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We have an old mercury switch thermostat in our house, You know the type, gold ring, very common.

We are in new England on a gas/steam system. There is no central AC.

We have been told by more than one heating professional that there really aren't any decent alternatives. The problem is that the thermostat doesn't report the right temperature, so it basically functions as a switch. The other problem is that my wife hates it.

I think we are on a 2 rather than three wire system. The house was built in the late 1920's.

Does anyone have experience with alternative thermostats?

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Why do the professionals say there aren't any good alternatives? There are countless other thermostats on the market now. – BMitch Nov 4 '13 at 13:11
replacing mine like that for a moderately priced digital was the best thing I ever did. It seemed that for A/C, 60 degrees and 80 degrees were about 1 degree of rotation apart. :) Now I just need to get it recycled properly… It absolutely should not go into the trash. – Tim B Nov 4 '13 at 13:42
see Replace two-wire thermostat – mac Nov 4 '13 at 14:53

Almost every thermostat on the market today is a better alternative than a mercury switch-type.

Even the cheapest digital thermostats have schedules, so that they can have different heating points during the morning, daytime, evening and overnight, and range from having weekend vs weekday to 7-day indepedent schedules. This allows you to save money by turning down the temperature while you're not home or sleeping.

typical digital thermostat

On the more advanced side of things, there are internet-connected thermostats you can program/control from your PC/phone/etc, and ones that can self-learn based on manual adjustments and motion-sensing. There is a corresponding increase in price, and these typically do require a C-wire so since you only have two wires you'd have to pull a new wire for this.

NEST thermostat

To connect a basic digital thermostat to the 2-wires, the best thing is to follow the instructions that come with the thermostat. Typically you're going to connect the two wires between R (or Rh) and W.

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Agree that the modern thermostats are a huge improvement, but consider: a bi-metallic strip and a glass bulb with two electrodes and a drop of mercury. Functions for close to a century. No firmware upgrades, no Blue Screen of Death, no re-booting... – DJohnM Nov 4 '13 at 19:08

I agree with John (?) - simple, reliable, doesn't require batteries or power. Indeed, if you have gas you can have normal heat during power outages. If you are frustrated with the lack of temperature sensitivity, you might try messing with the bi - metallic strip and change its performance characteristics.

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For 30 years we had an old round mercury thermostat. It worked great. Then we bought a new Trane furnace with a new digital honeywell stat like the one above. The new stat freezes. It's programed and constantly gets stuck on the previous setting and doesn't adjust when it's supposed to unless I press a button, any button, then it wakes up and almost like it says "oh, sorry, I was sleeping" and corrects it's self. Im tempted to reinstall the mercury stat. And this isn't the 1st digital stat I've had problems with. It seems the digital stats I've encountered have a short lifespan, like smart phones. Perhaps they're designed not to last more than 2-3 years.

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Congradulations, you are the one millionth customer to complain about a honeywell thermostat. Don't bother asking, the HVAC guy checked and couldn't find any problem. – Ben Welborn Apr 6 at 21:06

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