HOME AC*HEAT Thermostat Replacement HELP??


What I have is a system which is called a "heat pump" but it does have both heating and air conditioning and it's sometimes called a "central unit". It has one of those very old mercury switch type thermostats that adjusts the changing temp by using some old coil-spring like system and is controlled by sliding the temp knob left or right.
With this type of system [heat & AC] can I replace this thermostat with a Digital Thermostat?
I've Googled this and cannot come to a good comparison chart or report on the various Digital Thermostat Replacement products, could you help me find such a website?
Is replacing the OLD Thermostat with the NEW Digital Thermostat something I can do myself? I've done simple things like replacing ac outlets and ac light switches many times so would this be something I could also do myself?
Oh yeah almost forgot, What is a good price for a Digital Thermostat for a home AC and Heat system?
And what kind of saving$ would I see by this replacement? I live in the southeast so we use the AC about 9 months per year.
Let me know if I didn't make something clear, I'll try to.
Thanks
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OMG I forgot to add that the 'current thermostat' has controls to access the following features with my system. 1 heat 2 emergency heat 3 ac 4 fan
thanks
sayd the following:

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If in fact it is a heatpump, you need a heat pump thermostat. Those have an extra wire for the change over valve circuit, orange I believe. I bought one over the internet, for around $70. You want a programmable one, so you can set it back when you don't need heat or cool, that is where the real savings comes from. Auto changeover is a nice feature, as you don't have to slide a switch to go from heat to cool. I just looked at Ebay & found lots of them.
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Last year I replaced an old mercury and spring based thermostat with a Hunter Auto Temp Heat Pump Model 44760 picked up at Lowe's.
Best money I ever spent. I had to hire an HVAC guy to bring an additional wire needed for the new thermostat, but even so has paid for itself in a few months. I am in South Texas.
It's programmable, so I can set 4 daily time slots and decide what temperature I want for each one. Every day of the week can be programmed individually, if needed . When reaching the threshold temperature I set it will switch between heat and cold automatically.
Go for it. Of course Hunter is not the only game in town, but whatever you choose or find, make sure to have many programming options and auto switch cold-heat.
Robert Blass wrote:

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This house has people in it 24 hours a day so I wouldn't need to program it, but would it still help the power bills?
Also, I have special things like emergency heat and a fan setting, is that a DIY with a new digital thermostat or would I need an electrician?
thanks
following:

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The energy savings you get with thermostats comes almost exclusively from them being programmable. That allows them to automatically change the set temp for different periods of the day. For example, setting the temp down to 62 at night during the winter, versus leaving it at 70. Changing from an analog thermostat to a digital one and not using the programmable setback is not going to make a substantial difference in energy usage. You could get some benefit by the new thermostat doing more efficient cycling, but any such benefit is going to be small compared to the setback amount.
I like the Honeywell Vison Pro thermostats, but if you aren't going to use the programmable features, it's overkill.

As long as the existing thermostat has those features, you can get a compatible replacement digital one that a reasonably skilled person can hook up.
The real question comes down to what you're trying to do. If it's to save energy, I doubt changing from what you have to a digital one is going to make any significant or worthwhile difference, unless you use the setback features.

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Do those people sleep at night? You could still lower the setting for those hours.
As I said, I installed the thermostat myself, but had to hire help to bring a new wire to the unit. More than an electrician, you need someone who knows HVAC.
Robert Blass wrote:

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This time of year, I find it necessary to change the A/C setpoint at night. If I don't it gets much too cold.
[snip]
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Mark Lloyd
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wrote:

Only if you can live with it cooler at night. A good heatpump thermostat can do that and bring the temp back up without firing the emergency heat and losing you money. If you never want the temperature to change, there is absolutely no point in replacing the thermostat.
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Robert Blass wrote:

The extra wiring may have been a common wire to operate the digital thermostat. One thing you could do is check with the manufacture of the existing stat and see if they have an upgrade. Emergency heat setting is when the heat pump doesn't work so this way you will have some sort of back up heat like electric strip heaters.
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That IF NEEDED is important. It you don't need those different periods, do you have 28 times as much work to do when you want to change the settings?

That's a useful feature sometimes. Reading about it here, has encouraged to get mine working that way.

I consider it important that the design makes it easy to do simple things. That's not always true with an electronic thermostat.
[snip]
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Mark Lloyd
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wrote:

Could you open your current thermostat and tell us what colors the wires are coming in; what the terminals they go to are labeled, or if nothing else - how many wires there are. The nomenclature information (who made it, what the model number is,) would also be helpful
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