Hi. I was wondering if it is possible to install the digital thermostats with the older wiring in my home....the thermostat I have now (a round dial type--Honeywell) is only connected to a2 black wires. There are no other wires coming up thru the wall that I can see. My furnace is older (about 15+ years) and I do not have air conditioning. I am having a very difficult time regulating the temp even with a newer "old style" thermostat and REALLY want to use a digital, but can't afford new wiring at the moment. If I can't do a digital, any recommendations on how I can get this to be a tad more accurate, I would greatly appreciate it!!

Thanks!
Kym

omzig

Yes most of them will work with a 24v 2-wire system. You won't be able to control the fan independently with two wires but otherwise it will work. On most of them you will connect your wires to the terminals marked "W" and "Rh", but refer to the manual.

Be careful not to let the wires fall into the wall when you remove the old thermostat.

kdean823

Does it matter which black wire connects to which? The thermostat I bought a couple years ago didn't specify any of this in the user's manual as far as what to do if you didn't have all the colored wires. I don't know if a newer one would, since I'd pretty much given up on the idea until I found this board.

Thanks!
Kym

labman

I agree there are many digital and programmable thermostats that will work on a 2 wire system. Just look for one with the voltage stealing feature that grounds through W terminal. You may or may not need to sort out the wires and get the one directly from the transformer connected to the RH. The bit about not losing the wires was good too.

I am not sure a programmable thermostat is going to solve your problem. Perhaps you need to explain it better. If the thermostat is allowing too wide of swings in the temperature, and a new conventional one didn't solve the problem, an expensive programmable one may not either. If the thermostat you have now still has a mercury tilt switch, realigning it so it is level might help. If it is poorly placed, no new one will help. The thermostat should be on an interior wall away from drafts, fireplaces, and anything else to give false high or low readings. Rerouting wires to a new location isn't a big job if you have the furnace in an unfinished basement. I can help explain how if you ask.

NorthernHeat

Any digital stat that runs on batteries will work. Just connect Rh and W, it won't matter what black wire goes where. Labman pointed out alot of important things to know about the location. Merury buld thermostats like Honeywells T-87 must be level when installed of they won't be very well calibrated.

kdean823

Well, it's got the mercury, so it could be a leveling problem. The thermostat is in the hallway by the bedrooms....follows all the "rules". The problem I have is that when I set the thermostat for 68, it may be 64 according to the temp gauge. I can have it set at 70 and we will be freezing. Other times, it seems like a slight adjustment in temp makes it very warm in here! With the gas prices, I just want to keep it at an accurate temp so I can try to save money instead of constantly adjusting up and down!

Thanks for all the help! I'm going to take a look at the one I bought and see what I can figure out now from the instructions.

Kym

kdean823

Ok, I've finished installing the new one. So far all seems well. I guess we'll see when it comes down to keeping it at the right temp. Currently it's warmer in here than I have it programmed for, so keeping my fingers crossed. One thing was that instead of just a "W" wire spot, there was a "W1" and "W2" I assumed that W1 was correct for me, so if I'm wrong, someone holler!! I'm excited that I might actually be able to keep a steady temp in here!!

Thanks! I'm sure glad I found this board!
Kym

NorthernHeat

W1 is correct