FILTERS

Best for trapping dust, pollen, and smoke without emitting ozone, an irritant.

But effectiveness varies considerably among models. They typically cost more per year for both electricity and replacement filters. Portable models tend to be noisy at high speeds, and do-it-yourself whole-house furnace filters were fair at best for smoke removal.

How they work A fan pulls air through a filter. Portable models typically use high-efficiency particulate air (HEPA) filters; whole-house units use pleated fabric filters and are attached to forced-air systems.

Price $100 to $800 for portables; $10 to $30 for better DIY whole-house filters; $200 to $500 for whole-house systems (plus $200 or more for installation).

ELECTROSTATIC PRECIPITATORS

Best for low operating costs. Some do a fine job of removing dust, pollen, and smoke.

But all create some ozone, which can aggravate asthma and decrease lung function. Models with small fans or no fans are ineffective at removing dust and smoke. Models with a fan can be noisy at high speeds. Models with plates need more maintenance than filters.

How they work An electrical charge is applied to the particles drawn into the device. Then the particles are captured onto flat plates or filters.

Price $250 to $800 for portables; $400 to $1,150 for professionally installed whole-house models (plus $200 or more for installation).