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

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34
votes
4answers
117k 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 ...
14
votes
4answers
9k 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 ...
11
votes
2answers
7k 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 ...
6
votes
4answers
2k 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 ...
5
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 ...
5
votes
1answer
131 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
627 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
1k 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 ...
4
votes
5answers
19k 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 ...
4
votes
3answers
1k 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 ...
4
votes
4answers
3k 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
4answers
841 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 ...
4
votes
2answers
9k 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
4k 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 ...
4
votes
1answer
987 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 ...
4
votes
1answer
190 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
2answers
585 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
1answer
141 views

Is it possible - setting thermostat based on a seperate 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
2answers
11k views

What should I use to wire a 220v electric baseboard heater and thermostat? 12/2 or 12/3

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 ...
3
votes
3answers
4k 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
3answers
11k 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 ...
3
votes
1answer
565 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
3k 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 ...
3
votes
2answers
1k views

Can I piggyback a thermostat with a C Wire hookup on a furnace?

I'm trying to install a new thermostat that needs a C wire hookup. There are currently 4 wires running from the thermostat to the furnace, none of them are a c wire. When I look at my furnace itself ...
3
votes
2answers
5k views

Why does the gas furnace blow cold air at the start of the heating cycle?

What does this problem sound like? There is a 25 year old gas furnace in the house we rent. (The guy that owns the place claims there is NO problem at all. He said the igniter is brand new and ...
3
votes
2answers
1k 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 ...
3
votes
1answer
322 views

Should fan on heat pump be delayed turning off when system stops?

I have a heat pump system with emergency heat. I have a Honeywell RTH7600D thermostat. When the heat is running and I turn the temperature down, the system immediately stops. Isn't this inefficient ...
3
votes
2answers
3k 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 ...
3
votes
2answers
510 views

Can I use an unused wire as a “C” wire?

I just bought a new thermostat that is Wi-Fi enabled and it requires connection to a "C" wire. The old thermostat does not have one running to it, but there are other unused wires. The thermostat ...
3
votes
2answers
2k 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 ...
3
votes
1answer
121 views

How come the temperature is sometimes not maintained?

First let me come right out and say that I am a software guy and this seems like a hardware problem, so I already feel out of my league. That said, here's the deal: Background: I have two-zone "hot ...
3
votes
1answer
322 views

How can i figure out which wires go where, if the colors at the furnace don't match the thermostat?

I have an old system and want to update the thermostat however, the white-rodgers thermostat has no letters such as R,G,B,Y,W,C So I checked out the furnace terminate wires and the colors of the ...
3
votes
1answer
5k 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 ...
3
votes
2answers
1k views

Trying to wire a 240v line-voltage thermostat

I am trying to replace my old 240v line-voltage thermostat with a modern version. The problem is that after wiring the new version in like the old it doesn't work. I have (2) 12-2 wires coming out of ...
2
votes
2answers
723 views

Using a solar system with a condensing boiler for the central heating instead of tap-water?

According to the manual of my AWB ThermoMaster 2HR 28.02WT Condensing boiler, it is compatible with a pre-heating solar system for tap-water only. It even has extra facilities to ensure that the ...
2
votes
1answer
2k views

Can I pair two thermostats to work with a single zone system?

I have a southern California two-story home built in the late 70's. Its a single zone system with both heating and AC. The thermostat is located downstairs. In the summer the upstairs gets too ...
2
votes
2answers
3k views

Why is my A/C unit running when the heater runs?

So it finally got cold here in AZ. We switched our thermostat from A/C to Heat. Now for some reason when the electric heater runs, the A/C condenser unit outside kicks on too. This is our first winter ...
2
votes
1answer
142 views

When I set the thermostat to X degrees, is that the temperature at which air is pushed out through the vents?

My hunch is that most ac units aren't that sophisticated, and they just pump air that is "cold enough" or "hot enough" and pump it until temperature rises to the specified value. Is that right?
2
votes
1answer
2k views

How do I properly install a replacement thermostat in my refrigerator?

My fridge stopped cooling - compressor was always off - so I tested if the thermostat could be the culprit by bypassing it - bang, compressor powered on. So I bought a new thermostat. It is not ...
2
votes
1answer
128 views

Is there a way to make a thermostat based heating system more accurate through either adding probes or hacking?

In my Brooklyn apartment, heated via steam radiator, my thermostat is in the unheated hallway between all the rooms. The temperature it reads is often different, than both the rooms with heaters and ...
2
votes
1answer
298 views

Will I see any performance gains if I reconfigure my thermostat to control the second stage of my 2 stage furnace?

Our furnace is a two stage one that was installed last year (a Bryant 80t). When it was installed, it was installed with a thermostat for a one stage furnace. This appears to be because this model ...
2
votes
2answers
3k views

How can I tell what kind of heating system I have?

Seems like a simple question, but I've had a very hard time finding a definitive answer to this. I went to the hardware store to buy a replacement for a faulty thermostat and when I arrived and ...
2
votes
1answer
840 views

What is causing the high limit switch to pop on my electric water heater?

The high limit switch has popped twice on my electric water heater, both times at night. I reset the switch and the water heats and it's ok throughout the day. Wake up in the morning and it's ...
2
votes
1answer
70 views

Can I insulate between a brick chimney and drywall?

Can I insulate the space between a brick chimney and the drywall inside my home? I am getting heat transfer from the brick to the drywall in the summer from the sun heating the brick. My thermostat ...
2
votes
1answer
500 views

Is it possible to control the speed of the fan on my central A/C unit?

I have one of those medium sized AC-units (don't know the model name at the moment) and a very basic Honeywell thermostat that the installers put in when the house was built. However, there doesn't ...
2
votes
1answer
239 views

What could be damaged if I shorted the R wire to the C wire at my thermostat?

OK... so in trying to install a thermostat (and testing to see if the old thermostat was bad) I inadvertently jumped the R and C... (I actually jumped the R and G terminals but the G terminal was ...
2
votes
2answers
5k 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. ...
2
votes
1answer
241 views

HVAC electric thermostat panel “goes dead” and then live again all the time

I have this digital thermostat controlling my heater (gas). When I turn it on to lets say 66 deg, and the house is at 60, the HVAC will start working of course. Problem: After few minutes, the ...
2
votes
0answers
199 views

Are w1 and w2 both energized during a second stage heat call from the thermostat?

Short version: does two-stage thermostat always close W1 circuit when it closes W2 circuit, or they might be closed independently? Long version: I have two-stage furnace, currently connected to older ...
2
votes
1answer
3k views

How can I add a “C” common wire to this system? [duplicate]

I would like to add a "C" / Common wire hookup to my hvac system and get a fancy new thermostat. I've read Options for adding "C" wire to thermostat and still have some questions. First of ...