The Inside Outside Guys: Attic fans: Are they useful?

Ken Calverley and Chuck Breidenstein
Special to The Detroit News

If you lived on the Gulf Coast in the early part of the last century, you were privy to the evolution of different versions of the Swamp Cooler, initially a fan blowing hot air over a tub of ice, to offer relief from the oppressive heat.

Since that time, Americans have continually sought ways to stay cool and dry during the summer months, using everything from a cold compress on the back of the neck to central air-conditioning systems.

A typical solution for many depression era homeowners was to wait until after sunset before opening a few windows on the upper floor for warm air exhaust and a few on the opposite side and lower floors of the house for cooler “make-up” or replacement, air.

One of the systems that came into the market several decades ago was the “whole-house” ceiling mount exhaust fan.

In most cases these behemoths were mounted in the upstairs hall of a typical two-story box colonial.

What you saw from the hall was a metal framework surrounding operable louvers. Above those louvers was a large electric motor connected to a metal fan blade by a belt drive.

With the flip of a switch the motor spun the blade, the louvers opened, and the house rumbled as warm, moist, air from the home was drawn into the attic and, hopefully, exhausted through the attic vents.

If a homeowner strategically opened a few lower windows, cooler and dryer air would be drawn into the home to replace what was being exhausted through the attic.

It sounds like a great concept and, for some who have enjoyed the use of these units for many years, they are a near indispensable appliance.

But there are some considerations to observe for those wanting to install such a device.

To begin, the Guys never suggest “dumping” air from the home into the attic space and hoping it will properly exhaust through passive roof vents.

Additionally, the air we are moving into the attic is moisture laden. Moisture that is not exhausted from the attic can condense on wood surfaces or organic insulation and support the growth of molds.

Our advice always is to provide direct and continuous ductwork from the fan to outside – preferably not a roof penetration — but, instead, a sidewall or eave location away from air intakes and operable windows.

We create a lot of penetrations in our ceilings for such things as lights and fans. Warm air will flow through the gaps and cracks surrounding these penetrations into the attic.

Another item to consider with these units is make-up air. As with any exhaust air device in the home, we should strategically design and install a means for replacing what ever volume of air we are removing.

These fans can move 1,000  cubic feet per minute or more. That is equal to 2.5 times the air volume of a standard three-fixture bathroom! If you do not have a dedicated means of replacing that air, the house will draw it in through gaps and cracks around windows, doors and baseboards.

In some cases, you may hear that intake air “whistling” through such gaps.

One consideration with these units often overlooked is the breach in the ceiling plane of the home.

The Guys believe all conditioned space should be enclosed by airtight walls, floors and ceilings that are well insulated against heat movement.

When we cut that big hole in the ceiling, it becomes a major source of convective air movement from the home into the attic whether the fan is running or not. So, think of mid-February when you are trying so hard to maintain every BTU of heat in the house and you effectively have a hole in your ceiling that runs directly into a cold attic.

Some installers construct a chase in the attic around the unit such that they can wrap it in thermal insulation during the winter months, but unless this is done every seasonal change and done correctly, it is nominally effective.

Our suggestion to any homeowner contemplating installation of such a unit is to put your dollars to a better use by adding to your attic insulation and contacting a company such as  Sharons Heating and Air Conditioning in Westland.

Sharon’s can design and install a system to keep you cool and dry in the summer months without jeopardizing your attic space. And the only thing you must do? Set the thermostat to your personal comfort level and enjoy.

Use your dollars wisely and protect the value of your home by using professionals like those you will find at Insideoutsideguys.com.

For housing advice and more, listen to the Inside Outside Guys every Saturday and Sunday on News/Talk 760, WJR-AM, from 10 a.m. to noon or contact us at insideoutsideguys.com.