Ventilations and Fans

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  #1  
Old 06-21-15, 11:00 PM
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Ventilations and Fans

What is the proper way to vent a HOT room?

Before I ask the questions, I am going to provide a scenario.

I have a room 20x15 feet. There are two windows in this room. Each window is on the opposite wall of each other in this room. When I place my two fans for the two windows, is it best to place:
both fans blowing outward
OR
where one blows outward and one blows inward (Wind Tunnel Effect)
If you recommend the later (Wind Tunnel Effect) of the two, can I do this for the attic fans for the gables? The way how a fan for a gable works is always blowing outward.

Last question: I currently have two gable fans in the attic. Those are compliant to use in the attic because they have shutoffs when the fans get overheated. Is it safe :NO NO NO: to run a regular box fan (made of plastic blade) in the 110+ degree in the attic? Will the heat melt the plastic around the wires?
 

Last edited by WRDIY; 06-21-15 at 11:30 PM.
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Old 06-21-15, 11:41 PM
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Normally you would only use one fan. Open both windows, put one fan in one window blowing out. It will draw air in the opposite window.

Same with the attic. Fresh air vent in on one side of the attic and the gable fan blowing out on the other side.
 
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Old 06-22-15, 02:13 AM
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The recommended way to deal with heat in an attic is to insulate and ventilate the ceiling between the house and attic. In addition to all of the holes drilled for electrical wires there are often major pathways where large amounts of inside air is lost which in turn requires outside air to replace it, not good.

If the ceiling is not well air sealed there will also be a penalty for operating those attic fans in that they will increase the loss of air from the house.

If you have the recommended amount of soffit vent area, then 2 fans is certainly one too many. Tell us what other vents you have besides the two gables, ridge, soffit, or other?

Also, is this a ranch with a basement or other? And do you have a gas water heater? The depressurization caused by fans in the house and/or attic can backdraft a naturally drafted gas appliance.

Bud
 
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Old 06-22-15, 03:47 AM
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Originally Posted by Bud9051
Tell us what other vents you have besides the two gables, ridge, soffit, or other?

Also, is this a ranch with a basement or other? And do you have a gas water heater? The depressurization caused by fans in the house and/or attic can backdraft a naturally drafted gas appliance.
Yeah, I just learned something new today. First, I did not know what soffit vents are so I have to google it to see the pictures. So, now I understand why the attic has those soffit vents along the side of the wall. And here I am was about to ask and seal those vents to prevent termites from entering.

My house is just a regular two story house with no basement. I have an electric water heater.
 
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Old 06-22-15, 06:25 AM
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So no gas exhaust chimney going up through the roof, water heater or furnace?

Termites would not usually enter through the soffits which for a two story are just above the second floor windows.

I'm not sure if you were just stating an example with the 15' x 20' room or if you are dealing with two concerns, hot house and hot attic. These would be two separate problems. I'll address the attic but can also address the hot room if you need.

Also, remind me as to your climate, all hot or mixed hot and cold.

Attics will get hot, but if they are sealed off and insulated from the house below they should not be a problem. Using fans either inside a house or in an attic will increase the air leakage in through your walls. Humidity, dust, and pollutants like pollen will degrade the building structure over time and reduce the indoor air quality. Although a hot CA climate doesn't have all of the concerns we face here in the northeast, it is still a best practice to ensure your natural ventilation is working properly. To do that we would need more information on your current vents, NFA (net free area) location and height of the attic.

If you are only interested in your fan question, I agree with PJ, one fan should be fine as long as there is another opening for air to enter or exit as needed.

NO I would not use a box fan in an attic. As you said, it wasn't designed for that application and burning down your house is not an option.

Describe your problem/s in more detail so I can stop rambling on.

Bud
 
  #6  
Old 06-22-15, 02:04 PM
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Well, lucky that I asked and you gave me a lesson in this. I was about to do some really stupid weekend warrior stuffs.

Anyway, I went up to the attic just now and removed the extra attic fan. I did notice a little mold around that area.

Climate is only 4 months hot and 4 months cold. The rest is good weather.

Chimney does not go into the attic and the roof is tile. Attic insulated.

Originally Posted by Bud9051
Describe your problem/s in more detail so I can stop rambling on.
Are you rambling? Just kidding. Actually, like I said, the info that you provided has been very educational. All this time, I got the concept wrong and that is to suck all hot air out. Now, I understand that the amount of hot air sucks out also needs the same amount of fresh air back in. It is the same concept of Whole House Fan or cooling down the inside of a PC.

I am good now. Thank You again.
 
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