Will attic fan attack heat buildup?

Q: I have extreme heat buildup in my attic and am considering an attic fan. The house faces south, with trees on the west and east. The house stays warm at night even when the temperature drops several degrees. The attached garage is the only part that stays in direct sun the whole day. Would an attic fan be a good investment?

A: I presume you have adequate insulation, and both upper and lower attic vents for good convective flow. Given that, an attic fan may be beneficial.

For those not aware, there are a few variations of fans that perform different functions: The type most of us are familiar with is the conventional attic fan that sucks air in through the multiple attic vent openings, pushing hot air directly to the exterior. These come in many sizes, are electrically or solar-powered, controlled via a manual switch, thermostat or humidistat, and can be mounted on the pitch of the roof or on a gable end.

When choosing a fan, people mistakenly believe bigger is better. But the limited (and sometimes blocked) vent openings in a typical attic are easily overwhelmed by many of the larger fans, forcing air to come from areas not intended, such as the duct system or from inside the house, where air may already be cool. Much recent literature concludes an attic fan is generally not desirable in an air-conditioned home.

The second fan type is a whole-house fan, sometimes called a "Southern fan." These huge fans, some as big as four feet square, are mounted into the ceiling beneath an attic. Giant spring-loaded weather-stripped louvers keep heat from escaping into the attic in winter. Fire up the motor, and the louvers are forced open.

Crank it up to a high-speed setting and seemingly every air molecule within the zip code is sucked up through a propeller that just might have been salvaged from a B-29. Close the fireplace damper, open the front door and anchor your small children securely, cause this bad boy is going to move some air and cool down the house right now.

The mass of air is forced up into the attic and out wherever the heck it can go. And that will be anywhere and everywhere. They blow a lot of insulation around, so the higher the roof pitch, the less mess it will make initially.

Not to create confusion, but newer homes also have what are called whole-house fans. These code-mandated units are generally not much more than glorified bathroom fans, ducted through the attic to the outside. They are made for bringing fresh air into the house over time, not cooling the house and attic via hurricane-force winds.

I am hoping for feedback from readers on this one: Attic ridge vents make a lot of sense logically and have become very popular in recent years. Code authorities have been so impressed that they allow one to get away with only half as much attic venting when ridge vents are installed, because of their efficiency.

But with variables such as orientation to the sun, trees, roof pitch, installation technique, insulation, roof type and color taken into consideration, I find that the hottest attics are the ones with these ridge vents installed. The old-style mushroom vents, turbine vents, and even completely unvented attics in older houses seem to be cooler.

Tell me: After adding ridge vents, did you notice a change in the heat buildup in your attic? I will share some of your comments in a future column.

Q: I've heard warnings about the risks involved in moving insulation that contains asbestos. But what about old cellulose or rock-wool types?

I need to remove large quantities of both from my attic. Just touching this stuff creates clouds of fine dust. If I remove it myself, I am sure that a great deal of this particulate matter will end up in and around the house.

A: While there is growing controversy on such removal issues, particularly about fiberglass insulation, there are presently no requirements for insulation installers to wear protective breathing equipment, respirators or even dust masks. But certainly all types of insulation are potential irritants, as well as the dust covering it in the attic.

Use a NIOSH certified (N95 or greater) dust mask, or preferably a respirator with HEPA protection. Yes, some of the insulation may end up in the house when you pull it out. You may want to protect vulnerable areas with plastic sheeting, sweep and mop the affected areas, then air the house out thoroughly afterward.

Also consider that many insulation contractors have equipment geared specifically for sucking up old insulation.

Darrell Hay answers readers' questions. Call 206-464-8514 to record your question, or e-mail dhay@seattletimes.com. Sorry, no personal replies. More columns and a message board at www.seattletimes.com/columnists.