Clearing the Air

Whole-house filters, like the extended media filter shown here, must be professionally installed in return-air ductwork.

Flat Filters: change forced-air furnace filters once a month

Extended Media Filters: These 8-inch-thick filters require a pro to plumb them into the ductwork.

Electronic Filters: These work paticularly well on smoke particles and never need replacing, though they must be scrubbed every few months.

Ultraviolet Filters zap airborne bacteria and viruses

Portable Room Air Filters: These work well in houses with no central air or heating

HEPA Filter