Hidden Energy Guzzlers: Making sure your attic is well-ventilated

Uncategorized May 23, 2013 1 Comment

When was the last time you stuck your head up in your attic to check the temperature? I posed that question to a group of men I meet with weekly, and the answer was, “Never.” If you’re like me, you don’t think about what’s going on in your attic as long as you think you’ve got enough insulation. Out of sight, out of mind. But what you don’t see can be hurting you.
Ventilation of the home attic is important for two reasons.
• During the summer, excess heat that builds up in the attic during the day results in high energy costs for cooling.
• Also, moisture produced within the home may move into the attic if ceiling vapor barriers are not used. If this moisture is not exhausted from the attic it can condense and cause insulation and construction materials to deteriorate. Thus, temperature and moisture control are the major reasons for providing attic ventilation.
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. Making sure we have the best insulation is one part of the solution, and making sure our attic is properly ventilated is the other part. So…how do we actually ventilate an attic?
Attic ventilation can be accomplished by gravity ventilators, wind assisted ventilators or through electric or solar powered ventilators. Regardless of the method used, the purpose is to provide uniform ventilation of the attic for proper temperature and moisture control. There needs to be air movement in the attic in both summer and winter months.
At first it may seem odd to add insulation for warmth and then purposely allow cold air to enter the attic through vents, but this combination is the key to a durable and energy-efficient home. Here’s why: in the winter, allowing a natural flow of outdoor air to ventilate the attic helps keep it cold, which reduces the potential for ice damming (snow that melts off a roof from an attic that is too warm and then re-freezes at the gutters, causing an ice dam that can damage the roof). Proper insulation and air sealing also keeps attics cold in winter by blocking the entry of heat and moist air from below. In the summer, natural air flow in a well-vented attic moves super-heated air out of the attic, protecting roof shingles and removing moisture. The insulation will resist heat transfer into the house.
Natural ventilation is the most common way that homes have of achieving attic temperature and moisture control. This method takes advantage of two principles:
• First, as air is heated it becomes less dense and rises.
• Second, wind movement over and around a home creates areas of high and low pressure, which tends to move air.
Ventilation caused by wind pressure differences requires less vent area to achieve the same ventilation rate as ventilation by gravity. One problem with wind ventilation is that the areas of high and low pressure change with wind direction, causing difficulty in locating inlets and outlets so that ventilation will take place regardless of wind direction.
Attic Fan Ventilation is intended to cool hot attics by drawing in cooler outside air from attic vents (soffit and gable) and pushing hot air to the outside. NOTE: If your attic has blocked soffit vents and is not well-sealed from the rest of the house, attic fans will suck cool conditioned air up out of the house and into the attic. This will use more energy and make your air conditioner work harder, which will increase your summer utility bill. You don’t want your unfinished attic cooled by your air conditioner.
So, which is better? Natural ventilation is the least efficient way to ventilate your attic because it depends upon air pressure changes heavily affected by wind direction. Attic fans keep a consistent movement of air going, regardless of wind direction. Don’t want to spend money on electricity to keep those fans running? No problem. Recent advances in technology have made it possible to install efficient attic fans that are solar powered. That means your fan will be running without using a single watt of electricity. Think about it. If your attic is 50 degrees cooler, your air conditioner will not work as hard and there may be many days when you won’t need it on at all.

One Response to “Hidden Energy Guzzlers: Making sure your attic is well-ventilated”

  1. tent air conditioner says:

    I found a similar post to this one on a different blog, having said that I enjoy your take on it a whole lot better. Thanks for the added perspective.

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