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Attic Fan Runs in the Winter Chicago IL
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posted
I live in Chicago IL, and have a electric attic fan that seem to run a lot more often than before.

It is currently about 45 degrees here.

The fan does have a humidistat and thermostat.

Is this operation normal?

In the early fall it was also coming on at about 3am?

My attic also has gable vents and i think soffit vents.

Thanks,

Ryan
 
Posts: 3 | Location: IL | Registered: 19 November 2007Reply With QuoteReport This Post
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The fan should run both when its hot and when its humid. What is happening in your case is common.
As the outside air is warm during the day the humidity level begins to rise as more moisture is evaporated into the air. While the outside temps begin to rise in the attic the fan begins to run. This then pulls in the warm moisture laden air with it. As the air outside begins to cool towards the evening the humidty level begins to rise as the air begins to condense. You can see this outside as moisture on your cars and on the grass. The humidistat sees this moisture before it condences to water. And continues to run the attic fan until the outside air that is being pulled into the attic has lost enough moisture that will then turn off the fan.
Without this fan you would find water stains on the nails that poke through the roof. In some cases if the outside gets cold real fast you will find ice on the wood along the eaves. All of this moisture will cause mold in the future. The fan will help prevent this from happening.
Its doing exactly what it is supposed to do.
 
Posts: 1933 | Location: New Jersey | Registered: 31 January 2006Reply With QuoteReport This Post
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I think however that the humidistat may be bad, as the fan ran all through the night and all through the day without shutting off. The humidistat is set at 70 percent. and the only way to get the fan to shut off is by turning the humidistat to stop.

Even last winter i don't remeber it running this much, and i know that i did not change any attic insualtion.

Is it still normal that this thing runs 24/7 it would seem like it would regulate it at one point or another.

Thanks,
Ryan
 
Posts: 3 | Location: IL | Registered: 19 November 2007Reply With QuoteReport This Post
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Could be a bad control. But the weather may also be the issue. I do think however if you aready have good ventilation then why did the fan be installed in the first place. If you want do not run it at all. But if you decide to run it be sure that both controls are working. A fan without the humidistat will cause more issues then one not working at all.
 
Posts: 1933 | Location: New Jersey | Registered: 31 January 2006Reply With QuoteReport This Post
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It was reccomended that i install one by the home inspector who looked at the house, there were signs of moisture some time ago on the plywood under the roof. In addition we had both shower fans put in and they come out in the attic right under the fan. I guess they figured that it would be good to get that added humidity out. It was still on last night so I went up and checked the settings and the temp was set at the manufactureres ideal seeting of 105, and the humidistat was set at 70 percent. I even tried turning the humidistat to a higher percentage, but it didn't seem to do anything.

Ryan
 
Posts: 3 | Location: IL | Registered: 19 November 2007Reply With QuoteReport This Post
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The shower fans should NEVER discharge in the attic. That is fundamental. They should be directed to wall or roof caps, as appropriate, equipped with backdraft dampers. Never NEVER in the attic!


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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Go to Radio Shcak and buy a thermogygrometer for about $20-30. Place it next to the thermostat. When the fan turns on, check the temperature and relative humidity reading on the meter. That will tell you if the thermostat or humidistat is bad.

As Richard said, do not exhaust into the attic.

It is also not a good idea to exhaust the attic during the colder months of the spring and fall, and certainly not during the winter. While some of the exhausted air will come from the soffit and gable vents, some will also come from the living spaces. It's a waste of energy and also likely to cause condensation problems in the attic.

Were the "signs of moisture" on the sheathing before you added the bath exhaust fans? If so, assuming the soffit and gable vents are sized correctly, there is likely some fairly large amount of leakage area between the living area and the attic which is allowing the warm humid air from below to get to the attic. You can find a weatherization company with either a blower door or infrared scanner to find and seal those leaks.
 
Posts: 13 | Registered: 31 January 2007Reply With QuoteReport This Post
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Like Richard said do not vent bath fans into the attic. Also when correcting this be sure to use insulated ducting for the fan. As any moisture in the vent pipe will condense if cooled to quickly in the winter months. This will cause water to build up in the ducts and mold will develop
 
Posts: 1933 | Location: New Jersey | Registered: 31 January 2006Reply With QuoteReport This Post
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