How to buy a filter for your HVAC system

By · February 15, 2010 · Filed in Consumer Q & A's

Many people are confused with the conflicting information about which air filter should be used in their furnace and air conditioning system. The recommendations range from the “barely-filters” to filters equivalent to those used in a hospital clean room. Other choices include the “lifetime” electrostatic filters and the electronic “zapper” filters.

Let’s start with the goal. Your air conditioner manufacturer and many HVAC contractors recommend the cheap, almost see through filter because it keeps the equipment relatively clean and puts less strain on the equipment. We, on the other hand, recommend a filter with the highest level of filtration you can afford.

They recommend filters for the benefit of the equipment. We recommend filters for the benefit of the equipment and the people.

Does a better filter put more strain on the system than the cheap filter? Yes, but there are two solutions which can reduce the strain on the system while doing a great job of filtering out things which might be bad for the people. Both solutions make the return “bigger” by adding more square inches of filtration surface area to the return and therefore the system:

  • One way is to add another return in another part of the house the system services. A good choice to consider might be to add a filtered return to a bonus room or master bedroom area.
  • The other solution is to increase the surface area of the return by using a pleated filter. Pleated filters can fit in the same opening in the wall as your current filter and can range in thickness from one to four inches. A housing for a four inch pleated filter can be installed between the return opening and the unit when other options are not practical.

Buy the filter with the highest MERV and lowest pressure drop you can afford. What is MERV? MERV stands for Minimum Efficiency Reporting Value and is the way filters are measured. The best place to start is a MERV 12 or higher and one which is pleated one to four inches thick. They will cost a little more but they last longer, up to a year depending on conditions, and they do a much better job of cleaning the air. Electronic and electrostatic “lifetime” filters have no rating so avoid those.

A few more things regarding your filter:

  1. One is, make sure you have a tight seal around the filter, the interior of the filter housing, and the entire return ductwork. Otherwise, you will be sucking air from around the filter, the wall cavities, and the crawlspace or attic.
  2. Secondly, put your filter changes on a schedule to make sure they are performing at optimum levels. Either mark on your calendar or contract with a reputable company to monitor your filter changes, the cleanliness of your system, and your indoor air quality.
  3. Inspect the condition of your ducts by looking in the ductwork. Even the best filter will not keep dust from blowing out of your ducts if you need duct cleaning.

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