HVAC Furnace Filter Basics | Indoor Air Quality - Pollen, molds, and dust are common in any household and can be reduced by using an air filter.HVAC Furnace Filter Basics To maximize the benefits from the cleaner indoor air you should use electrostatic furnace filters and air conditioner filters along with a high-efficiency air cleaner. Electronic Air Cleaners (EAC’s) can also offer you high-quality clean air over the typical cheap air conditioner and furnace filters on the market today. Clean the air in your home and breathe easier.

HVAC Furnace Filter Basics | Indoor Air Quality

Tiny particles small enough to inhale will pass easily through the cheaper air conditioning filters. To have good filtered clean air you’ll have to look at filter quality. Particle concentrations in your home are derived from dust which is pollen, dirt, dander and many other things that are in the air. These tiny particles float around the air in your home and flow through the HVAC air conditioner or furnace system. Particle buildup will decrease the efficiency of your furnace and air conditioner, as the furnace and air conditioner has to work harder to pull air through the clogged furnace filters and dirty air conditioner coils. More expensive filters can also improve the air quality in your house by removing pollen, bacteria, dander, dirt, and mold spores from the air.

Electrostatic and HEPA Air Filters | HVAC Furnace Filter Basics | Indoor Air Quality

Electrostatic filters are also good in this department. Electrostatic filters are filters that must be cut to fit and are more effective than the cheaper filters. What is an electrostatic air conditioner filter: It is a filter media that has an electric charge that attracts contaminants. It does this in one of two ways – they either have built-in electrostatic charges or create a charge from the air moving through the system.

Another type of filter is the HEPA (High-efficiency particulate arrestance) filter. HEPA-type air purifier filters are generally cheaper than True HEPA air purifier filters but do not filter particles as effectively. True HEPA filters are considered extremely effective at removing small particles from the air because they are able to stop 99.97 percent of those particles that are 0.3 microns in diameter or larger. True HEPA filters are used by many hospitals to keep the air clean and pure and prevent the spread of bad bacteria and virus through the air. There are HEPA filters available for residential systems. Call your local air conditioning and heating system contractor and ask them what they offer for HEPA-type filters.

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Filter Maintenance Frequencies | HVAC Furnace Filter Basics | Indoor Air Quality

Remember with the higher efficiency filters come the increased furnace filter maintenance. Why? Because the higher and more efficient the air conditioner filter is the more particles are going to build up and accumulate in the furnace filter. This means the higher efficiency air conditioner filters load up fast because they catch more particles. This is good for your health and for your HVAC air conditioner and furnace but it is not good for your furnace filter budget since you will have to purchase air conditioner filters more frequently. The alternative to this is the electronic air cleaner. Purchasing an electronic air cleaner will save you money in the long run from purchasing furnace filters on a regular basis. The electronic air cleaner can be washed on a regular basis and as long as it is clean it filters the air as good as HEPA filters. As the electronic air cleaner cells load up the electronic air cleaner loses its efficiency so regular maintenance is recommended to keep it operating and in top filtering capacity.

In a furnace, heat pump, or air conditioner system, the system is designed for a specific amount of pressure. Most manufacturers designed their equipment for ~.50″ WC or Water Column. With that specific pressure in the furnace, you get a specific performance of the furnace, heat pump, or air conditioner. When the filter loads up and blocks off airflow, you change that pressure inside the air handler or furnace. Too much blockage and you create problems by changing the designed pressure in the system. See the following chart for details and then a deeper explanation after you see the chart.

HVAC Furnace Filter Basics | Furnace Design Data for Pressure and CFM

Maintenance HVAC Furnace Filter Basics

Filter Maintenance and Furnace Pressure

So you can see from the chart above the specific design reference for pressure. At the pressure given (~.50″ WC), you get all the other design specifics listed in the chart such as:

  • Temperature Rise - this is a chart for a two-stage gas furnace with air conditioning so there are two different temperature rises given, one for high fire and one for low fire.
  • Cooling CFM
  • Heating CFM

There is more data on the chart but for filters, these three things are what we are looking at to illustrate the importance of keeping a clean air filter in the furnace. If the filter(s) get clogged and have an excessive buildup of dust and other particulates you change the pressure in the furnace. When you change the pressure you reduce the airflow or in the chart CFM’s. Lower CFM’s in heating mode means you will increase the temperature rise across the heat exchanger. Too much of a temperature rise across the heat exchanger and you will cause the limit switches to open. This means the furnace will stop heating because it has reached its high limit temperature capacity and the safety, the high limit switch, turns the furnace off so it will not get too hot and exceed design temperature.

In air conditioning mode, there is no high limit. However, when you don’t have the designed airflow across the evaporator coil the coil will freeze up. This reduces airflow even more and causes more ice to build up on the evaporator coil. The lesson here is to make sure you keep a clean air filter in the system or you will experience a malfunctioning system and lack of comfort as a result.

HVAC Furnace Filter Basics - Conclusion

It doesn’t matter what type of system you have you will need to have a furnace filter routine for checking and changing (or cleaning) the air conditioner filter. A minimum check time-wise is once a month air conditioner filter checks. Keeping those filters clean and keep your air conditioner and furnace in tip-top shape along with the air you breathe and your health.

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HVAC Furnace Filter Basics

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