Thermostatic Controls - Using a 2-stage gas furnace as dual-fuel backup with TH8320 thermostat

I have a Goodman SSZ160241 Heat Pump with a Goodman GMV950704CX 2-stage gas furnace for fossil fuel backup heat and a Vision Pro TH8320U1008 thermostat with outdoor sensor (8+2 sensor wires in the wall). It's obvious how to connect the standard 1H/1C wires, but ...

How should I connect the "E" and "AUX" terminals on my thermostat to the "W1" and "W2" terminals on my 2-stage gas furnace? Or do I need to jumper "AUX" and "E", connect both to "W1", and set the furnace to "single-stage thermostat" mode? Or is there yet a better option?

Also, should the "system type" (option 0170) be set to "7" (2H/1C+Aux) as there isn't a (1H/1C+Aux) option?

(Options 0200:1, 0210:0, 0340:2, 0350:30deg are set correctly.)

Or do I need to jumper "AUX" and "E", connect both to "W1", and set the furnace to "single-stage thermostat" mode?
Yes, this what you need to do for your system.

Or is there yet a better option?
Oh yes... See if the dealer can let you upgrade the t-stat to the Honeywell IAQ t-stat. The IAQ model is far better than the VisionPro.

Also, should the "system type" (option 0170) be set to "7" (2H/1C+Aux) as there isn't a (1H/1C+Aux) option?
Yes, set it to 7.

(Options 0200:1, 0210:0, 0340:2, 0350:30deg are set correctly.)
All but 350 looks good.. I'd change 350 to 15˚ and see how that works out, if you see that the HP falls behind, then bump it up to 20˚.

Set 360 to 40˚.


If you get the IAQ t-stat, you can then run the furnace on a true two stage vs timer.

Thanks, Jay. I commend you on the clarity of your answers!

What about the "W2" (the "in defrost") output from the HP? Does it just connect to "W1" to turn the furnace on during defrost?

(What common wire colors are used for "Aux", "E", etc., on the 'stat, and "W2" at the HP? I want to make it easy for the next person to work on this system!)

What about the "W2" (the "in defrost") output from the HP? Does it just connect to "W1" to turn the furnace on during defrost?
Yes.

(What common wire colors are used for "Aux", "E", etc., on the 'stat, and "W2" at the HP? I want to make it easy for the next person to work on this system!)
There is no "code" for colors, just whatever is left. Most of the time it's

W-White
G-Green
R-Red
C-Blue
Y-Yellow
W2/Aux-Brown
E-Black

Are you keeping the VP or are you going to upgrade to the IAQ?

I'll keep the VP till I find a "really good deal" on an IAQ. (I only paid about $100 for the VP with the outside sensor, no trade-up option available.)

Or after the next heating season, when I have an idea of what the "real" crossover outside temp is for the HP I may just add a mechanical outside stat to switch from the HP to Furnace (aka "fossil fuel kit"), then I can run the furnace as a true dual-stage.

(Unfortunately, when I was evaluating 'stats before purchase I thought that the significant differences between the VP and IAQ was "humidity" and "only 3-wires to stat".)

(Unfortunately, when I was evaluating 'stats before purchase I thought that the significant differences between the VP and IAQ was "humidity" and "only 3-wires to stat".)

As we already talked about in our e-mail, IAQ is more than that.

I'm sure you can sell the VP to a friend or family member who don't have high end equipment.