Attic fan

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Feb 14, 2004
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My attic has a thematically controlled fan up there. What is the best temperature to have it come on? I set it @ 70 deg. this year. At 8:30am it came on. I’m wondering what time it will cut off, probably 12pm. In the hotter months it will probably run non stop.
Dean
 
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Is the attic insulated (ie: insulation on the attic roof) or is the ceiling insulated (insulation on the attic floor)? If the attic is insulated keep the fan off. If the ceiling is insulated simply set the temperature at what the average outdoor high temperature will be.
The idea is that the fan keeps the temperatures from getting too high. There is no point in setting the temperature lower than the high outdoor because the fan will never shut off. Set it at outdoor high temperature and when the attic gets hotter than outside temperature the fan comes on and brings the cooler outdoor air in to cool the attic off.
 
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The ceiling is insulated. The average high temp will probably be 90deg. this year. I have a dark forest green metal roof and it heats up quickly in the attic. So my thinking is move the air through as soon as it is getting hot in the attic. It’s now 9:30am and it 70 out side, but the fan was on for an hour already. I’m just trying to keep it a cool as possible. We don’t have an AC, as it is not necessary at our altitude with dry air. We also have a whole house fan that sucks the air form the house and pushes it out the attic. At night the temps drop fairly quickly and the attic fan work well to cool the house.
Dean
 
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The idea is that the temperature in the attic remain as low as possible so the inside doesn't become hot due to heat transfer. Obviously turning the fan on too soon uses extra energy but too late and the attic is hot. If you set the temperature for 70 but it's 90 outside the attic can never get cool, and the fan will run until the attic is 70 or less (keeping you awake at night while doing so). Set it to 90 which is the hottest it would normally get outside and it might shut off once and a while (but not unless the attic is 90 or less).
Do you have a "Swamp cooler"?
 
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I have two fans

And from the research I did, I set the thermostat around 95 to 100 degrees. The thermostat's are mounted onto the roof beams, about 3/4's the way to the peak.

When it'll be a hot day, the fans kick on late morning, 10-11, and may stay on past 10 PM bedtime if it is still 75 degrees outside.

If it is hot at bedtime I open the 'ladder-door' to the attic to let heat from inside flow up into the attic, sort of like the 'whole-house-fan' idea.

I also have a switch inside the house to kill power to the fans, so I leave them off until I'm worried about over heating the home. (Like in the winter)

I think this temperature choice/location of the thermostat works well, keeps the balance between keeping the house cool, and running all the time.
 

krzyabncanuck

USFS HOTSHOT
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Not to barge in but i was about to go buy a fan for my attic. But you all say that I really do not need one if my insulation is on the floor in the attic. Heck you might of saved me some money. I live in NC, but not in the mountains and it will get at least 100 + here this summer.

TIA.
 
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krzyabncanuck said:
Not to barge in but i was about to go buy a fan for my attic. But you all say that I really do not need one if my insulation is on the floor in the attic. Heck you might of saved me some money. I live in NC, but not in the mountains and it will get at least 100 + here this summer.

TIA.
Nope, the other way around. You don't need, or want one, if the insulation is on the roof of the attic. If the insulation is on the floor of the attic then you can make use of one.
 
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calamaridog said:
What if you have insulation on the roof and the floor of the attic?
It doesn't matter. The insulation under the roof surface helps to keep it cool inside, but it can also keep the heat in during summer. Having a whole house fan helps to bring in the cool evening air, and the cool morning air. It's a quick purge, and not meant to run all day.
An attic fan can run all day and effectively cool the house. Even if the temps outside get up to 115 degrees, the attic may reach 140 plus. By bringing in the 115 degree air, you are dropping the temp in the attic and using conductive cooling at the same time. The attic temps will drop making the house more comfortable.
Now, having said all of that, you need to make sure that the attic fan works efficiently. How is that done? By providing enough open vent space around the soffits, rafter tails, and eaves. Even gable vents and whirlibirds on the roof allow ventilation. When purchasing an attic vent, look on the box and it will indicate how many square inches of ventable space is required.
If you were to tilt a jug on end, it goes glug, glug (not to be confused with a gub which is entirely different animal), when the fluid pours out. Punching another hole in the jug removes the vacuum, allowing the fluid to flow out smoothly. The same principle works with an attic fan. It only works efficiently if there is enough ventable space to allow the air to flow smoothly. Attic fans are one of the cheapest ways to cool down the house.
 
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krzyabncanuck said:
How hard are they to wire in ?
Piece of cake. They are hard wired and no switches are involved. Most codes call for an independant circuit, but most jurisdictions allow tapping into an existing continually hot section of romex, tying it into a junction box and the fan unit. I'd set the thermostat at around 90-100 degrees or it will run almost constantly. Adjust for comfort. Humidity will vary the comfort level so adjust accordingly.

As for a gub infestation, catching them on a pink bedspread with polka dots, snapping their pic, and posting it on Mud, will keep them in line. Vintage gubs are especially tricky, but can be dealt with using these effective techniques. That or you can ship all of your gubs to CDan. He'd happily take them off your hands. :D
 
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PabloCruise said:
Humid?!? In ABQ??? I call BS on that one!
It’s not humid like some of you are used to. But we have about 2 months that are humid due to the rain. I also live in the Mountains East of Albuquerque at 7200ft. that’s why we can get away with out AC.
 
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Jan 22, 2003
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San Diego, CA
 
 
 
White Shark said:
Even if the temps outside get up to 115 degrees, the attic may reach 140 plus. By bringing in the 115 degree air, you are dropping the temp in the attic and using conductive cooling at the same time. The attic temps will drop making the house more comfortable.
I know about that- I had to change the belt on my attic fan yesterday 120 deg. up there :doh: Vacuumed layers of dust off the blades and it makes it much quieter, less rattling and vibration.
I rent (been here for a month) and Im guessing the landlord has never heard of preventative maintenance for this place
this is the A/C filter :rolleyes:
 
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