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Cleaning The Air

Although we use several room air cleaners, my family still has allergies. We are considering a central air cleaner for our heat pump instead. What is the most effective and efficient design?—Judy T.

A central air cleaner is probably a good idea, but don’t totally discontinue using a room cleaner or two. A combination of a room air cleaner and a central furnace/air-conditioner cleaner is a good defense against allergies. Poor indoor air quality, which is often more polluted than outdoor air, can also cause colds and aggravate health problems such as asthma.

Some room air cleaners have fairly powerful motors. Running several of these continuously will consume quite a bit of electricity. Most central air cleaners use a small amount of electricity or none at all.

A high-quality central air cleaner will also keep the heat exchanger and coil surfaces cleaner to maintain efficiency. The effectiveness of air cleaners is often compared by their dust-arrestment ratings.

Also consider the type of particle (allergen) you need to remove from the air. Mold spores, dust mite feces, and pollen are relatively large particles that are easier for many filter materials to remove.

Tobacco and fireplace smoke, bacteria, and viruses are very small particles that require different types of filtration. Check with your doctor or allergist, or have your house air analyzed to determine what types of particles you need to clean from the air. It’s also worth noting that keeping ducts clean and sealed will reduce or eliminate mold and bacterial growth.

Another consideration is the resistance the air cleaner creates in the duct system. A thick, densely packed filter may catch almost all the airborne particles, but it can cause excessive airflow resistance, making your furnace/air conditioner operate inefficiently and increase your utility bills.

To avoid excessive airflow resistance and still have good filtration, several designs of bypass HEPA air cleaners are available with their own blowers. HEPA filter media is often used in hospital operating rooms and is probably the most effective filtration method for large and small particles.

These models have powerful blowers, but they only operate when the furnace runs.

If you have an airtight house that gets stuffy, select a HEPA model that introduces filtered outdoor air into your ducts. A lack of fresh air is often as much of a problem as dirty indoor air. In extremely hot or cold climates, choose a model with a heat recovery unit to save energy.

The most common types of in-line (using a furnace blower) air cleaners are electronic, self-charging electrostatic, and pleated media. Electronic air cleaners use very little electricity. They are particularly effective for removing the smallest particles. Most models will have to be professionally installed and require ductwork modifications.

With an electronic air cleaner, it is important to regularly clean the filter cells to maintain their efficiency and to minimize the production of ozone gas. The cells are generally small enough to fit into your dishwasher for easy cleaning.

Most washable self-charging electrostatic air cleaners slip into the existing filter slot in your furnace. These are very effective for removing larger particles from the air. Each month, remove it from its slot and spray it off outdoors with a hose or rinse it off in the bathtub.

Pleated media filters are dense filters and are also very effective for removing larger particles. Some thick ones require duct modifications. To purify air in addition to cleaning it, install an ultraviolet (UV) light purifier in the return duct. The UV light kills virus, bacteria, mold spore, and other germs.

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