Setting thermostat differential to 3 degrees?

[max1234]

My heat bill was very high this month, even though it was warm for Iowa this year. So I first checked with my gas company; everything is okay there. Had my furnace installer guy come to the house. He installed my new Amana 96% two stage furnace and thermostat three years ago. After checking the furnace and the thermostat he figured out that the problem was that my differential settings at both the first stage and second stage (on the thermostat) were set too low; both were set to 1 degree. He said that made the furnace kick into high heat almost all the time, instead of using the low heat most of the time (therefore higher gas usage). We set both the differentials on the thermostat to 3 degrees. Does this make sense to you all? As I said my furnace is only three years old. The first two years the gas bills were very low, but I do admit to changing the differentials to 1 degree on the thermostat (because I don't know what I'm doing). Do you agree with my furnace guy that this is probably the reason why I used so much gas this winter? Oh, I forgot to say that my furnace guy said that when he first checked out my furnace that the heat was on 2nd stage (high) instead of normally being on 1st stage (low) and he was puzzled as to why it was instantly on high (this was before we checked the thermostat differential settings). Should I keep both the first stage differential and the second stage differential to 3 degrees? Or should one be higher or lower than the other?

[mayguy]

Yes, the furnace firing off on high fire right away, and with our mild midwest winter so far is making your furnace "oversized" in a way that it's short cycling on and off.

What is the make and model of the t-stat you got?

[max1234]

You asked: What is the make and model of the t-stat you got?

It is a RobertShaw 9615. I don't really like it. I would prefer a thermostat that tells if you're using stage 1 or stage 2 heat. Is there such a thing?

[mayguy]

You asked: What is the make and model of the t-stat you got?

It is a RobertShaw 9615. I don't really like it. I would prefer a thermostat that tells if you're using stage 1 or stage 2 heat. Is there such a thing?


If you want a good t-stat, I'd go with Honeywell VisionPro (http://www.hotfreshcool.com/visionpro_demo.html) TH8320, and if the installer is good, he put a jumper wire on the t-stat and lights up a red LED on the upper right corner when calls of 2nd stage. And if you have common wire, the back light can be on all times, sure a heck lot easy to see than that Robershaw!


Is the furnace varaible speed?

[max1234]

You asked: Is the furnace varaible speed?

Yes, it's an Amana 96% GUVA Air Command 2-stage, variable-speed gas furnace. I like that Honeywell display. You're saying that my installer can put a jumper wire on this Honeywill so the display will show a red light when the furnace kicks into 2nd stage heat? Yea!

The current RobertShaw thermostat had the first stage differential factory set at 1 degree and the second stage differential factory set at 2 degrees. I have increased these both to 3 degrees thinking this will keep the furnace from using the 2nd stage as often. Am I wrong?

[mayguy]

Yes, if he is good and knows how to make this work.

If you want humdity control on the A/C side of the system (Slows down the blower when humidity is high) you could step up into the new Honeywell IAQ t-stat the controls the blower... But you will not get the red LED for 2nd stage.

I had the TH8320, and did that red LED, and liked it.. I upgraded myself to the new IAQ t-stat, and was willing to give up the red LED for a humidity control in A/C.

I'd put it back to the factory settings of 1 on first stage, and 2 on second.

With 3 that's a pretty far drop in temp before anything will happen. With the Honeywell VisionPro, you don't have that. the t-stat itself will decide if 2nd stage is needed..

[billva]

Are your gas rates and usage the same as 3 years ago? Have you added or replaced any other gas appliances?

Have you changed your filter?

[fortressofcomfort]

My guess is the thermostat isn't making THAT much difference in your gas usage.
I'd look elsewhere.

[tonyv]

Mayguy,

I have a VisionPRO TH8321 thermostat (with dehumidification control, but not the new IAQ). I installed it myself and didn't realize that I could run a jumper to indicate when the system is running on stage 2. How can I run this jumper cable to indicate when my furnace is operating at stage 2 heat?

Thanks,
Tony

[mayguy]

Mayguy,

I have a VisionPRO TH8321 thermostat (with dehumidification control, but not the new IAQ). I installed it myself and didn't realize that I could run a jumper to indicate when the system is running on stage 2. How can I run this jumper cable to indicate when my furnace is operating at stage 2 heat?

Thanks,
Tony

Do you know if you have a common wire hooked up? If you don't it won't work.

[tonyv]

Mayguy,

There is a common wire that was used with our previous Honeywell thermostat, but it doesn't work with the Honeywell VisionPRO.

We have a 2 stage furnace that is located in the basement, and a separate A/C system in the attic that was installed by the previous owners as they wanted the A/C vents on the ceiling (fine with me as this is the best setup). With the VisionPRO thermostat, the common wire must come from the A/C transformer. Ours comes from the furnace transformer. We tried using this common wire and it didn't work. Therefore, it doesn't appear that I will be able to install the jumper to indicate when the system is running on stage 2. :(

Tony

[mayguy]

Yeah, if the common wire comes from the A/C side, then the jumper will not work since it should be on the heating side.