Solar Attic Fan
United States of America (Press Release) July 25, 2008 -- Newburgh, NY July 24, 2008 - Solar attic fans are a great "green" solution for ventilating hot attics on sunny days. But manufacturers typically provide ratings that vastly overestimate the amount of attic space they can effectively ventilate. That can result in installing much fewer fans than you really need to properly vent your attic according to building code regulations.
Building codes divide ventilators into two categories: (1) A/C powered electric fans, and (2) everything else. Wind powered, solar powered, and passive vents are all lumped together in the second category. Why the apparent over-simplification?
The answer is: consistent performance. A certain amount of minimum air flow must be present at all times to ensure proper ventilation. This is codified in the "1 to 300" rule, which means that for every 300 square feet of attic floor space, there must be 1 foot of passive ventilator "free air" space (measured by the inner diameter of the vent itself). This rule establishes a specific relation of size of attic to size and quantity of vents.
source: FPR
Ventilation is rated by how much CFM (cubic feet of air per minute) they move. The problem is, the performance of solar fans is dependent on many variables: season, location latitude, weather conditions, dirt on the panel, angle to the sun, among others. The manufacturers rate these fans when all these factors are at optimum levels, which may actually be only for a few hours a day, and not on all days. But ventilation must be constant, all the time.
So what happens? Even construction professionals often make the mistake of trusting those "optimized" ratings to determine how many vents to install for a given area. Therefore, they assume that the vents are moving much more air than they actually are throughout the day, and end up specifying fewer vents than are required for even minimum ventilation. This violates the "1 to 300" rule, and results in overheated attics in the summer, ice damming in the winter, and moisture-laden attics in the other two seasons.
This analysis shows that we should be highly skeptical of ratings provided by the solar fan manufacturers, and use them for comparison only. When it comes to determining how many vents your attic requires, always rely on the "1 to 300" rule to ensure that your attic is being vented properly, every day, all day long.
Source: www.free-press-release.com
Solar Attic Fan
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United States of America (Press Release) July 25, 2008 -- Newburgh, NY July 24, 2008 - Solar attic fans are a great "green" solution for ventilating hot attics on sunny days. But manufacturers typically provide ratings that vastly overestimate the amount of attic space they can effectively ventilate. That can result in installing much fewer fans than you really need to properly vent your attic according to building code regulations.
Building codes divide ventilators into two categories: (1) A/C powered electric fans, and (2) everything else. Wind powered, solar powered, and passive vents are all lumped together in the second category. Why the apparent over-simplification?
The answer is: consistent performance. A certain amount of minimum air flow must be present at all times to ensure proper ventilation. This is codified in the "1 to 300" rule, which means that for every 300 square feet of attic floor space, there must be 1 foot of passive ventilator "free air" space (measured by the inner diameter of the vent itself). This rule establishes a specific relation of size of attic to size and quantity of vents.
source: FPR
Ventilation is rated by how much CFM (cubic feet of air per minute) they move. The problem is, the performance of solar fans is dependent on many variables: season, location latitude, weather conditions, dirt on the panel, angle to the sun, among others. The manufacturers rate these fans when all these factors are at optimum levels, which may actually be only for a few hours a day, and not on all days. But ventilation must be constant, all the time.
So what happens? Even construction professionals often make the mistake of trusting those "optimized" ratings to determine how many vents to install for a given area. Therefore, they assume that the vents are moving much more air than they actually are throughout the day, and end up specifying fewer vents than are required for even minimum ventilation. This violates the "1 to 300" rule, and results in overheated attics in the summer, ice damming in the winter, and moisture-laden attics in the other two seasons.
This analysis shows that we should be highly skeptical of ratings provided by the solar fan manufacturers, and use them for comparison only. When it comes to determining how many vents your attic requires, always rely on the "1 to 300" rule to ensure that your attic is being vented properly, every day, all day long.
Source: www.free-press-release.com
Solar Attic Fan
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