My old house has a 3-wire thermostat, and I can either use a mechanical thermostat, or one that uses AA batteries.
I want to put in a smarter thermostat that requires power supplied by the furnace. This requires more wires. I'm thinking of pulling out the old wire and put in new thermostat wire. I think the maximum I can get is 8-wire. Is it advisable to do this or is 5-wire sufficient? The 8-wire will be harder to pull/fish.
What kind of furnace uses 8-wires anyway?
Hi, You'll have spare wires then. If you don't use a/c, 4 wire is needed. Or forget the wire all together and go wireless. I did that and we can move thermostat to any spot in the house.
hermostat, or one that uses AA batteries. I want to put in a smarter thermo stat that requires power supplied by the furnace. This requires more wires. I'm thinking of pulling out the old wire and put in new thermostat wire. I think the maximum I can get is 8-wire. Is it advisable to do this or is 5- wire sufficient? The 8-wire will be harder to pull/fish. What kind of furna ce uses 8-wires anyway?
5-wire should be ok, but I like the wireless idea even better.
Wireless may be fine for now, but if you switch to a high end system like Carrier's top-of-the-line Infinity, you have to use their wired thermostat that goes with the system.
The communication between units is computerized. It does not use a lot of wires. Five will be enough. Shielded could be a bonus in an electrically noisy environment.
Don.
Another option is just get one of the thermostats that will operate off of batteries and change them once a year. Most of the programmable ones work like that. I have a Honeywell VisionPro, which is a really nice one that I recommend. It will work with either battery or furnace power. The advantage to furnace power is:
1 - You can set it so the display is backlight all the time. With battery it only lights when you touch it to use it. 2 - You don't have to worry about changing batteries, or having dead batteries in winter when you're not there, etc. Some thermostats have a backup mechanical that closes at 40F or so to prevent freezing.This requires more wires. I'm thinking of pulling out the old wire
Typical is:
heat cool fan common
That's 4.
Add in your additional power wire for the thermostat, and you're at 5.
next level of complexity is two stage heat and/or cool which would add one more wire for each stage. So two stage heat, two stage cool, which is common, would be 7 wires.
Then some thermostats can control a humidifier, which I presume adds an additional wire. That would give you
If you're re-wiring, I don't see pulling 8 wire being much different than 5, either in cost or difficulty.
Regular heat pump systems. The thermostat cable installed for a heat pump may actually have 9 wires in the sheath. Me and GB always ran a cable containing more wires than immediately needed. There are adapters available for multiplexing a few thermostat wires into more connections for updated thermostats. The cost of the adapters is cheaper than the cost of labor needed to run a new cable. ^_^
TDD
Hi, That's what I got Carrier IAQ system. (Infinity) I made it work. When they installed the system, control part, I did.
If me, I'd go for the 8 wire and buy more thermostats from Braeburn. They were as easy to work with as if they were the corner hardware store!
Can you use the existing wire to pull the new wire? I couldn't some idiot stapled the old wire to the studs!
Well, that's what you're supposed to do in new construction; in retrofit work you are allowed to not staple it if you aren't opening up the wall... but if you have access to the underside of the floor from the basement usually you can just drill a hole through the plate, or use the old one, and drop the wire from the hole behind the thermostat with only a little fiddling around.
Once I got very very lucky and a sharp jerk on a piece of Romex was able to pop the staples out of the studs enough that I could pull it out and a new piece in behind it (was replacing an ancient 14/2 with a new
14/2WG and replacing one run in an existing wall was all that was required to properly ground a whole mess of work.) Didn't hurt that the new Romex was physically smaller than the old cloth covered stuff; that won't be true when replacing a 3-conductor thermostat wire with a 5 or 8-conductor one.nate
I've had good luck with them myself. Only complaint being the latest one I purchased - which appeared to be the updated version of the same on that I had in my last house - only runs off batteries, the directions tell you not to connect the 24VAC wire from the furnace controller. Now it's been in use for several months now with no apparent issues and no battery changes, but just on principle I would prefer that the batteries be for backup only as they were on my old thermostat. Also reprogramming after a battery change is a pain in the keister (it's a
5/2 programmable deal, part of the reason I got it. The other being that it has an "Auto" mode for the few times a year that you may need to switch from heating to cooling or vice versa in the same day.)All in all, if I'd known that it didn't take the 24VAC input, I'd have purchased a different model. (ordered it online as it was $20-something vs. $60-something locally.)
nate
Lithium batteries last ~3 times longer.
Some Vision Pro comes with RTA(return air) sensor. Drill one hole into return air plenum to mount it. One wire from it to thermostat to use this fall back freeze prevention feature.
Being a Honeywell retiree, I am always for Honeywell 'stats.
Hi, If you must, there maybe a unused battery compartment in that 'stat. Jury rig to put in rechargeable batteries in there and build a small charger/regulator on a breadboard and hang it behind 'stat and drive it with 24V AC coming from the furnace. I'll be 73 next month. My brain still works pretty good but little slow. Always looking for some thing to do or I still play my euphonium driving family crazy(just better half now), LOL! I never used 5-2 programmable one.
That would actually be a great idea, if I didn't have 20 more important projects to do as well. That's how I would ideally like to have the thing work, have the power actually charge up rechargeable cells which kick in only when AC power goes out for a true zero-maintenance (until the cells actually die 10 years or so down the road) system.
I'm assuming you could just maintain a constant voltage on the cells, that way you could piggyback right on the terminals of the cells and make a crappy little power supply to keep them trickle charged. It wouldn't actually power them up if they were run down, or at least not quickly, but it'd be cheap 'n' sleazy.
nate
Putting the new thermostat you don't like up on Ebay and getting one that runs off system power sounds like a much easier and simpler idea.
Nate Nagel wr
Hi, There are all kinda ASIC for the purpose, it is not that hard to do. I have two weather stations, one at home(Davis, which is good stuff), one out at cabin El Cheapo Chinese knock off with 2 AA cells. I converted this one to rechargeable Ni-Cads and used a piece of solar cell from garden light to charge them. It is going into 3rd winter now since, no trouble at all. Davis one is on solar charger as it came which is connected to NOAA grid on the 'net.
That's good to know. I'll avoid Carrier like the plague.
A shield is superfluous. Five may not be enough, depending on the system. I believe mine has 8 (not all are used, currently).
If I'm designing the HVAC unit and thermostat, sure. If I'm buying one off the shelf (infinitely more likely), not so much.
Hi, If number of wire is not enough you can use multiplexer(s) which make one wire acts like two for an example. Different signals time sharing one wire. Advantage of digital circuitry.
The battery may be connected to the thermostat wires through the thermostat circuitry (not isolated by relay). Charging off of the 24VAC may not be as easy as it sounds.
There used to be thermostats with rechargeable batteries that charged with the voltage across the open stat contacts.
There are definite advantages to a high end Cariier system. Like variable speed and precise humidity control.
Don.
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