Attic Fan override switch - wiring help

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  #1  
Old 01-01-15, 09:19 PM
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Attic Fan override switch - wiring help

Hi,

I have an attic fan that runs off a thermostat (the gable fan type). I would like to install an override switch in order to manually turn it on during the winter. I am hoping the extra airflow in my attic will help with ice dams.

Can anyone help suggest the best way of wiring this? I attached an image with two possibilities that I can think of (apologies in advance for my handwriting!). A friend said Option 2 would be better than Option 1 in the rare case both the override and thermostat are on, but neither of us are experts in this.

Any help is greatly appreciated. Thanks!

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Old 01-01-15, 09:38 PM
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Welcome to the forums.

To answer your question about the wiring of the fan... not to agree with running the fan in the winter.

When I wire those fans I use a piece of three wire cable. Your option two basically shows that. You can use a three way switch. One position will turn the fan on and the other will put it in auto mode.

I use a three position toggle switch..... up is on, center is off, and down is automatic.

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  #3  
Old 01-01-15, 09:50 PM
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Either circuit will work equally well. I do question running the fan in the winter. In fact, a properly air-sealed attic with proper ridge and soffit venting should not need any fan at all regardless of season.
 
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Old 01-02-15, 08:54 AM
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Do you have ridge vents and soffit vents? If so don't use a gable fan,I can tell you from experience,mold can create a COSTLY EXPENSE! I would check with others first.
Geo
 
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Old 01-22-15, 07:27 PM
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Hi, thanks so much for the responses. PJMax - I wired as you suggested and it works perfectly, and the three wire cable made it look very clean. I agree the attic fan shouldn't be necessary for winter storms, but my roofer suggested it as a simple fix I could try, and I'm out of other options. I have soffit vents and two layers of batt insulation. I don't want to go through the expense of putting better blown insulation in yet, so I'm trying this first. Thanks again for all the help!
 
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Old 01-23-15, 06:01 AM
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I have soffit vents and two layers of batt insulation. I don't want to go through the expense of putting better blown insulation in yet, so I'm trying this first.
This is off the subject of wiring the fan, but I just don't see what relationship there is between needing more insulation and running an attic ventilator in the winter.

By the way, if the fan is hardwired I hope you also installed a service switch at the fan.
 
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Old 01-23-15, 06:13 AM
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Are your soffit vents free and not blocked with insulation batts?
Geo
 
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Old 01-29-15, 07:36 PM
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Hi CasualJoe / Geochurchi - I have a switch that shuts off power to the whole attic. That's what I'm using as the service switch.

Here's the logic for the attic fan and preventing my ice dams:

My understanding of ice dams is that they usually happen when it's below freezing out, but the roof is warmer causing the snow and ice to melt. Then the water runs down towards the gutters. If the soffit and gutter area of the roof is still cold, the water re-freezes when it hits there and pushes back up under the shingles. This has happened to me twice recently, causing water to leak through my ceiling. I needed to sand the drywall, re-paint, etc. It was a pain.

So, I already have plenty of insulation in the attic (two layers of batt insulation). So I'm not going to be able to reduce the amount of heat from going up into the attic and roof without a significant expense there. In addition, I already have vents in my soffits, and those vents are clear of insulation (I have baffles to keep the insulation away). So the airflow should be pretty good.

So, a relatively cheap idea is to turn on the gable attic fan. Hopefully, that will force more fresh cold air up through the soffit vents, through the attic, and out the gable. Hopefully this will keep the entire roof a more consistent cold temperature, and stop the snow and ice from melting and running down in the first place. I have no idea if it's going to work or not. A roofer I know suggested trying it, since it's cheap, and there's really no downside to doing it.

Of course, any other suggestions are definitely welcome!

thanks
 
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Old 01-29-15, 08:19 PM
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We're really getting off topic here but I have to make a comment.

A roofer I know suggested trying it, since it's cheap, and there's really no downside to doing it.
Actually there is.... it appears that you may have poor airflow thru the attic and the attic fan will also be pulling warm heated air from the house. Yes, the attic will stay cold but at what cost ?
 
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Old 01-30-15, 08:59 AM
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A roofer I know suggested trying it, since it's cheap, and there's really no downside to doing it.
Did the roofer also suggest a ridge vent? Soffit vents are necessary for a ridge vent, but it sounds as if you already have them.
 
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Old 01-30-15, 05:27 PM
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Not a good idea as I stated before,if you have plenty of insulation as you say that should be keeping the heat in the living space,my roofer suggested the ridge vents and I let him install,at first I had no roof vents then had to cut them in,if you go your planned route make sure you check for mold frequently, it's costly to remove.
Geo
 
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