and humidity, it can keep your windows from sweating.
How old is the furnace?

andirocks

Best guess 13 - 15 years old...will probably need a replacement in the next few years.

ratio

The U switch does indeed provide power to the lower U terminal, so you'll land the green in the 4-conductor cable on the UPPER U terminal & program it for humidifier output.

The outdoor sensor isn't strictly necessary, but as @mikeapolis mentioned, (I think) the stat can be set up to manage the indoor humidity to prevent windows sweating in the winter time. Since it's already there, I'd at least try it. BTW, it will only show (drybulb) temperature. It takes a wireless REDlink outdoor sensor to get a local outdoor humidity, but I'm pretty sure the Internet connected T series can get a number from the internets.

andirocks

@ratio
I will give the outdoor sensor a try. The reason I asked about it is because my current thermostat is showing an outdoor air sensor error. I will have to follow some wires to find where the sensor is actually located and replace if needed.

Thanks again for all your help on this...greatly appreciated!!