What should attic temp be?

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You need soffit vents to provide a source of air to replace that exiting from the ridge vent.

Soffit vents by themselves, without a ridge vent, probably won't do much.
 
When I lived in NJ, I lived in a relatively small (1400 sq ft) home. I installed an attic fan sized for a home twice that size, with a variable speed control. Opening the attic door, I used it as a whole house fan, primarily at night when temperatures were cooler.

While it cooled the house down, it did nothing for humidity. Obviously, airborne pollen and other stuff came in the house too.

I finally went to central air.
 
Good points I had not considered with my attic situation. I do have ridge vents and two roof vents. As with some others, I always crack my attic door, which is in the garage, and then turn on a fan sitting in the garage aimed at the attic door. Temperature will drop to about 5 degrees above ambient temperature in about two hours. Now, I only fire this "system" up when I get home around 1700. I have a programmable thermostat in the house the cranks down to 73 degrees around 1600. I know it makes a difference come early evening when the house reached 73 degrees, say around 1830 or so. But, one day I was home and it was hot as all get out, opened the attic door and did the same thing as I always do in the evenings, but it really didn't make a difference. Temperature stayed about 115 up until the sun was not directly overhead. I've always wondered how much thermodynamics played into this. Once the attic reaches it's highest point and the whole attic is a heat sink, does dropping the air temperature really drop the temperatures of the substrate that much? Heat always travels from hot to cold. I got a boat load of insulation up there also. But heat transfers easily. It's funny. In the mornings I check the temperature. It will be a lot cooler than the ambient temperature up until about 1000, about the time the sun starts hitting the shingles directly overhead so I know the ventilation up there is pretty good. Hence, my dilema on putting an attic fan up there.
 
i have an attic fan installed on the side of the roof next to the top ridge. it has gravity held flappers which close when the fan turns off to keep bugs and rain out. it is thermostatically controlled to turn on at 90F and off at 90F. it usually turns on around 10am and turns off around 6pm.
i also have a big grate installed in the attic way on the other side, so the fan sucks air through the grate, draws it across the entire attic and expels it out the flappers.

before i install the attic fan and the grate my atytic had those whirlygigs on the roof and the temp would be 30-40 degrees hotter in the attic than outside in the shade. now that the fan is installed and working it only gets to be around 10 degrees hotter than outside temp in the shade.
thats 20-30 degrees difference. even though the fan cost $50 and around $5 each month to run, it save me about $25 a month on electric bill becuase my a/c runs less.
 
Schmoe, what was the ambient when your attic reaches 115F?

ACiD, do you have any current passive ventalation (soffits, gamble, ridge, etc) sans whirlywigs.
 
no i got rid of all passive ventilation whirlygigs and all. made the roof look alot better. there is only the 1 single fan on one side of the attic, and a large grate on the other side.

it is my belief that when you go to active ventilation you should close up all the passive stuff because air awalys travels through the path of least resistance. you want the air to travel through the entire attic, not just one part of it. if you have a fan on one side of the attic and some vents in the middle, the air will just go from the middle vents to the fan and totally skip 1 whole side of the attic.
 
My home that I am building will contain continuous soffitt venting as well as ridge vents. Heat rises so you need continuous venting at soffitts to allow ridge vent to work effectively. I am using Cobra 2 vent at ridge and traditional 1x6 times 2 with 4 inch screen in center of soffitt. If you add power venting to to system like that you risk reversing what you are trying to achieve which is energy consumption. You will have the cost of power to generate the fan and you will also add a level of suction in the attic space that will draw conditioned air from within the dwelling into the attic space. This will increase the load on your HVAC system to maintain what is lost through the roof from ceiling, etc..

Air movement in attics need to be enough to to prevent buildup of moisture as well as heat, but not to much that it starts to effect the inside of the home.
 
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