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

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12 views

Replacement thermostats [on hold]

I have a commercial application with over 20 thermostats of various types and age. Over the years we have had individuals who feel it is their right to adjust them. We have tried putting them into ...
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1answer
43 views

Can I use Eneloop batteries in my thermostat?

I have this LuxPro thermostat http://www.luxproproducts.com/pdfs/spec_pdfs/PSD010Bc_NL_ENG_Manual.pdf There's a warning in the very first section that says to use only Duracell or Energizer Alkaline ...
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1answer
338 views

No electricity going to thermostat

Our old thermostat is working but I want to change to a new one (nest thermostat). I have two exact HVAC unit at home. I change one it works but when I change the second one it doesn't work because ...
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0answers
6 views

Zones and setback thermostats

I've got a two-floor house, forced-hot-water and traditional radiators, with a thermostat and zone for each floor. I'm working from home at the moment, so the ground floor is set up to be "office ...
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3answers
6k 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. ...
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1answer
467 views

Please help establishing a C wire for new tstat

I bought a new WiFi tstat as a replacement. The tstat controls my second floor hot water baseboard heat and my central air conditioning. I've located all the wires....the ones coming up from the ...
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1answer
27 views

thermostats for high desert climate

We live in Spokane, WA, a high-desert climate. We don't need a programmable thermostat, but we do need one to keep an constant ambient temperature range. This may mean A/C during the day, and heat at ...
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1answer
404 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 ...
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1answer
384 views

How can I add a C-wire to a Venstar T5800 thermostat?

I am trying to replace my existing thermostat. My old thermostat has: Rh, W (coming from the heating unit). Rc, Y, G (coming from the AC unit). On the Venstar T5800, I can map as follows: Rh+Rc ...
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2answers
103 views

Honeywell home ventilation system with no c wire for thermostat. How can I substitute the g for the c without blowing a fuse?

I'm hoping to get some help with my thermostat problem. We bought our home brand new and it came with a very basic thermostat (non programmable and runs on batteries). I want to upgrade it to a wifi ...
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1answer
320 views

why does my heat pump wiring diagram show 7 wires going to the thermostat but the thermostat only says it needs 5?

Here is a link to the wiring diagram for my heat pump. The thermostat that I am planning on buying has the following terminals C, G, Y, O/B, RC, R, Aux, E, and L. The instructions say to jump the RC ...
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2answers
51 views

Is the Nest thermostat smart enough to turn itself on BEFORE you get home?

I'm wondering if in "Away" mode, is Nest smart enough to learn about when you come home, and kick on approximately 30-40 minutes BEFORE then? Or does it only kick on when it senses you've come home? ...
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1answer
100 views

Zoned oil furnace and AC thermostat question

I recently moved into a new home and wanted to replace the old thermostats with digital Honeywell ones. From what I understand the home has a Rheem 10 Seer (1996) compressor and a Williams oil furnace ...
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1answer
115 views

How do I connect a C wire to an Utica PEG112CDE steam boiler?

I want to upgrade my old mercury thermostat that I currently have to a newer programmable thermostat. This little DIY project is for my first late 1920's home that I recently purchased. I currently ...
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1answer
43 views

Where do I connect the C wire in my furnace?

I am upgrading my thermostat to a Nest, and would like to add a common wire. My current furnace controller doesn't have a C terminal, but the current thermostat wire has 2 unused wires (black and ...
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0answers
58 views

Honeywell WiFi Smart Thermostat Wiring

The Honeywell WiFi Smart thermostat was operating fine when on AC until the heat went on this fall. Now, each time the fan goes on, the thermostat loses the connection, turns blank, then reboots ...
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1answer
79 views

How can I replace an old dial thermostat on an oil furnace with Hydrostat 3250 Plus?

I recently bought a home with an oil fired Biasi furnace that has a Hydrostat 3250-Plus attached. It uses an old analog round dial thermostat, and I'd like to replace it with a new digital (wifi) ...
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1answer
85 views

My attic unit already has a wire connected to C, can I still connect a wifi thermostat? [duplicate]

I have an extra wire I can use for the C wire on both ends but in my attic the main unit has a wire already attached to the C spot and going away from the unit to something else. Can I attach two ...
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3answers
7k 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 ...
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1answer
151 views

Where to add C wire on this air handler?

Thanks for helping me here. I am adding a new wifi thermostat to my system but need to add a C wire directly to the air handler (system is a First Co air handler with hot water boiler for heat and ...
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2answers
185 views

Where is my common wire on the unit?

I have 2 systems in my house, my heat is gas hot water radiator heating and A/C is a separate newer system. I'm trying to figure out if I can run a C wire off air handler from the A/C system to run ...
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1answer
59 views

Why did I have to change the wiring to use a smart WiFi thermostat?

I just installed a Emerson Sensi wifi thermostat.It works, and I ran a separate C wire. I had a 24 volt 5 wire Robertshaw programable thermostat that ran my boiler, air handler and AC. It is all ...
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1answer
130 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 ...
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1answer
242 views

Can I replace this Airwell thermostat?

I am in market to replace my simple A/C control unit with one that integrates with home my z-wave based home automation system. However, before I make the splash and buy a compatible thermostat, I ...
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0answers
15 views

Updating thermostats to single system

I have a three floors in my house, each controlled by it's own thermostat (separate air handlers and mechanical valves on furnace). Baseboard heat. The three thermostats are controlled separately, ...
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1answer
50 views

Deactivate thermostat [closed]

I have a roommate that constantly turns the thermostat down to 65 during the winter months. Is there a way I can deactivate it, while maintaining a comfortable 72?
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2answers
314 views

Where to attach the “C” wire to my furnace?

I am upgrading to a new thermostat which requires a "c" wire to power it. I have an unused blue wire running from my thermostat to my furnace that I plan to use as the common wire. However, I am ...
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0answers
128 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 ...
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26 views

How can I install a Honeywell Linevolt Pro 8000 in a multiple thermostat situation?

My roommate who just moved out installed a Honeywell Linevolt Pro 8000 in his room several months ago (replacing an M602 with no brand name that I can find) and it seems to have worked fine - it had a ...
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2answers
1k views

Can you terminate more than one common on the furnace C terminal?

TL;DR: Can you terminate more than one common on the furnace C terminal? Background: I've linked a diagram of how my non-programmable thermostat is currently hooked up. I want to replace it with a ...
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3answers
2k views

How can I modify a 4 wire thermostat to a new thermostat requiring c wire?

I attempted to replace my thermostat with a fancy new Trane z-wave enabled model. To my dismay my home was only wired with a 4 wire setup with no 5 hidden in the bundle. I followed Insx on the web ...
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3answers
8k 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 ...
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1answer
217 views

How can I install a Honeywell RTH65800WF Wifi thermostat?

I am having some difficulty figuring out the correct wiring for my new wifi thermostat. Before I bring out the A/C technician, I was wondering if anyone here might be able to help? Searched other ...
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4answers
6k views

HoneyWell Wifi Thermostat and C wire

I just bought the HoneyWell Wifi thermostat and so wanna use it. However my old Thermostat was battery powered and does not use the "C" wire. I opened up my panel and found that there were three ...
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2answers
65 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 ...
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2answers
38 views

Is it possible to create a better temperature controlling system?

I have a two story 2.5k sq ft house with a varying degree of temperature throughout the house. The main problem is that the air coming out of vents are very weak if almost nil. Only the living room ...
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0answers
362 views

Where to connect a c-wire on a furnace with existing two wire mercury thermostat

My existing thermostat is an old mercury two wire device, heat only. Looking to upgrade to a better model, but I need to run a c-wire. I don't know where to connect the wire at at the furnace, any ...
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2answers
790 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 ...
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0answers
31 views

Keep finding thermostat on heat

On multiple occasions now, I have noticed odd things going on with my HVAC system, only to go to the thermostat and find that it has been set to heat! This happened once in the middle of summer, when ...
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1answer
34 views

Should my A/C compressor come on when I turn only the fan on?

I have a bog standard HVAC system with a Nest thermostat. When I tell the theromostat to turn the fan on for 15 minutes the A/C compressor also kicks on. Is this normal?
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1answer
27 views

choosing a programmable thermostat: wiring and power

I want to replace my non-programmable RobertShaw 9500 thermostat with a programmable thermostat. The current wiring uses these terminals: RH, W, Y, G. With that set of wires, can I get a ...
5
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2answers
14k 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 ...
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1answer
156 views

Replacement thermostat wiring

I have an American Standard heat pump AC. I'm replacing a White-Rodgers manual thermostat (where I move a switch from cold to heat) with a Honeywell RTH7600 (which will automatically switch from cold ...
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0answers
14 views

Why does adding 2nd Wifi thermostat not work in 3 zone home?

Our home has 3 zones for forced air heating by oil and central AC. I replaced a Robert Shaw thermostat with a Honeywell Wifi unit and it worked fine. I then replaced another Robert Shaw thermostat ...
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1answer
40 views

How do I determine/control which heat source is used (heat pump, oil)

I have a heat pump and an oil furnace for backup. How does the HVAC system know when to use the heat pump and when to use the oil furnace? Specifics: I have a Honeywell TH8320U1008 thermostat ...
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1answer
419 views

Which terminal should be used for a “C” wire when none are labeled “C”? Older electric furnace/heat pump

I have an all electric air handler/furnace connected to a separate AC unit and it is also a heat pump. I've purchased the latest and greatest Honeywell WiFi "Smart" Thermostat and it needs a C wire. ...
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0answers
163 views

Furnace not working properly with digital thermostat

I have been attempting to use several different types of digital thermostats to replace my old mercury thermostat, however none of them are able to control the furnace properly. All of them are able ...
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2answers
23k 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 ...
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2answers
78 views

thermostat batteries replaced, AC unit won't start

Came home from work to find no AC. I checked the thermostat and the display was blank. After replacing the batteries and resetting the program, my AC unit never started up. I checked: - The AC unit ...
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1answer
74 views

How to connect a DIY thermostat to the HVAC System

I am building a DIY thermostat similar to this blog. I want to connect it to the HVAC system of my home. How do I do that? I found this post which is very informative but doesn't completely answer my ...