Changing or cleaning the furnace filter is one of the easiest things you can do to prolong the life of your heating and air conditioning system – and keep it operating efficiently.

Keep in mind that all furnace filters are not created equal – especially if you have allergies, asthma or other respiratory problems.

There are different types of furnace filters:

Disposable fiberglass filters are the least expensive – and also the least effective, designed to block only large dust and dirt particles to protect your furnace. Smaller particles, like pollen and mold, pass right through.

Washable “electrostatic” filters have a static charge that attracts dust, dirt and other matter. These filters are slightly more effective than disposable, but still block only 15 to 20 percent of airborne particles.

Pleated “allergy” filters use a much denser mesh material to trap particles. The pleats increase the surface area, eliminating large allergens like pollen and mold – most are 35 to 50 percent efficient.

If allergies and respiratory problems aren't a concern for your family, a disposable or washable filter can be enough to keep your furnace clean. But it's important to change or clean the filter every month – remember that dust and dirt are the cause of half the repair calls to service technicians!

A pleated filter is a cost-effective option for reducing allergens. These filters cost around $5-$15 each, but are designed to last up to three months. A high-efficiency pleated air filter, shown in the photo at right, costs around $250 to $450. Electronic air cleaners are expensive, ranging from $650 to $850, but they're the best at removing harmful particles and pollutants from the air. In many cases, the initial cost can be offset with lower medical bills.