Q - Even with our furnace air cleaner, the air in our house gets awfully stale. Would you explain how energy-efficient heat recovery ventilators can bring in fresh outside air without wasting a lot of energy? F.M.

A - Heat recovery ventilators used to be called air-to-air heat exchangers. They can recapture from 50 percent to 70 percent (rated efficiency) of the energy otherwise lost through ventilation and can help control humidity levels. These improve the indoor air quality and reduce your "stale air" feeling.Using various types of heat exchanger designs, the warm outgoing stale air transfers its heat to the incoming fresh air. In the summer, the cold outgoing stale air cools the incoming fresh air. The stale air and the fresh air are kept separate from each other in the unit.

Depending on your needs, you can install either a window or through-the-wall room-size unit, or a whole-house unit. In both types, there are two small fans, one intake and one exhaust, to control the air flow. A wholehouse unit can be installed in an existing house.

In a whole-house unit, the stale air intakes are often located in the bathroom, kitchen and hobby room. The fresh air outlets are often located in a living room, family room, or dining room. They should definitely be located in different rooms than the stale air intakes.

In cold climates, a non-enthalpy type of heat exchanger material is usually recommended. In this type, moisture is not transferred between the outgoing stale air and the incoming fresh air. This helps control the indoor humidity level.

In milder climates, an enthalpy type of heat exchanger material is often preferred. In this type, moisture can transfer between the two air streams. When air-conditioning, the outgoing stale air can draw some of the moisture out of the incoming fresh air before it enters your house.

Most heat recovery ventilators offer several types of controls - timed operation, variable-speed, and humidity-level-controlled. Continuous low-speed operation is often recommended with an automatic speed-up when bathrooms are used, for example.

The typical minimum recommended indoor air ventilation rate is .5 total air changes per hour (ach). You can multiply the floor area of your house by the height of the ceilings to determine the total air volume. Then multiply this by .5 and divide by 60 to get the required cubic feet per min-ute (cfm) capacity of a heat recovery ventilator.

You can write to me for UTILITY BILLS UPDATE No. 080 listing the manufacturers of room-size and whole-house heat recovery ventilators, air flow capacities, types of heat exchanger, and efficiencies. 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 - I want to help reduce the greenhouse effect. About how much carbon dioxide (greenhouse gas) does a person produce? H.K.

A - The majority of the carbon dioxide gas produced is from the burning of fossil fuels to produce energy. On average, each American injects more than 40,000 pounds of carbon dioxide into the air each year.

To run a typical average-efficiency refrigerator for one year, a coal-fired power plant produces more than 2,000 pounds of carbon dioxide. Switching to a new high-efficiency refrigerator can reduce that by about 600 pounds. A general rule of thumb is that for each kilowatt-hour of electricity saved, about 1.5 to 2 pounds of carbon dioxide is prevented from entering the atmosphere.