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

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54
votes
5answers
261k 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 ...
16
votes
4answers
30k 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
22k 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 ...
8
votes
1answer
26k 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 ...
7
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
3answers
2k 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 ...
5
votes
4answers
3k 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
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
13k 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 ...
5
votes
1answer
149 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
1k 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
5answers
41k 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
2answers
2k 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
24k 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
1answer
7k 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 ...
4
votes
4answers
9k 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
4k 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
8k 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 ...
4
votes
1answer
94 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
3answers
1k 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
2answers
20k 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
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 ...
4
votes
1answer
617 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
1answer
158 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
1answer
11k 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
5answers
74k 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 ...
3
votes
3answers
45k 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
4answers
10k 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
1answer
784 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
2answers
3k 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
3answers
12k 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
19k 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 ...
3
votes
1answer
556 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
786 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
135 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
38 views

How do I turn off the power to my thermostat?

I'd like to replace my thermostat with a new one. My current thermostat is one that doesn't have a C-wire and is powered by batteries. Now, my question is... is there a switch for the power that I ...
3
votes
1answer
204 views

New Thermostat Ecobee3 to Old Galaxy GG-75 boiler - Needs common wire

I would like to replace my old thermostat with a new Ecobee3 thermostat. HVAC system is a Slantfin Galaxy GG75 boiler - single zone. (No air conditioner.) Current set-up has only a red and white ...
3
votes
1answer
469 views

Can I connect an additional wire to HVAC system where all the terminals are full?

I'm installing a new thermostat (ecobee Smart Si) and it requires "C" wire. I checked before I bought, and saw an unused blue wire behind my current thermostat. However after connecting everything the ...
3
votes
3answers
317 views

Can a furnace with a variable speed blower be used in a multistory house?

I just had an HVAC guy out to give me an estimate on a new Carrier Infinity series furnace and he said the second floor rooms will always be colder because the thermostat is on the first floor and not ...
3
votes
1answer
5k 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 ...
3
votes
1answer
1k 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
2answers
1k views

Hvac Fan only blows in 'fan on' mode while heating

Our HVAC Fan only blows in 'fan on' mode while heating. In other words the fan will not blow in heat mode if switched to "fan auto". Both fan on and fan auto modes work when cooling. See image below, ...
3
votes
2answers
454 views

How do I wire this 240v fan motor and thermostat

I'm trying to wire a two stage exhaust fan for my greenhouse. The motor comes set up for 240v wiring and is to be controlled by a thermostat. I undertsand how to get the 240v from the panel, but can't ...
3
votes
1answer
87 views

Is it OK to leave the thermostat unwired?

So I went to replace the batteries in my thermostat and when I pulled it off I noticed a black wire was unplugged. I'm not sure if it's suppose to be like that or if I accidentally pulled the black ...
3
votes
2answers
4k 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 ...
3
votes
1answer
64 views

1 nest to control all vales on UFH manifold?

We are having an extension done and intend on having all underfloor heating in the new area. Currently we have a valiant combi boiler supplying the main house which has been T'd off with a valve for ...
3
votes
1answer
146 views

Why does my gas furnace run once then wont come back on until reset when temps are below 30 outside?

THE PROBLEM: My gas furnace will run one cycle and then not come back on until the switch is reset. Once the switch is reset it will kick on immediately run once and again I will have to reset before ...
3
votes
0answers
479 views

How do I install a WiFi thermostat with a Well-McLain steam boiler?

I have a Weil-Mclain 150000 BTU steam boiler, and have only 2 wires connected to my thermostat, but would like to add a new Honeywell WiFi thermostat. I have no C wire, no A/C, or any other type of ...
2
votes
2answers
964 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 ...