Q - My children have allergies and my house gets dusty. Are freestanding room-size air cleaners as effective as one mounted in central furnace or air-conditioner blower? Do they use much electricity? K. L.

A - Room air cleaners can be as effective as a furnace blower-mounted air cleaner and are often less expensive. They usually also include a charcoal filter to remove odors. One unit can clean the air in two adjacent rooms. In today's airtight houses, an efficient air cleaner is often necessary.A central furnace air cleaner operates only when the furnace or air conditioner is running. Operating the furnace blower continuously can drive up your electric bill. You can run a room air cleaner continuously and move it to rooms where you have the greatest dust or allergy problem.

Several general types of room air cleaners are available - High Efficiency Particulate Air (HEPA), electrostatic precipitator, pleated media, electret and ionizer. HEPA and electrostatic precipitators are the most effective, especially for extremely small smoke particles.

A HEPA (very dense and finely packed filter material) air cleaner is better than 99% efficient at removing all the particles (dust, smoke, pollen, mold spores, etc.) from the air. These super-high-efficiency HEPA units are often used in hospital operating rooms and industrial "clean room" areas.

HEPA air cleaners are not available for central furnace-mounted units. The very dense filter material would create too much air resistance for the furnace blower to operate efficiently.

Electrostatic precipitators electrically charge dust and pollen particles as they pass through the air cleaner. These charged particles then stick to plates of the opposite charge in the air cleaner. Every month or two, you remove the filter cells and clean them in your dishwasher or bathtub.

Pleated media is a lower efficiency, more-loosely packed type of HEPA. The electret material is similar, but it creates a natural static charge to trap particles. An ionizer charges the air itself to capture dust.

Select a room air cleaner with a high maximum air flow rate. The more room air that flows through it, the quicker and better it cleans. Also consider the weight, which can range from about 12 to 43 pounds. A lighter unit is easier to move from room to room.

The electricity cost to operate a room air cleaner ranges from 40 watts to 200 watts (low continuously fan speed). At an average electric rate of eight cents per kilowatt-hour, it costs about one-half to 11/2 cents per hour.

You can write to me for UTILITY BILLS UPDATE No. 024 showing a buyer's guide of 16 manufacturers of room air cleaners, addresses, types of filtration method, model numbers, maximum air flow, weight, and price. Write to James Dulley, The Deseret News, 6906 Royal Green Drive, Cincinnati, OH 45244. Please include $1 and a self-addressed STAMPED BUSINESS-SIZE envelope.

Q - Would you explain what aerogel insulation is and how it is supposed to reduce the damage to the Earth's ozone layer? H. M.

A - Aerogels are not currently available, but much research is being done. Aerogels are gel materials dried under high pressure and temperature, producing one of the lightest solid materials. A 1-inch-thick piece of aerogel vacuum sealed in plastic has an insulation value of R-20. This is six times better than fiberglass.

The ozone layer is saved because the aerogel can replace standard rigid foam insulation which is often made with chlorofluorocarbons (CFC's).