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Old 06-17-2010, 10:59 AM   #16
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1971 Mansard Attic Ventilation Nonexistent


This link, if it will open, will tell you how many BTUs are giving you your 82F
http://en.wikipedia.org/wiki/R-value_(insulation)
You need to know your attic temp and the sq. ft. of the ceilings of the rooms that interface with the attic temp.

Knowing your attic temp, with this link you can figure the effectiveness and cost for various methods, including adding an AC.

The attic temp would have no effect on the room temp if
both were at the same temp or
the room ceilings were perfectly insulated.

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Old 06-17-2010, 11:29 AM   #17
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1971 Mansard Attic Ventilation Nonexistent


Really like the idea of the radiant barrier and adding the insulation. Still does't resolve my lack of ventilation.

I am thinking I can lower my static vents (4) on the roof and then replace two of the static vents with attic fans or Whirlybird turbines, and cover the other two.
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Old 06-17-2010, 03:28 PM   #18
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1971 Mansard Attic Ventilation Nonexistent


"
How much attic ventilation is required to provide proper temperature and moisture control? A number of studies sponsored by federal energy funds are under way to look at ventilation rates and methods. However, several studies previously made can help with this decision. The maximum ventilation rate is required to remove heat during the summer cooling months. Attics can reach temperatures of 150 to 160 degrees F during a summer day, although outside air temperatures are only 95 to 97 degrees F. The cooling load for a home air conditioner depends on the difference in temperature between the inside and outside air, and reduction of attic temperatures from 155 degrees to 105 degrees F will result in a significant reduction in cooling load. In a home with poor ceiling insulation, heat movement through ceilings may account for 30 percent or more of the total cooling cost. With a well-insulated ceiling, this source of heat may account for only 12 to 15 percent of the total cooling cost. Thus, high attic ventilation rates are most important for poorly insulated ceilings. A poorly insulated ceiling is one whose R rating is less than 14 or one with fewer than 4 inches of fiberglass, rockwool or cellulose insulation.

. . .on a July day in Texas, a ventilation rate of one air change per minute [60 per hour?] for a typical attic using 95-degree F air will lower the peak attic temperature to about 101 degrees F. Providing half air change per minute will lower the temperature to about 106 degrees F. Thus, the first half change per minute is most effective and a doubling of this rate only achieves about 5 degrees F additional cooling. Studies indicate that further increases in ventilation are not effective in significantly reducing attic temperatures."

Last edited by Yoyizit; 06-17-2010 at 03:33 PM.
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Old 06-18-2010, 07:18 AM   #19
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1971 Mansard Attic Ventilation Nonexistent


I'd do what Ed said and install continuous ridge vent. You can also put a box fan or any type of house fan on a timer in your attic and let it push air up thru vents. This is what I've done in my attic, as it is quieter than a big, roof-mounted exhaust fan. Also easier to replace once it dies. Good luck!

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