Whole-house fans and attic fans: Two different approaches to cooling

Q. Tim, what can you tell me about whole-house fans and attic fans? Do they really work to cool an attic space? I’m not sure which one I should consider one since I have air conditioning. What’s required to allow them to work at peak efficiency? –Robert T., Rockdale, Illinois

A. I’ve installed quite a few whole-house and attic fans and witnessed how effective they can be. Whole-house fans can be found inside a home usually in a second-floor ceiling.

A whole-house fan is designed to pull air in through open windows and doors and exhaust this air through an attic space to the great outdoors. Some can move almost 300,000 cubic feet of air per hour through your home.

The fans can move so much air that if you have the windows open in just one room, it will blow papers off of tables. You can imagine how that would cool you down with that much air blowing across your body. If you’re running an air conditioner, you wouldn’t want to have a whole-house fan blowing that cooled air into your attic.

These fans were the cooling method of choice before modern air conditioning became widespread and affordable. They work well in climates that have lower humidity levels as the nighttime temperature can drop enough that you’d need a blanket on you to sleep.

Attic fans are quite different. They’re installed up on a roof or through an exterior wall up in an attic. A normal-sized one might only move 72,000 CFH of air through an attic. You can get ones that move up to 360,000 CFH of air, but these are usually designed to be wall-mounted.

The attic fans just pull air through a hot attic space in an effort to reduce the infrared heat gain you feel through the ceiling of your home. If you want your home air conditioner to cool you better, then you might want one or two attic fans.

The moving air tries to cool down all the wood attic framing as without the fan the temperature of the entire roof assembly and attic lumber can soar to 160 F or more. Think of your entire roof assembly as a giant glowing ember trying to fry you like a marshmallow over a campfire.

For both fans to work well, they need large exhaust openings in the roof for the moving air to exit. Whole-house fans need windows and doors open and attic fans need lots of soffit vents to suck cooler outdoor air up into the hot attic. Without this open space, the fans will not move much air. It’s easy to install waterproof gable end vents or pot vents in the roof for the air to pass back outside.

I have whole-house and attic fan tips and videos at http://go.askthebuilder.com/fans

Q. Looking for some fast advice about patching blacktop. Does the cold blacktop in bags really work? I’ve got time and energy but not lots of money. – Susie P., Riverside, California

A. The good news is the blacktop patching material sold in bags and buckets really does work. It doesn’t produce the same satin-smooth surface as hot patch asphalt because the cold material usually doesn’t have much sand in it.

If you want success using the blacktop sold at home centers and hardware stores, first start by reading the label instructions. Too many people skip this important step.

I’ve achieved the best results by using a cold chisel and a 4-pound hammer to chisel the edges of the potholes I fill. I want the edges of the patch to be at least 1 inch deep and I do my best to tilt the chisel so the bottom of the hole is wider than the top. This is how dentists keep a filling in your tooth.

It’s very important to remove loose material at the bottom of the pothole. If you have crushed stone with fine particles, add some to the hole and compact it well. Blow all dust out of the hole and brush the edges of the hole so the asphalt will stick well to the sides of the existing blacktop.

I’ve got detailed step-by-step tips and videos showing you tips for patching blacktop at my website, http://go.askthebuilder.com/ blacktop