Q&A / 

High Efficiency Air Filters

DEAR TIM: My air conditioning system didn't work when I turned it on for the first time this season. After spending $60 on a service call, I found out that a huge block of ice had formed inside my furnace. The service woman said my coil was dirty. That doesn't make sense. Seems to me, the air would be much cooler if it was blowing over a block of ice. What happened? Can it be prevented in the future? I'm hot about this problem! R. A.

DEAR R. A.: Cool down, take a break! Once that ice melted and the coil was cleaned, I'll bet you were in good shape. However, you possibly caused the problem by not changing your furnace's air filter on a regular basis.

There is a coil inside your furnace through which air blows. This coil has lots of thin fins. Attached to these fins is a small continuous tube which contains refrigerant. This refrigerant begins to boil inside the tube as the warm or hot air from your house passes over the coil. Prior to boiling, the refrigerant was very cold and as the heat from the air is transferred to the refrigerant the air temperature drops.

When you turn your air conditioner on, the main blower in your furnace begins to recirculate the air through your house. The moist, humid air passes over the cold fins of the coil. The water in the air condenses on the fins just like on a cold glass of iced tea on your patio table. Everything works fine if enough warm moist air can pass over the fins fast enough. If not, the temperature of the fins can drop below 32 degrees F. Ice starts to form on the fins and soon your coil is a solid block of ice.

In your case, the air passageways between the fins became blocked by dirt. This dirt slowed down the air trying to get through the coil. A clogged air filter in your furnace can also slow down the air passing through the coil.

You can prevent this problem by considering the use of higher efficiency air filters. Standard inexpensive spun glass filters are almost always less than 20 percent efficient. Some of them may only be 6-8 percent efficient. These filters are designed to protect your heating and air conditioning equipment, not cleanse the air.

You can purchase air filters that will not only protect your equipment, but also do a remarkable job of cleaning your interior air. These filters can trap very small particles of dust, pollen, mold, and other irritants. Some of these filters work much like the air and oil filters in your car. They are made using pleated filter paper. Other filters are made with fine synthetic polyester fibers. Higher efficiency air filters can sometimes be coated with chemicals that can kill tiny microbes such as bacteria and mold.

There are several advantages to using these higher efficiency air filters. Not only will your heating and cooling equipment perform better, your operating costs may well be lower. The air you breathe will be cleaner, as will your furniture and drapes. That $60 service call could have bought 10 filters that may have lasted through five cooling seasons!


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