Electrostatic Air Filters
DEAR TIM: I am tired of using those flimsy disposable fiberglass filters for my furnace. I feel it is bad for the environment. Unfortunately I can't afford an electronic air cleaner. Are there reusable air filters that do a great job of capturing dust? Has technology improved to a point where filters are able to capture and trap carbon monoxide? What should I look for when purchasing a reusable air filter? John R., Shelbyville, IN
DEAR JOHN: I share your feelings about those inexpensive fiberglass filters. My dislike grew even more once I found out that those filters are designed only to protect the furnace and air conditioning components. They are virtually useless in capturing visible and invisible dust and pollen particles.
Residential air filters are not made equal - not by a long shot. Different styles and types trap different sized particles. For example, the expensive built-in air filters that are connected to 120 volt household current do a swell job of grabbing very small particles like smoke. However, because of their internal design, larger sized particles can sometimes pass through these filters and become heavily charge with electricity. Once the particle leaves the duct work, it is immediately attracted to any object that has an opposite electrical charge. You can often see evidence of this when you see dust and dirt trails around supply duct registers.
Did you know you actually may be able to afford an electrostatic air filter? You can purchase very slick tribo-electrostatic reusable filters that slide right into the same slot that you place your existing disposable filter. They cost just a fraction of what you would pay for a built-in electronic filter setup. The photo to the right shows two different filters. The one on the left has a built-in carbon monoxide detector.
These washable filters are made from a variety of plastic and paper filter media that have their own built-in electricity. When air passes through the filters, the electrical charges increase dramatically and allow the filters to grab very small invisible particles that are floating in the air. Some of the pleated paper electrostatic filters are not washable. Once dirty, you are expected to throw them away.
You need to pay attention when you purchase one of these reusable filters. Furnaces and air conditioners are designed to handle a certain amount of resistance within the duct work system. Many furnace manufacturers do not want the overall resistance within the system to exceed .5 inch water column resistance. In many houses the duct work and the supply and return register grilles create approximately .2 inch resistance without any filter in place. Since the filter creates more resistance to air flow as it picks up and retains dirt and dust, you want to purchase a filter that has the least amount of initial resistance. Initial resistance is the resistance to air flow the filter creates when it is perfectly clean. You can purchase some electrostatic filters that have a low initial resistance of just .08 inch!
If you suffer from certain allergies, it is also possible to purchase these reusable filters with anti- bacterial protection. The anti-bacterial compounds are actually part of the plastics that are used to build the filter media. When you wash the filters on a regular basis, you do little to diminish the anti-bacterial protection. Tests have shown that the filters retain their ability to inhibit the growth of the bacteria, mildew and mold for up to ten years.
Technology has advanced a great deal with respect to electrostatic filters, but not as far as you would like. Although no electrostatic filter can trap carbon monoxide, you can buy certain filters that have a built-in carbon monoxide detector. Most furnace and air conditioning systems are designed so that all of the air in your house is transported through the filter every 15 minutes. This means a filter with a built-in detector can act as a fantastic early warning system in the event a furnace, hot water heater, or other appliance begins to emit poisonous carbon monoxide. The detectors in these filters have special sensors that minimize false alarms. In the event of real danger, these detectors sound an alarm that passes right through the duct work and alerts inhabitants in each room of the house.
The filters that have the carbon monoxide detectors are also equipped with a very handy feature that will save you money. They have a built-in electronic cleaning reminder tone that issues a friendly signal telling you it is time to clean the filter. If you choose to ignore the tone, the filter becomes more persistent and chirps at more frequent intervals. It works to your advantage to clean the filter as soon as possible. Clean filters allow your heating and cooling equipment to operate at peak efficiencies which lowers your utility bills!