Can I reuse heat pump thermostat in a conventional system?

[beltbuckle]

Last year I bought a nice Honeywell Chronotherm IV T8611G thermostat to replace our old mercury heat pump thermostat. I like this thermostat because it has adaptive recovery, and I can program every day seperately. (not like a 5+2 day).

Long story short, I will soon be replacing the heat pump and air handler with a new Trance furnace and A/C. I would like to keep my existing thermostat if possible because it is nicer than most of the ones the installers want to put in.

So my question is if a heat pump system can be used with a traditional furnace / A/C combo. My thinking was possibly the installer could just leave the aux heat and reversing valve disconneced, but I haven't put a whole lot of thought into this.

Anyway, if someone can provide any input I would sure appreciate it.

Beltbuckle

[git-r-dun]

Absolutely. Instead of "o" terminal use "W", should be available

[karsthuntr]

You may have to use the E term. if W1 is not on that stat.

I would ask installer about a Vision Pro t-stat. Much easier to program and you have the option for an outdoor thermometer.

[beltbuckle]

Great, thanks guys. A large problem is the sales guys they send out to do the bids don't have a great knowledge of everything. I recently go 5 bids for the new system, and I got the weird feeling that I knew more than 3 out of the 5 sales droids. The other two were also installers, so they knew what they were talking about.

[a\c don]

No.

Your heat pump thermostat energizes Y as 1st stage of heat.

Nuff said.;)

[git-r-dun]

Hey ac don are you sure about that? What tells the reversing valve to energize if Y is energized. Why would you use cooling for 1st stage of heating?

[karsthuntr]

If you don't have a W1 term than you would have to use E term and put t-stat on EM Heat instaed of just heat. I've done this a couple of times with cheap customers (not saying your cheap beltbuckle).

[a\c don]

Your heat pump is the first stage of heating which means the compressor starts and the reversing valve shifts using a heat pump t-stat.

Connected to a gas furnace and a straight cool condenser on a call for heat using a heat pump t-stat the condenser will start first, as the temp drops the furnace will come on as 2nd stage(w2).

Not a very pretty picture.

[a\c don]

Originally posted by karsthuntr
If you don't have a W1 term than you would have to use E term and put t-stat on EM Heat instaed of just heat. I've done this a couple of times with cheap customers (not saying your cheap beltbuckle).

On the cheap that would work since Em Heat locks out Y.

[beltbuckle]

So I take it this would not be a good idea then? I am not tryng to be cheap, I just happen to like this thermostat and if I can reuse it, I figured I might as well...

[git-r-dun]

I don't believe it's on the cheap. It poses no danger and will work fine for you. No it's not specificaly made for that, but bottom line it'll work. If you really like it you can go and get the T-8600 which is made for gas/electric heat

[Edited by git-r-dun on 03-01-2005 at 11:44 PM]

[beltbuckle]

I also forgot to mention that this model also has the optional outdoor temp sensor like the vision t-stat.

If it helps, I just found my manual for it. It has the following terminals:

C
Y1
G
O/B
E
W2
W1
R
X1
X2
L
OT (two of these for optional outdoor temp sensors)
OT

[beltbuckle]

And I might also add I am not the one that would be hooking this up. I was mainly wondering if it was reasonable/possible to ask the installed to reuse it.

[git-r-dun]

Get rid of the wire on O/B and hookit up to W1. That did help. Whether you hook it up or someone else does, it'll work

[Edited by git-r-dun on 03-02-2005 at 12:20 AM]

[stef]

Hey Beltbuckle,

The answere is NO and Yes.

NO - because the Y (compressor) terminal will be energized on BOTH heat call and Cool call.

Yes - Unless you do ONE of the following:

Option 1: hook up like you hook up for your heat pump without hooking up the O or the B terminal. Use the W1 as your first stage heat. THEN every time you want to run COOL MODE, you MUST change your system setting to COOL. IF YOU WANT TO RUN HEAT, then you MUST change your setting to EMERGENCY HEAT. Note that if you change your system to Gas heat then you will have cold air blowing out of your vent during the first few minutes before you get warm air because the FAN (G) terminal will be energized the same time as your heat.

But this option will limit you and you will also loose the AUTO mode on you system. If you leave the system to AUTO mode then your compressor will run on both HEAT and COOL modes. The AUTO mode is good when the weather if mild. In the morning the unit runs HEAT, then in the afternoon the unit runs COOL

Option 2: Use external relays to control your system, then you can still use it without any problem. It is not that difficult but require some logics. It is not that easy to tell and not having diagram to use for hooking up.

Hope that you can get someone to do it for you since I see that you really like your thermostat.

Have fun

[beltbuckle]

That makes sense stef, when I think about it. I think I will try to request a 8600 or vision pro, so my wife will not get confused with the "new" way it would be working.

[BaldLoonie]

On most newer Honeywell HP stats, there is a W1 and Y1 which are connected with a jumper. Some older White-Rodgers units were the same way. To use on straight cool, just remove that jumper and W1 energized the furnace with a call for heat. You would get the blower immediately because G would also be energized.

On many other stats, it isn't done this way and only solution was em heat. But what if you forget? One of our techs found this on a no heat yesterday. Running the A/C in 20 degree weather with a gas furnace blasting on the evap doesn't make for a happy compressor!

[stef]

Baldloonie,

You are right on some HW thermostat. But here he has a Chronotherm IV, which does not apply with your reasoning.