After moving into a new apartment, I am really missing having a programmable thermostat. Unfortunately, there is no power to the current electromechanical thermostat, so I can’t just replace it with the spare one from my house (I think), so I’m looking at battery-powered programmable thermostats.
Has anyone had good experiences with a particular model/brand? I would prefer a 5day/2day thermostat, both heating and cooling, and I’m not worried about freezing pipes (Texas apartment) if the battery runs out occasionally.
Alternately, will my old Honeywell Chronotherm III work reasonably off of its battery backup with no wall power?
About 90% of residential thermostats are Honeywell; you can get $10 mechanicals to pricey wifi programmables. I’ve had good luck with them, and I am pretty sure all the ones I’ve ever used are battery-powered. My current house has one AC thermostat, which does have 24VAC power, and three heating thermostats, which don’t. I replaced the AC and one heating zone with a fairly fancy touch-screen model, and the two others with simple battery-powered programmables.
Home Depot and others have the range of programmables from single-setting to 5-2 to 5-1-1 to 7 days - shop around and spend what you like to get what you want. Put good, name-brand batteries in it (usually AA) and you should get two years or more of service.
The Nest can use, but does not require a (usually blue) C wire for power. ISTR that it charges its internal batteries while the air or heat is running if there’s no C wire.
My Honeywell Wifi stat does require power from a C wire, but there is a workaround to “steal” the green G wire (used to turn the fan on). You won’t be able to manually turn the fan on, but it will still go on and off automatically with the furnace/air conditioner.
All you need to do is disconnect the G/green wire from the G terminal at the air handler and move it to C, and do likewise at the thermostat. If you want to retain all functions, there are some electronic things that let one wire behave as two.
ETA: Forgot to say that in my case, on careful examination, I found the blue wire had been clipped off at the thermostat end, so all I needed to do was peel back the cable jacket and connect the wire.
Nest, IMVHO, is phenomenally overrated and overpriced, a marketing campaign for a collection of old and largely disproven or phantom notions. (The very best implementation of programmable thermostats saves somewhere below 20% in most households, and less in many. Making the controller uber-intelligent and glitzy doesn’t change this. It’s the 200MPG carburetor for houses.)
The OP is looking for a cheap solution for an apartment, and a 1-week programmable will likely get him 95% of the energy savings any more sophisticated (make that “sophisticated”) solutions will provide.
There aren’t many cases where external power is needed, as long as the control loop includes a transformer at some point. Systems where the “thermostat” is the source of the power for solenoids, valves, circuitry etc. are pretty rare, IME, and mostly confined to things like wall heaters.
AC power for a nominally battery powered thermostat might be a “safe” option in harsh climates and industrial settings, but really, a pair of AAs, while small on a stripper, are plenty big to power a household thermostat for quite a while.
The fairly cheap one I have has a battery level indicator on the front panel if you really care. I’d say the ease of doing temporary temperature adjustments and how you like the display are the biggest things to look for. (As well as 5 day - 2 day which are standard.) They shouldn’t be rocket science. I found that the hardware store brand was a bit cheaper than Honeywell, but I mostly chose it based on these features.
However I live in the Bay Area where it seldom gets too hot or too cold, and we don’t have AC, so the thing is shut down 9 months of the year, often.
I like being able to track the usage (we have a heat pump, and electricity ain’t cheap)
I like being able to remotely access the units (we have 2 houses in different states) and tweak the temp if we’re heading to a hot/cold house that’s been empty for a while, or being able to up the temp in the poorly insulated TN house if there’s a sudden cold snap that threatens to freeze pipes.
I like the auto-away feature that turns the unit up/down (depending on season) if it determines the house is empty for more than 2? hrs.
I like the energy saving settings on how the heat and AC run.
Ah hah! I couldn’t check until I got back, but it turns out I also have a blue wire that had been cut shorter and folded back into the wall. This leaves me with red, green, yellow, white, and blue wires.
My old thermostat has connectors for O,W,G,C,R,B,Y. It also notes on the back, “C terminal must be connected to common side of system transformer for device to operate.” My first inclination was to wire White to W, Green to G, Red to R, Blue to B, and Yellow to Y, but that leaves nothing for C. Do I need to run blue to C? It doesn’t look like the O or B terminals were used in the last installation.
So I tried running blue to C instead of B, and while the fan turns on correctly, the AC doesn’t seem to turn on. Perhaps I need to jumper something? I’m going back to the dumb thermostat until I figure this out.