One of the reasons attic fans are inefficient is that they rely on existing attic vents (in ceilings, ridges, or pediments) to recover the air they expel. Usually, these attic vents are not designed for this purpose and may not be able to supply enough replacement air. How can that be, you ask? Aren't you supposed to take that scorching air out of the attic and send it outside, replacing it with much colder outside air that enters through the roof and the gable vents? In marketing theory, yes. However, construction science yields a different result.
To explain my concern To explain my concern in more detail, arguments A, B, and C were all that was mentioned in the original article. It is not insignificant to hypothesize an idea that overrides these arguments. Innovation comes from understanding the lines of logic and verifying if they are really perfect. Before, I was hoping that we could discuss these issues in some depth instead of just advocating for a conclusion.
We also agree that if the outside temperature is lower than the temperature of the attic (26%), there are openings near the top and bottom of the roof, cooler air will naturally enter through the bottom and replace the warmer air that comes out through the top. All the objections to paved pavements seem to stem from a very limited set of assumptions: leaking roofs, inadequate ventilation ducts in attics, humid climates, etc. No, Caroline, the science is clearlyNo, science clearly says that your house isn't hotter if there's no electrical ventilation on the roof. By the way, yes, my house has sufficient roof insulation, at least in the opinion of several builders and HVAC people.
Two summers ago I installed a ceiling fan (1200 cfm) and immediately noticed that the temperature upstairs was 3 to 4 degrees lower. Fans and electricity bills cost much less than a new roof; you simply have to always consider the bigger picture of the airflow and adjust it for every change. Oh yes, electric attic fans will probably keep the attic cooler, and that means there will be less heat transfer by conduction through the roof. Well, I have returned to the houses to check them every five years and those who use their fans are usually 25 or 30 years old.
For example, if you have an attic that not only has no ventilation, but has insulation in the roof line, the temperature of the shingles will be as high as possible because the flow of conductive heat into the attic is minimized. Some of the frequently cited references are decades old and most have extremely small sample sizes and focus on humid southern climates and homes with problems such as leaking roofs and inadequate ventilation in the attic, causing significant negative pressure. If you want to know the essential facts of attic research, you can download this article (pdf) from the Florida Solar Energy Center, which analyzes research not only on attic ventilation, but also on attics sealed with insulation on the roof line instead of on the flat roof. The problem is that solar energy, ceiling fans, refrigerator, coffee maker, kitchen, cleaning, shower, people, pets, lighting, televisions...
they all use energy, they generate heat, which rises and cannot go out. Your plan will likely require a completely sealed roof, a very thick insulating layer, radiant barriers (layers of reflective foil) above the insulation (preferably between the beams) to block radiation and isolate the hot attic from the cold room, additional ventilation openings, and possibly an electric attic fan to remove hot air from the attic at the appropriate exchange rate. Without electrical ventilation, the attic is naturally, but slowly, ventilated by cooler air that enters through the vents of the eaves and exits through the upper vents of the roof.
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