How to Choose an HVAC Air Filter for Your Home

Check out these tips on how to choose an air filter for your HVAC (i.e., furnace or heat pump), when, and why should you replace it. What are MERV and HEPA? Check out the benefits of a good quality filter and what can go wrong if it is not well maintained.

Does your heat pump need a new filter? Why?

Filtrete MPR 2200 16 x 25 x 1
(available on amazon.com)

Air filters are essential parts of heat pumps and other HVAC units. Filters are designed to help homes and businesses improve air quality and keep an HVAC unit’s components functional and efficient. So, if your heat pump is failing and you’re sneezing more often, you may want to check the filters.

Keep in mind that filters have a short life cycle because they become clogged fast.

So, when should I replace an air filter?

It usually depends on the unit’s specifications. The specs determine how often you need to clean or change the air filter. For example, fiberglass filters need to be replaced every one to three months. On the other hand, electrostatic filters only need maintenance and will take years before getting replaced.

You need to change your filter often if it’s clogged, damaged, or there is already mold growth on it. Good quality filters are important for making the unit last longer, and your family from getting sick.

Importance of a good quality filter

Here are some benefits of having a top-quality filter and the risks of not having one:

Lesser health risks

Air filters are a home’s first line of defense against pollutants. Depending on the kind of filter the heat pump or furnace has, it can remove a wide range of contaminants like dust, fur, and mold spores. Simply put, having good air filtration will keep your air clean and fresh. This will help keep your family from getting sick, especially if they have asthma or airborne allergies.

Properly working heat pump components

A clogged or unfit filter will lessen your heat pump’s airflow and overwork the unit. The evaporator coils, ducts, and the motor will be most affected by the restricted airflow. Here’s a brief rundown on how these parts will get affected:

• Evaporator coils and compressor – heat and air won’t move properly in the coils if the air filters are not working. The coils might freeze up if this happens, causing it to fail eventually.
• Ducts – dust, debris, and mold in the ducts mean that the other components are affected, especially the airflow. Having these pollutants in the air might also pose a health risk to you and your family.
• Air handler/motor – The motor will be forced to pull in more air if the air filter is either dirty or not working. Low airflow would lead to overburdening the motor and causing it to fail from overheating.

In short, a good quality filter helps ensure that all of the heat pump’s components will work properly through the good airflow. In addition, it keeps the unit energy-efficient, which is another benefit of having a good quality air filter.

Energy efficiency

Dirty filters can overwork heat pumps, consequently consuming more energy. HVAC units usually consume 3000 to 5000 watts of energy, and an overworked unit may use up more than that. Having a good quality and clean air filter will keep air flowing properly. With good airflow, a heat pump’s parts can function more efficiently and longer.

These are only some of the common benefits of having unobstructed air filtration. However, you can’t just buy a filter at random. You need one that fits your needs and wants and matches the specs.

Size

Air filters come in many sizes where the typical depth or thickness is between 1 and 6 inches. There are no standard filter sizes because it varies from one heating system to another.

It is important to get a properly sized air filter and avoid air seepage, low performance, stress on the system, and higher energy bills.

So, if your furnace is using a filter with a dimension of 16” x 25” x 1” (width x length x depth), get the same size. The size is usually written on the filter. If you have to measure it, take the actual size and round it up to the nearest whole number (if the actual size is 15.5” x 24.5”, round to 16” x 25”). When installing it, match the arrow marked on the filter with the airflow, going from the duct toward the furnace.

How to choose a quality air filter

When thinking of which type of filter to use for your HVAC, consider the following:

• Family members with respiratory problems like asthma or allergies
• The ages of the family members (are there children or elders in your home?)
• Pollutants you wish to filter (e.g., dust, mold spores, pollen, fur, bacteria, etc.)
• Outside ventilation
• Pets and smokers in the home
• Energy efficiency
• Maintenance simplicity
• Filter size (i.e., 1” filters versus 4” filters)

We need to consider these because some filters are designed to capture only specific types of pollutants. Some of us also don’t need too much filtration, either. So how do we choose the right filter?

Choosing the right filter

You can use the Minimum Efficiency Reporting Value (MERV) number to evaluate an air filter. One is the lowest, and 16 is the highest, at least for standard air filters. When choosing filters, we recommend selecting a filter of MERV 8 to 12. The numbers are usually in the packaging.

If you buy a cheaper filter, the general rule is to expect to see the lower MERV number, which will remove only a smaller fraction of contaminants.

It is also important to consider the static pressure drop across the filter, so if there is too much restriction in the airflow, your HVAC unit will work harder and less efficiently, which will shorten the unit’s life and increase the operation cost.

Note: MERV was developed by ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) to report the effectiveness of air filters (Wiki).

Here are some options to help you decide which filter type to use:

Fiberglass mesh filters – these MERV 4 filters are cheap but not recommended because they don’t improve air quality. You can still use this kind of filter if there are only dust, lint, small bugs you’re filtering, or pollutants with the size ranging from 3 to 10 microns.

Pleated/Polyester filters – medium-quality filters that can capture more particles than fiberglass filters, usually around MERV 5 to 8. Such filters can capture up to 90% of the pollutants sizing from 3 to 10 microns. Their disposability makes for easy maintenance because they can be replaced every one to three months.

Electrostatic filters – these filters clean the air by using static electricity (cotton or paper fiberglass). Electrostatic filters have disposable and permanent versions. Permanent electrostatic filters can last up to eight years and can be maintained by washing and air-drying them. These filters are a good pick for standard heat pumps with a MERV rating of 9 to 12. These filters are recommended for homes with pets and smokers.

High-efficiency filters – these filters are the best for your home. They are the most effective types because they can capture up to 95% of pollutants with the size down to 0.3 microns, including pollen and mold.

HEPA (High Energy Particulate Air) filters – these are hospital-grade filters with MERV 17 to 20. They provide the best filtration system; however, they require special installation.

UV filters – these high efficient filters are also designed with UV lights to kill the germs.Apart from choosing the right filter, you also need to know how to maintain it.

Air filter maintenance

Different filters have different ways of maintenance. Some can be disposed of while some only need to be cleaned. But first, how often should an air filter be changed?

How often to change an air filter

When to change a filter depends on the filter type. Fiberglass filters should be replaced every 30 days, while you can keep pleated ones for up to 3 months. Regardless, make sure to check air filters every 3 months to see if you need to clean or change it.

However, if someone in your family has asthma and/or you have pets, you need to check more frequently. Checking every six weeks is good enough. It might also be time to change the filter if your heat pump does not meet your desired temperature or if the air quality has dropped.

How to change a filter

Procedures for changing your air filter vary slightly depending on where your filters are. But they boil down to the following steps:

Find and open the filter cabinet. Don’t forget to turn off your system before doing so. Filter cabinets are usually in the basement. Be careful when sliding it off.

Clean or replace your filter. Replace the filter if it can’t be cleaned or used anymore. Otherwise, you can wash down the filter or clean it according to the manufacturer’s recommendations. For electrostatic filters, for example, it needs to be washed and air-dried before re-inserting. Don’t forget to measure the air filter if you’re getting a new one.

Re-insert the air filter and turn your unit on. Make sure the filter is snug in its place. If it moves, you need to replace it with the right dimensions.

Conclusion

As you can see in the above text, it is not recommended just to install a filter and forget it. It is essential to replace it regularly and as directed by the manufacturer.

Most filters are either easily disposable or easily maintainable. Your needs and wants should determine the most suitable air filter for your heat pump at the end of the day.

You can buy air filters in any hardware store or online. If you buy a filter at Home Hardware or Lowe’s, expect to pay a full retail price, but if you go online and buy in bulk, you will save time and money and will be set for a year or two.