Configuring Attic Ventilation Based On Outside Temperture

Be it winter or summer the goal is to keep the ventilated attic as close as possible to the outside temperature.

Configuring attic ventilation based on outside temperture.

If your attic soars above 100 degrees and reaches the 150 mark its time to consult professionals. But in the winter the amount of water vapor that the air can hold is substantially lower. Attic fans draw cooler outside air into the hot attic area through attic vents located either on the roof or on the wall near the gable to reduce the space s temperature. Providing half air change per minute will lower the temperature to about 106 degrees f.

Roof shingle temperatures will be higher during no wind conditions leading to a higher heat load on the attic. Calculations indicate that on a july day in texas a ventilation rate of one air change per minute for a typical attic using 95 degree f air will lower the peak attic temperature to about 101 degrees f. This design is less efficient when hvac equipment and ductwork is in the attic space. Then stack effect is the prime air mover driven by the attic to outside air temperature difference.

As figure 1 demonstrates if the outside air is 32 c 90 f and 70 percent rh it is drier than interior attic space which is 43 c 110 f at 40 percent or higher rh. In the summer time a well ventilated attic helps to keep the attic cooler. A well ventilated attic helps to avoid problems with moisture and heat buildup. Attic temperature depends on the amount of solar radiation construction details and the rate of ventilation.

Therefore the greatest need for attic ventilation is when there is little wind pressure to force air in and out of the attic. In these instances systems have a harder time maintaining the desired temperature. Attic ventilation works on the principle that heated air naturally rises primarily utilizing two types of vents. The fire started on an outside wall went up the wall and into the attic space spread across the entire house in the attic with no smoke coming into the house until the ceiling was about to collapse which was far too late.

Ideal attic temperatures shouldn t be more than 10 to 20 degrees hotter than outside temperatures. Luckily my wife and i were upstairs and hear the rafters crackling looked outside and saw the wall of fire and got our. So my house burned down a couple of years ago.