Questions tagged [thermostat]

Mechanical or electrical device used to control a heating, ventilation, and air conditioning (HVAC) system, or other temperature reliant system.

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93
votes
7answers
509k views

How can I add a “C” wire to my thermostat?

So, the spiffy new wi-fi thermostats want power on the C wire from thermostat, but the old thermostat doesn't have a C wire at it. What's the easiest way to add the C wire/24 volt to the thermostat ...
19
votes
1answer
157k views

How do you trigger the HVAC with wiring only?

I have a HVAC that has the usually wiring C R G W Y Pinouts What wires do I need to connect to turn on Heating? What wires do I need to connect to turn on the A/C? Is there a risk of damaging any ...
18
votes
4answers
67k views

Why don't programmable thermostats automatically switch between “Cool” and “Heat”?

While I can set my house to be a particular temperature, I still have to manually switch it between "Heat" and "Cool" mode, and this seems to be true of every thermostat (programmable or not) that I'...
17
votes
2answers
6k views

Do I need to be legally qualified to install a Hive smart thermostat?

As a competent DIY'er, am I legally allowed to install Hive myself? The reason for the question is I have been asked to provide a cert as I'm selling the house. If not, can someone point me in the ...
12
votes
5answers
76k views

Why is my Nest thermostat not working with A/C?

I installed Nest thermostat a few weeks ago, replacing an old Lux programmable thermostat (there was nothing wrong with it). I connected 4 wires (R,W,Y and G) to the Nest. But as soon as I'd ...
11
votes
5answers
2k views

Most cost effective thermostat setting: consistent temperature vs. lowest temperature possible

The problem: Our heating bills are about 25% higher than our average neighbors according to our bill, yet our temperature is always as low as we can stand it (mid 50's), we have excellent insulation ...
7
votes
4answers
3k views

Buying a programmable thermostat to replace a manual one: any considerations?

I'm about to look for a programmable thermostat to replace a manual one. There are already a couple of good questions on thermostat replacement that make the task seem pretty straightforward for ...
6
votes
3answers
4k views

Apartment building's thermostat located in unheated common area is cooking the tenants

In my apartment building, we have a steam heat system with radiators in each of the six apartments. The thermostat is located in the stairway/common area, where there is no radiator or exposed heat ...
6
votes
2answers
2k views

Reviews on Nest Thermostat - That Learns [closed]

I am just wondering if anyone has used Nest | The Learning Thermostat. At $200 it is very expensive, and I wanted to know if it is worth the price!? Is it practicle, is it actually smart? How precise ...
6
votes
2answers
21k views

Replace two-wire thermostat

I'm replacing an old mercury thermostat with a digital one. The new unit has 7-8 connections (labeled w1,wh,r1,rh,y,c, etc.) and a bunch of instructions about how to connect similarly labeled ...
6
votes
7answers
107k views

Should I use 12/2 or 12/3 to wire a 220V electric baseboard heater and thermostat?

When I bought my baseboard heaters, thermostats and 220V breakers I was advised to get 12/3 wire. When I attempted to install the heaters I found that the thermostats, heaters, and even breakers have ...
5
votes
5answers
29k views

Would the “Nest” thermostat work outside US?

Looking at this Nest question reminded me that I'd really want one of these for my future house. The Nest website says that it's currently only available in the US but I'm wondering whether that is ...
5
votes
4answers
11k views

Risk from installing a “Nest” thermometer without shutting off home power?

I'm trying to install a new Nest-brand thermometer in my parents' house (unscrewing a thermometer from the wall and screwing on the new one. The first instruction in the manual is to shut off power ...
5
votes
2answers
326 views

How to hardwire combined HVAC system for cooling?

I had to borrow the Nest thermostat from one of my units for another one where it was more needed, while a replacement is on the way. The unit from which I borrowed is combined HVAC (heat+cool) with ...
5
votes
2answers
54k views

Controlling separate heat and AC devices from a single thermostat

I have hydronic radiator heat powered by a gas furnace situated in one mechanical room of my house and a currently being installed central AC whose air handler is situated in another mechanical room (...
5
votes
1answer
190 views

Does lack of zone control delay hurt heat pump?

I had a new HVAC single heat-pump system installed with dual zone controls: 2 thermostats and 2 dampers for separate zones. The system works, but the zone control board does not have any time ...
5
votes
1answer
3k views

Is there a wireless thermostat that will make relocating easier?

I've got a single zone which covers all three upstairs bedrooms in my home and the thermostat is located in the master bedroom. We prefer it to be somewhat cooler at night, but the baby in the ...
5
votes
2answers
434 views

Is it Code to support Class 2 (thermostat) wires using a gas line?

Related to this question. Our gas furnace, while quite functional, has some quirks in its installation. One of them is that the installers cut off the old (original to the house) thermostat wires at ...
5
votes
2answers
3k views

Why is my indoor A/C Blower randomly turning on and off only with Nest?

I recently purchased a Nest Thermostat (3rd Generation). My old thermostat was working perfectly. I wired Nest the Same exact wiring as the old thermostat which is : Y1 W1 G RH RC. With Nest, the ...
5
votes
2answers
3k views

Line voltage thermostat to shut off attic fan when outside temp is close to inside?

I have an attic fan with a thermostat, but with the high heat these past weeks, the outdoor temperature is often above the thermostat setting. Thus, I'm just replacing all the air in the attic with ...
5
votes
1answer
216 views

Adding a C wire to older 3 wire

How do I use the green wire as a C wire as suggested in most installation instructions for the newer wi-fi thermostats? They all reference terminal strips at the furnace, all I have is the 3 wire ...
4
votes
5answers
155k views

Why does my pilot light keep going out?

My furnace pilot light keeps going out so I changed the thermocouple. Now the furnace will come on and heat up to the degree set on my thermostat, then the pilot light will go out and the furnace will ...
4
votes
3answers
110k views

How to wire multiple thermostats

I would like to have two thermostats controlling a single furnace. However I'm not 100% sure how I would need to wire everything to achieve the correct effect. Assuming a thermostat simply acts like ...
4
votes
1answer
9k views

Convert line voltage heating system to use low voltage thermostats

I currently have two line voltage ceiling radiant heating systems in my condo each with their own DPST thermostat. I'd like to use low voltage thermostats such as the nest. I found this transformer/...
4
votes
4answers
15k views

What would cause a clothes dryers thermal cutoff to keep tripping?

I have Kenmore dryer model 110.96588210. For about 10 years it worked flawlessly. Then, its thermal cutoff started blowing in an unreasonable frequency. Since the hi-limit thermostat must be replaced ...
4
votes
2answers
2k views

How do I make a 110V fan turn on when the thermostat turns the AC on?

I have installed a new a/c with thermostat...easy enough, but thought to add a fan to the mix. Basically, I'd like to add a fan to increase ventilation into a second room that would turn on whenever ...
4
votes
3answers
12k views

Is voltage too high in C wire going to thermostat?

I've managed to add a C wire to my thermostat. I then decided to check the voltage between the R and C wires, and find that it read as 27.8 volts, not the 24 volts it was supposed to be. Could this ...
4
votes
2answers
3k views

How can I connect a WIFI thermostat to a Honeywell R845A switching relay?

I'm trying to install a wifi thermostat and it won't power up. The old thermo was battery operated 2 wire but there were spare wires. At the R845A relay, red and white whites connect to terminals 5 ...
4
votes
2answers
13k views

Should my thermostat's blue wire be going to W2?

I've recently moved into my first house and am looking to replace the existing basic thermostat in the home. Here is a picture of how I found it wired: Researching the wires, I've read that commonly ...
4
votes
2answers
10k views

How should I install a thermostat for a baseboard heater?

How would I go about installing a thermostat for my bedroom's baseboard heater? I've seen lots of articles on how to replace an old thermostat but I'm installing a thermostat for the first time here. ...
4
votes
4answers
4k views

Connection for C wire on Mastertrol Mark V zone control panel

I have spent hours searching the web for information on this 20+ year old zone control panel, which supports 3 zones of Heat and A/C. The thermostat I'm replacing (on Zone 3) connects to T4/T5/T6 as ...
4
votes
5answers
4k views

Is there a through-the-wall A/C that works with external thermostats?

Our two-story A-frame house only has duct-work downstairs in the crawl-space, with vents in the floor. It gets quite hot upstairs during the summer, but because the square footage of the upper floor ...
4
votes
1answer
257 views

What could cause my boiler to provide hot water, but not heating?

My boiler kicks in when the thermostat asks it to, but when my room thermostat asks the boiler to fire up, nothing happens. My room thermostat clicks on, and lights up so I think it can tell the ...
4
votes
2answers
39k views

Workarounds for single-zone HVAC? Second thermostat? Adjust vents?

I have a two story brick home built in 1970 with a relatively new HVAC system blowing through original ductwork. In the summer its too hot upstairs and too cold downstairs. I know that the full ...
4
votes
1answer
180 views

Is it possible - setting thermostat based on a separate thermometer

I'm looking into building a solar water heater, but I'm wondering, is it possible (and what products should I be looking for) to turn on a pump when the water in the solar heating device is hotter ...
4
votes
1answer
2k views

What's wrong with my thermostat (fan / limit control)?

I previously asked about wiring the White-Rodgers fan/limit control on my wood stove. It's now wired and the wood stove is fired up. I ran the fan wires to the fan (hot) and I capped the limit wires....
4
votes
2answers
13k views

Can I use the T terminal in my furnace as the C for a Wifi Thermostat?

I've read many posts on this, and believe I know what to do, but want to make sure. My furnace (a Lennox G14 Series) does not have a C terminal which needs to be connected to the C terminal in my new ...
4
votes
2answers
23k views

Where do I connect my C wire from my thermostat when there are two transformers?

I have a Laars gas boiler that has 3 heating zones. I want to replace the old mercury honeywell tstat on the 1st floor (heat only) with a newer honeywell RTH9580 wifi model. I've taken pictures of my ...
4
votes
1answer
1k views

How can I determine if my HVAC system has features which are not currently wired to my thermostat?

I recently upgraded to a Nest Thermostat. This new thermostat supports many more terminals and features than my previous thermostat. My old thermostat had the basic terminals; G,R,C,Y, and W. I am ...
4
votes
3answers
31k views

Are there any ductless mini split systems that offer standard HVAC wiring controls?

Have been looking for in the US a ductless mini split heat pump system something like the Mitsubishi Electric Mr. Slim that uses a non proprietary wiring scheme for its wall mounted thermostats. ...
4
votes
1answer
16k views

How should I wire this White-Rodgers fan and limit control? What about the thermostat?

I have a wood-burning stove, that is used as an auxiliary heat source in the house. There's a regular electric furnace, and adjacent to it is the stove. The warm air duct (out) from the stove ...
4
votes
3answers
13k views

How can I wire my WIFI thermostat to control my millivolt fireplace?

I have a gas fireplace that has an millivolt on/off switch on my wall (and a remote that includes flame on/off, a countdown timer and a thermostatic flame control). I want to be able to program ...
4
votes
1answer
95k views

On a thermostat, are “R” and “Rh” terminals the same thing?

I have an older thermostat controlling an old ass Trane furnace with A/C. It has an "R" terminal and an "Rc" terminal (they are jumpered - see photo). I see references to an "Rh" terminal online. Are ...
4
votes
5answers
44k views

Adding a C wire to a new Honeywell WIfi Thermostat

I am trying to install a new Honeywell touchscreen WIFI thermostat and need to add a C wire to my terminal inside the furnace (using the help found at How can I add a "C" wire to my ...
4
votes
2answers
833 views

Why won't my thermostat control the HVAC anymore after trying to switch thermostats?

I bought a new Nest thermostat which is supposed to be compatible but needs a professional installation (advice that should have been heeded by non-professional electrician me). This is to replace an ...
4
votes
9answers
261k views

Why won't my A/C turn on after I replaced the thermostat batteries?

Our thermostat died yesterday, but after replacing the dead batteries with fresh batteries, and confirming the LCD screen was operable, our AC no longer turns on. I have attempted a factory reset on ...
3
votes
3answers
920 views

How many wires should be in a new thermostat cable?

When roughing in thermostat wire, how many pair wire would you use to cover most thermostats? I'm asking because keep seeing questions about C wire and wifi.
3
votes
4answers
28k views

Why won't my AC system turn off after I flipped the breaker?

We've got a central cooling air conditioner that was installed in 1984 with a thermostat from that same year. We are replacing the thermostat with a new programmable one (which has a 100% ...
3
votes
2answers
2k views

How do I properly wire a 5-wire thermostat? What is this ambiguous '4' label?

I took the old thermostat off, and had G,Y,W,Rc and '4' terminals connected to the Green, Yellow, White, Red and Black wires respectively. Voltage from Rc to G|Y|W was 24VAC as well '4' to G|Y|W ...
3
votes
1answer
365 views

Should I leave splices when pulling new thermostat wire?

My existing 4-wire thermostat cable comes out of the furnace, and each of the wires is wire-nutted to another wire. That then goes to the thermostat. I'm going to pull new cable to support a smart ...