Electronic thermostats

[Charlie R]

A couple of years ago I replaced my old home heating thermostat with an electronic one from Home Depot. It ran on a couple of AA batteries, had several programmable on/off cycles for the furnace and worked pretty good for a while till the touch screen quit. Got a replacement under warranty, slightly different model that required an entirely different mounting. The new one works fine, also powered by AA batteries.

Anyone considering these needs to know that there's no backup for the batteries. When they die the house gets cold. The new thermostat eats (cheap) batteries in about a month. The original thermostat, with a mercury contact, lasted forever and wasn't battery powered. When I get time I'll run more wires between the thermostat and the furnace to bring power to the thermostat in addition to the batteries, which is a nice feature of this thermostat.

The thread on testing batteries reminded me I wanted to post this before the heating season begins.

[sweensdv]

Do you put new batteries in that thing whenever you go away for more than a day? I'd be a nervous wreck the whole time I'd be away if I had to depend on batteries to run my thermostat. As cold as it gets around here in the winter a house could freeze up and burst pipes in no time at all if the batteries died while I was away.

[trungdok]

Do you put new batteries in that thing whenever you go away for more than a day? I'd be a nervous wreck the whole time I'd be away if I had to depend on batteries to run my thermostat. As cold as it gets around here in the winter a house could freeze up and burst pipes in no time at all if the batteries died while I was away.

When you leave the house for an extended amount of time, wouldn't you shut off the water, open a few faucets to relieve the pressure, and shut off the heat? As far as I understand, pipe bursts happen when the water freezes, thus expands in volume and create pressure in the pipe. That pressure is what bursts the pipe. If you open the faucet, then you can relieve that pressure.

[phrog]

Charlie, I had one of these put in my house two or three years ago. The guy who put it in ran another wire so that batteries are solely for backup on mine. The only time the batteries come into play is if the electricity goes off, the batteries hold the settings. (The furnace will not work when the electricity is off because of the electric blower.) I just recently replaced the batteries for the first time. (There is a little icon shows up when the batteries need to be replaced.) Yours will probably last longer also when they are taken off "active duty."

FWIW, this thermostat holds a much more consistent temp than did the old mechanical thermostat.

[capncarl]

I suppose if you did not have an alternate power source such as the furnace transformer you could provide a large lanter battery for the back up. Any way you look at it though, if the power went off while you were away the furnace would not work either.

[sweensdv]

When you leave the house for an extended amount of time, wouldn't you shut off the water, open a few faucets to relieve the pressure, and shut off the heat? As far as I understand, pipe bursts happen when the water freezes, thus expands in volume and create pressure in the pipe. That pressure is what bursts the pipe. If you open the faucet, then you can relieve that pressure.

If I were going to be away for just a few days I wouldn't do all the things you mentioned. I probably would do most of the things on your list, and a few more, if I were going away for an extended amount of time but one thing I would never do, if it were winter time, would be to shut off the heat! Lowering the temperature setting would be the best way to deal with that.

My point was that in some parts of the country where it gets extremely cold in the winter a thermostat that depends solely on batteries to power it is probably not the best choice.

[gerti]

Great opportunity to put in a NEST:

http://www.nest.com

[Pappy]

Great opportunity to put in a NEST:

http://www.nest.com

At $249 it pays for itself in a year and a half, if your savings match their estimates. (Just like getting the 36 MPG city that new car advertised....)

[LCHIEN]

unless you're away on a schedule that the Nest can learn, it seems like the savings might be minimal. For example my wife is stay at home, she's home most days and always turns the thermostat up (AC) when she's out. I don't really think the Next can help me much, except maybe to adjust the temperature from my easy chair.
Furthermore my wife runs hot and cold so she's always turning the tmperature up and down.

BTW, steadier temperatures are not necessarily good. AC's and heat basically run full blast or not. So the temperature ramps (for A/C) up when its off and down when its on.
If you try and keep the temperature too constant the A/C will cycle on and off more often which is both inefficient and hard on teh machinery stopping and starting. Most thermostats have something like a 2 degree hysteresis (difference in top and bottom temperature of the up-down ramp) which limits the cycling rate of the A/C and still keeps it close enough for comfort.

[gerti]

BTW, steadier temperatures are not necessarily good. AC's and heat basically run full blast or not. So the temperature ramps (for A/C) up when its off and down when its on.

Modern HVAC systems have more than one stage and can modulate both heat and cool at high efficiency. They tend to come with proprietary controllers though (like Carrier).

[LCHIEN]

Modern HVAC systems have more than one stage and can modulate both heat and cool at high efficiency. They tend to come with proprietary controllers though (like Carrier).

I don't think those multistage units are but a small part of the market. Most people don't have them. I don't. And you're right, the Nest can't control them. So my point remains there's only a little wiggle room for finer control of temps with the Nest or similar smart thermostat.

[iceman61]

I think the basic rule of thumb now is to change the batteries when you have to run the clocks up or back. That being said, I never follow that schedule. My schedule on battery change out is far more that that.

[JimD]

I have a newer furnace with a two stage blower for the first floor and basement and an older heat pump with a thermostat like you describe for the second floor. I don't replace batteries more than once a year, however. I like the thermostat with the newer furnace but I have to admit resorting to the booklet sometimes when setting it. It has a vacation setting in addition to heating and cooling schedules. I can't set it over the internet but I'm not sure I want to. Anybody else notice the article about hackers going after cars and home controllers? I'm not sure what they would do with my furnace controller but still if it is not on the internet it is not at risk.

Jim

[Woodshark]

Something is wrong. I went with digital thermostats over ten years ago. My AA batteries last for years. I think I have to change them maybe every three years to four years or so. Try better batteries or another thermostat. Mine are Honeywell.

[LCHIEN]

It would seem to me that a digital learning thermostat, even one with wifi and internet built in, could run off a few milliwatts of power essentially skimmed off of the control voltage for the relay. Batteries then would only serve as backup devices for the settings and memory when the AC power failed and in that case would not even have to run the display or control function - just have to hold the settings and maybe run the time of day clock.

So it would seem that battery life of less than a year is kind of short. Alkaline batteries should have a lifetime in such an application essentially equal to the shelf life of the batteries, which should be several years.