# wiring thermostat controlled attic fan



## rjniles (Feb 5, 2007)

Easy, Run a 2 wire cable from the fan to the switch box, install single pole switch. At fan connect wires across the contacts of the t-stat. Run a wire the same gauge as the existing wiring. 12-2 for 20 amp circuit, 14-2 for 15 amp circuit.


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## mazey (Jan 27, 2011)

thanks, not sure if i asked question correctly. i want the fan to always be "on"(thru the fan mounted thermostat), but i want to be able to remotely bypass the thermostat and turn the fan on by a switch from time to time.and then turn it back to t-stat control. fan is on single 15amp circuit with14 gauge wire. when i go up in the attic to move stored items around, it would be good to get some air moving around , and i dont want to have to reach for the t-stat ( hi up in the rafters)


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## rjniles (Feb 5, 2007)

What I said in my post will do what you want. With the switch off the t-stat will control the fan, with the switch on the fan will run regardless of the temp. Run with 14-2 NM cable if it is allowed in your locality.


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## HVAC_NW (Oct 15, 2007)

The thermostat operates the fan by making a connection between two wires. When you put a switch parallel to these two wires, closing the switch bypasses the thermostat.


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## mazey (Jan 27, 2011)

think i got it, had to draw myself a diagram. the t-stat is hot, but the switched 14/2 is only used to jump the t-stat? i'm gona upload a diagram, thanks. i was thinking of using a single pole double throw switch


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## rjniles (Feb 5, 2007)

mazey said:


> think i got it, had to draw myself a diagram. the t-stat is hot, but the switched 14/2 is only used to jump the t-stat? i'm gona upload a diagram, thanks. i was thinking of using a single pole double throw switch


A single pole double throw switch is a 3 way switch. You do not need that. You need a regular single pole switch. (SPST)


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## mazey (Jan 27, 2011)

3 diagrams, existing, option "a" is what i thought would work with a on-off-on switch that feeds the fan or option"b" which is what i'm interpreting from rjniles, where the fan is fed seperately and i have a single pole switch that closses the t-stat. any way better than the other? i'm replacing the wiring anyway, and the walls open. thanks


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## rjniles (Feb 5, 2007)

Your options are both the same but B is more correct. Remark the white wire as black (not on the diagram but on the actual wire).


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## HVAC_NW (Oct 15, 2007)

Option B gives you manual on override. 

Option A, you would feed the hot to center, then one of the connection to thermostat, other one direct to fan and this gives you forced off, thermostat, and forced on. You'll need one with a center stop though. They're very common in electronic circuit building, but I'm not sure if they have on-off-on type switch for house wiring


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## mazey (Jan 27, 2011)

right,black tape on white wire to indicate its not a neutral,. i had to see it on paper first. good thing because no electrical supply around me stocks the switch i needed for the double throw. am i the only person who wanted to control a fan like this? seems like a good idea to me. thanks again


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## mazey (Jan 27, 2011)

just 1 more question , what if i throw the "extra " switch closed, when the fan is already running because the t-stat was "closed"? would i just have an extra leg of "hot "wire? any reason for something to short out or trip breaker?


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## HVAC_NW (Oct 15, 2007)

You can find center off SPDT at Radio Shack with more than adequate capacity for a fan and it will work, but they are for system integration, so if you use it for home wiring, it won't be up to code. To mount it, you'll need to get a blank cover plate, then drill a hole in the middle, or if it's the right size, you can probably use the cover plate meant for CATV hookup. 

To do it with home wiring switches, you'll probably have to use a dual ganged SPST switches and use one for on/off, then the second for auto/on. The on/off has to be on for either on or auto to work.

If it's an electronic thermostat without a neutral, the bypass switch will deprive it of power source and cause it to lose settings and/or clcok. If it's one with a neutral or a mechanical one, the thermostat will continue to turn on/off without having any effect on the fan.


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## mazey (Jan 27, 2011)

HVAC_NW said:


> Option B gives you manual on override.
> 
> 
> what is meant by "manual on override"


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## rjniles (Feb 5, 2007)

Just realized waht you were trying to do with option A. Yes that will work but you need a 3 wire cable from the fan to the switch box. Remarked white to power the switch and red and black as switched hots back to the fan.

Rather than try to find a single pole, double throw, center off switch as you show (not real common), consider 2 single poles switches in a 2 gang box. Or a 2 single pole combination switch (2 switches on a single yoke that fits in a single gang box.).


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## mazey (Jan 27, 2011)

thanks, was figuring on option b, have it all wired up and working ok,on thermostat all time and then i flip switch to bypass t-stat and fan runs. in my head though just because something works, doesnt mean its correct, anybody see anything wrong with this setup? maybe the t-stat is going to short out or something? thanks


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## morebytes (Jun 18, 2011)

mazey said:


> thanks, was figuring on option b, have it all wired up and working ok,on thermostat all time and then i flip switch to bypass t-stat and fan runs. in my head though just because something works, doesnt mean its correct, anybody see anything wrong with this setup? maybe the t-stat is going to short out or something? thanks


My wife and I just had our roof replaced, and the crew dismantled and threw away our attic fan. After back and forth, the roofing contractor attempted to rectify, but in the process has not been able to restore our ability to use our manual switch in upstairs hallway, that from time to time helped create some airflow in the home, transferring cooler downstairs air to upper floor. Sadly, now they can't figure out how to reconnect so that we have both the thermostat AND manual switch access. Just today I added the iPhone app for this site and was more than pleased to find at least one other person with this arrangement. Your diagram was helpful, and will probably allow for a remedy. Thanks "mazey" and "rjniles" and "HVAC_NW." I'm glad this community exists. --Kevin


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## mazey (Jan 27, 2011)

just the other day i was in attic working on plumbing and it was nice to get some air flow by manually turning fan on even though it wasnt hot enough for t-stat to kick on.since the fan is in a hard to get to spot, i have the switch in a more accessable location . goog luck


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## mpj (Aug 17, 2011)

mazey,
I have the exact situation in my attic, but I do much better with pictures (have a hard time understanding the diagrams). I know this is asking a lot, but could you take pictures of your switches & wiring and post them? I understand it that's asking too much. thanks a bunch.


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## picflight (Aug 25, 2011)

mpj said:


> mazey,
> I have the exact situation in my attic, but I do much better with pictures (have a hard time understanding the diagrams). I know this is asking a lot, but could you take pictures of your switches & wiring and post them? I understand it that's asking too much. thanks a bunch.


Me too, love to see the picture as well.


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## picflight (Aug 25, 2011)

morebytes said:


> My wife and I just had our roof replaced, and the crew dismantled and threw away our attic fan. After back and forth, the roofing contractor attempted to rectify, but in the process has not been able to restore our ability to use our manual switch in upstairs hallway, that from time to time helped create some airflow in the home, transferring cooler downstairs air to upper floor. Sadly, now they can't figure out how to reconnect so that we have both the thermostat AND manual switch access. Just today I added the iPhone app for this site and was more than pleased to find at least one other person with this arrangement. Your diagram was helpful, and will probably allow for a remedy. Thanks "mazey" and "rjniles" and "HVAC_NW." I'm glad this community exists. --Kevin



Thanks to the two of you for posting here, I am in the process of replacing my attic fan and adding a manual override is an awesome idea. I will be adding an outlet and light in the attic as well. My attic is not large by any means and I would be mostly crawling in there, even if I am in the attic once a year, it will be nice to have a light and fan.


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## mazey (Jan 27, 2011)

sorry for responding late, would be tough to get a picture of switch wiring. best thing is working with the diagram i made up. its alot more clearer than a pic of wires , thanks


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