Dear Jim: We have an airtight, efficient house and we might need some room air cleaners in addition to our furnace air cleaner. Will room air cleaners help allergy and dust problems and which ones are most efficient? – Beth D.

Dear Beth: Although a central furnace-mounted air cleaner certainly helps, using several additional room air cleaners will remove many more particles and allergens from the air. I have an efficient electrostatic furnace air cleaner and I use two smaller ones in my study and bedroom.

If you have allergies, you know it from the symptoms. People without allergies also may suffer health hazards from poor indoor air and not be aware of it. According to the EPA, indoor air quality in an efficient, airtight house may be worse and more hazardous than outdoor air with smog.

Many of the particles that cause allergies (mold, dust mites, pollen, dander, etc.) are relatively large particles. These larger particles puff up when you sit on a sofa, for example, and you breathe them in.

These larger particles settle back down again too quickly to be drawn into the furnace air return, so the central furnace filter does not get a chance to remove them. A properly sized room air cleaner will remove them quickly so the next time you sit on the sofa, fewer particles will puff up.

The two most effective room air cleaners are “true” high efficiency particulate air and electrostatic designs. You will find hundreds of low-quality room units available and many are not effective. Be careful when selecting and avoid ones with words such as “HEPA-like” on the packaging.

A HEPA filter works by forcing the room air through a dense filter media. To be a true HEPA, it must remove 99.97% of all particles down to .3 microns in size. These models require a powerful fan to force the air through the filter, so they use a little more electricity than electrostatic models.

Electrostatic models have plates inside that electrically charge the particles. This makes them stick to collector plates with an opposite charge to remove them from the air. Every month, slip out the collector assembly to rinse off the dust, smoke and allergen particles.

Select a model with several fan speeds, especially if you plan to use it in a bedroom at night. Models with a charcoal after-filter also will remove odors and some volatile chemicals. The heaviest charcoal filters are best.

Clean air delivery rating is a good method to select a room air cleaner. Each model is tested to determine how well it removes smoke, pollen and dust. This rating, often shown on the packaging, helps determine which model is best for a particular room.

Dear Jim: I am considering installing a gas fireplace in my living room. I am not sure whether I should get a vented or a vent-free model. Can you explain the difference between the two types? – Paula W.

Dear Paula: The main difference is a vented model exhausts the flue gases outdoors and a vent-free model exhausts the gases indoors. This is similar to a kitchen gas range which has no vent either.

Most states now approve the use of vent-free gas fireplaces, but check your local codes first. If you are planning to use the fireplace for a continuous source of heat in the room, then a vented model is your best choice.

Write for (instantly download — www.dulley.com) Update Bulletin No. 885 — buyer’s guide of 15 manufacturers of effective room air cleaners listing types, speeds, recommended room sizes, features, prices, CADRs and an allergen size chart. include $3 and a business-size SASE. Send to James Dulley, 6906 Royalgreen Drive., Cincinnati, OH 45244