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Air Filters


July 10, 2009
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I suffer from severe allergies and asthma. Is there anything I can do to make certain that the air is as free of dirt as possible?

Sure and here's a list:
  • Keep the furnace blower operating in the on position. Even though the space is not being heated or cooled, the air will continued to be filtered.

  • Keep your air filters clean. Although the filter manufacturer may recommend replacing the air filters every 30days, you should replace them more frequently.

  • Invest in an electrostatic filter. This type of filter is charged to attract dust and particulate matter to its surface.

  • Invest in an electronic air cleaner. Electronic air cleaners are multistage filtration systems that are designed to capture a greater percentage of smaller particulates that are present in the air. They install in there turn-air duct and contain a prefilter, a charging section, a collection section, and a charcoal filter. The prefilter captures larger particulates. The charging section transfers an electric charge to the particulates as they pass through. These particles then adhere to the collection plates, which have a charge opposite to that given to the dust and dirt. The charcoal filter helps remove odors and gases that are present in the air.

  • When the highest degree of filtration is needed, use a HEPA (High-Efficiency Particulate Arrestor) filter. These filters are expensive, but they capture 99.97%of the particulates that are 0.3 microns in size. The average dust particle is30 microns in size. A human hair is about 80 microns wide.A true HEPA filter will cost at least $100.00.

  • If mold is an issue,install an ultraviolet light. UV light systems destroy and/or disable microbes that have negative effects on the air quality in buildings.They reduce the growth of mold in air-conditioning duct systems. These systems are especially good to use near the cooling coil of an air-conditioning system because moisture is a component needed to stimulate mold growth.

Where is my air filter located?

Probably right at the furnace, or behind the face of a filter-backed grill. If you are able to locate a large grill in the ceiling or wall of a bedroom hallway, you have probably also located your filters. If the grill has plastic clips or metal latches, chances are that the filter is there. Carefully open the latches and you should see the filter waiting for you. But if there is no filter in the grill, don’t despair. The filter may be near furnace. Inspect the return duct (the duct near the bottom of the furnace) and look for a rectangular slot that's cut into the duct section and close to the furnace. You should see the cardboard edge of the filter. If not, look for a rectangular piece of sheet metal, about three inches wide, and screwed into the turn duct. The piece of metal should extend the entire length of the duct. Removing these screws and the piece of sheet metal should reveal your filter. But be careful; the edges of the sheet-metal-filter slot covers are very sharp.
There is no air filter on my system, or maybe I just can’t find it. What do I do?
If you have looked and still cannot find your air filter, it’s time to call a professional. Chances are that, if you have a filter-backed grill or a filter slot on the return duct, and there is no filter in place, your system is in need of a major cleaning. The purpose of the filter is to keep your appliance clean and operating properly. If there is no filter, there is probably a lot of dirt inside the whole system,including the air-distribution ducts.

How do I know what size filter I need?

The common answer is to replace the old one with one of the same size, and that will be correct if the original filter is the correct size. If there is no filter on the system or you need to determine what size filter you need, measure the size of the filter rack by following this procedure:
  1. Turn off the power to the furnace.

  2. Locate the filter rack on your system. If it’s a ceiling- or wall-mounted filter grill, go to step C. If the filter rack is located in the return duct at the furnace, go to step E.

  3. Open the clips on the grill and remove the cover.

  4. Measure the inside of the grill from end to end. If you measure the daylight opening, the filter you buy will be too small. Round your measurements to the nearest inch. For example, a measurement of 19 ¾ " X 19 ¾ " isa20” X 20” filter. Go to step L

  5. Remove the cover from the filter rack.

  6. Measure the height of the channel into which the filter slides.

  7. Measure the depth of the duct section into which you'll be installing the filter. If you can't obtain this measurement, Take a wooden dowel and insert it into the filter channel. Push it until it strikes the backend of the duct section.

  8. Mark the dowel at the point where the duct ends.

  9. Remove the dowel from the duct.

  10. Measure the distance from the mark you made to the opposite end of the dowel.

  11. The measurements obtained in steps F and J will provide you with the proper filter size for your system.

  12. With these measurements in hand, obtain your new filters.

How do I replace my air filter?

This is one of the simplest and most important things that you can do to ensure continued satisfactory operation of your heating system.
Changing the air filter involves locating the existing filter, obtaining a new filter, installing the new filter and ensuring that air is not able to bypass the filter, once installed.
The filter will be either in a central location,such as a hallway, or at the furnace itself. If you are able to locate a large grill in the ceiling or wall in a bedroom hallway, you will probably find your filter there.If the filter is in a central location, it's an easy task to open the front of the filter grill to get at it.
If the filter is at the furnace, there may be a sheet-metal cover over the filter-access port. This is to prevent unfiltered air from bypassing the filter and entering the appliance. In either case, here are a few things to keep in mind when replacing air filters:
  • There is an arrow on the side of the filter. This arrow should always point in the direction of airflow. In the case of the hallway-mounted filter grill,the direction of airflow is into the wall or ceiling, and away from the occupied space. If the filter is in the ductwork at the furnace, the arrow should point toward the heating appliance.

  • When removing the filter, be slow and deliberate. Do not shake, wiggle,smack or otherwise upset the dirt and dust that is peacefully resting on the filter's surface. Doing so will defeat the purpose of having a filter there in the first place.

  • Have a trash bag nearby when replacing the filter. The less distance you have to carry that dirty filter, the better.

  • Have extra filters on hand. It's inconvenient to have to run to the store to buy a new filter every month. And if you have an ample supply on hand, you'll probably change the filter regularly.

There are so many different types of air filters in the store. What type of filter is the best to buy?

With many things, the rule of thumb is to buy the best. But when it comes to air filters, this may not be the case. Will your car drive better if you use only the best grade of gasoline?Probably not. Will your furnace work better with the best filter? Maybe. Better filters, well, filter better! The fibers are closer together so they remove more particulates from the air. But these filters offer more resistance to airflow,making it harder for the blower to move the needed air volume through the system. And since we are now filtering better, we're collecting more dirt on the filter's surface, increasing the resistance to airflow even further. This reduces the amount of air that the blower is moving.If the blower can't move air through the appliance at the intended rate, the appliance can't do a good job of transferring the heat it generates.This may cause the appliance to overheat and shut down on its safety device.
The best filter to use on your system is the filter that meets the recommended guidelines of the system. If you are planning to upgrade to a more efficient, filter,check with a heating professional first.

How often should I change my air filter?

It depends on the type of filter you are using. If you purchase a standard, inexpensive, cardboard-framed filter, recommended that you replace it once a month. Filters classified as extended-surface-area filters will last longer. We call these pleated filters and they look like this:

When you purchase a filter, the paperwork that accompanies it will give you with the specific criteria. You can also find information printed right on the filter itself. The filter shown here, for example,is a 30-day filter.

Can I clean the old filter?

It depends on the type of air filter. If it's a cardboard-framed,fiberglass (or similar) filter, don't try to clean it. These filters,even when new, do not capture small particulates,and are not very efficient.

If the filter is a permanent-media filter (such as metal) you can clean it. The best way to clean these filters is to push out the dirt in the direction opposite to the direction that it has entered.

If you are cleaning the filter in a sink, place it dirt-side-down and run water onto the clean side. This will push the dirt out of the filter rather than shove it deeper into the filter. You can brush or vacuum it, but washing is the most effective way to get the job done. And be sure to wash away all of the dirt because dirt and water, will make mud, and mud doesn't let air flow by easily.

What is an electrostatic air filter?

This filter captures dust and particulate matter and operates on the principle that opposite charges attract. These filters have a permanent charge that attracts dirt particles as they pass through the filter medium. When the filter gets clogged or dirty, you can remove it, wash it, and put it back in.

What is an electronic air cleaner?

This is a higher-efficiency filtering device that combines a standard air filter with an electrostatic filter in a single device.

The electronic air cleaner is a multistage filtration unit that has a prefilter, a charging section, a collection section and a charcoal-filter section. The prefilter captures larger dirt and dust particles before they can enter the charging and collection areas. The prefilter acts like standard air filter.

After passing through the prefilter, the air next passes through a charging section.Here, the dust and dirt particles pass through a magnetic field and receive an electrical charge. The air, dust and dirt then pass onto the collection plates.

The collection plate attracts the particulates because the charge we gave them in the charging section is the opposite of the collection plate's charge. The dust and dirt particles adhere to the plates. The cleaner air now passes through the charcoal filter, which removes odors and gases that may be present in the air.

Is an electronic air cleaner better than a standard air filter?

Standard air filters remove only the largest particles, and although they often contain a dust-catching adhesive,they are not the most efficient filters available. But given their reasonable cost, they provide ample filtration for the average person,as long as you replace them once a month.

Although much more expensive (in both first cost and operating costs), an electronic air cleaner provides a degree of air filtration and cleaning that far surpasses that of the standard air filter.

How do I maintain the electronic air cleaner?

The prefilter on an electronic air cleaner is a permanent, metal-mesh filter that you can clean by running water through it. Place the filter in the sink, dirt-side-down, and then let the water to push out the dirt from the same side through which it entered.

Clean the collection plates according to the recommendations of the manufacturer.Many manufacturers allow you to put the plates in your dishwasher, and that makes cleaning quick,effective, and easy. Pay attention to how you remove the plates from the cleaner so that putting them back will be easy.

The electronic air cleaner is a power-consuming appliance, so make sure you disconnect the power to the appliance before you open or clean the prefilter or collection-plate section.