Home Thermostat Wiring

[reemoe2]

I am attempting to install a programmable thermostat (Honeywell RTH7500d) to replace my old non-programmable Lennox 51M33), but have a question as to which wires go where on the new one.

The old unit uses wires O, R, G, Y1, W1, C, E, T2, and T1, with a jumper between W1 and E, as well.

The quick start guide of the new unit mentions O, G, Y, Y2, W, W2, R, Rc, and AUX, so am a little confused by some of the 'extra' wires that may or may not be needed.

Thanks in advance for any guidance!
Ryan

 

[DBMaster]

I have found that the help line - listed in the instruction manual is invaluable. There are a ridiculous number of minor differences in thermostat wiring configurations. The help line was useful to me in installation.

 

[Jim K]

I replaced mine just a couple months back and I labeled the wires before I took old one off and put them on the new one as they are marked on the new unit.Went real easy . The new is a 5-2 programmable Honeywell that replaced the old round Honeywell. I don`t program though I do it manual because of the odd hours I keep here at home no 2 days are the same.

 

[reemoe2]

On the doityourself.com forums, I was told it is not recommended to use a setback stat on a heatpump system (which mine is). If your temperature is more than 2-3 degrees below the set point.... the electric heat will come on, causing higher electric bills.

So my new Honeywell programmable stat looks to be beneficial during the cooling season (summer), but the opposite during the heating season. In my case, does anyone think I should potentially switch back and forth (current stat in winter / new programmable stat in summer) in order to save on energy usage? I was thinking a programmable was the way to go, but from what I've learned about how heat pumps work, I'm having doubts.

 

[reemoe2]

Hello again. I have finally found time to install my new Honeywell thermostat. Today, I had a question, so I called the Honeywell hotline phone number, and I was told that I need to have a HVAC contractor install a 'fossil fuel kit', otherwise the compressor may get damaged.

Is this correct? I'm really getting bummed, as I thought I was nearing the end of getting the new one installed myself.

I hadn't come across this during my research over the winter. We were talking about the T2 and T1 wires (Outdoor Temperature Sensor connections, per the old thermostat's manual). I was thinking that the T1 and T2 were simply not used with this new thermostat and could be taped off.

Thanks,
Ryan

 

[JayhawkRoy]

Install the new thermostat and leave it installed. You can change settings twice a year if you want different setbacks for summer vs winter. I run a 5 degree setback year round, and it seems to work well.

No knowledge of the fossil fuel kit at all.

 

[MCompact]

A fossil fuel(dual fuel) kit may be required if the heat pump's auxiliary/emergency heat is provided by oil, natural gas or propane. If you have electric auxiliary heat it's usually a non-issue.