What’s the Right Air Filter For You?

by | Mar 27, 2020 | HVAC Blog

What’s the Purpose of the HVAC Air Filter Anyway?
The primary purpose of your HVAC air filter is to protect the coils from getting caked with dust, dirt and debris.

Why’s Protecting the Coils So Important?
The coils are the most important part of your heating and air conditioning system because that’s where heat exchange action happens. Coils simply can’t transfer heat efficiently if they are blanketed under a layer of dirt or pet hair.

Consider Your Air Filter Inexpensive Insurance!
The filter simply grabs dirt and debris before it lands on the coils. A properly sized filter only allows airflow to go through it, not around it. Your filter will get clogged with dirt if it’s not replaced regularly. A clogged filter means air can’t pass through it easily, so the motor has to push harder to force air through the blocked filter. Extra work causes wear and tear on the blower motor, ages your equipment prematurely, and shortens its life over the long haul. And all the while your unit is rapidly aging, it will cost you more to heat and cool your home! It’s critically important to change the filters, keep coils clean and have regular maintenance.

dirty filter

This filter is full of the filthy stuff that would cover your condensing coils, not to mention cause breathing problems!

What Does “MERV” Mean?
Air filters are not all made the same. Some remove more dirt (or particulate) than others. It helps to understand the rating system used to measure how effectively a filter removes dirt from the air before the air reaches your tender coils. The American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) developed the MERV (Minimum Efficiency Reporting Value) considered the industry standard. The “MERV”, or how well the filter removes airborne particles, ranges from a minimum score of 1 to a high of 20.
Keep in mind, the lower the MERV rating the open the filter is to airflow. The higher the MERV rating, the tighter the spaces are in the filter medium and the more restrictive the filter is to air flow.

There Are Two Basic Types of Air Filters – Mechanical & Electrostatic:
1. Mechanical Air Filters remove airborne particles by physically blocking and catching them on the filter material as they fly through it.

Simple mechanical filters are the most common filters used in most residential & light commercial heating and air conditioning systems.

a) Basic Flat Fiberglass or 1 To 2-Inch Pleated Disposable Filters (MERV 1 – 4) are only intended to protect your HVAC equipment from buildup of dirt and grime on the coils by removing large particles which haven’t yet settled on your furniture and carpets. Replace them every 1 to 3 months, depending on how dusty the environment is at a cost of only about $2 – $3. The advantage to using them is they are a very inexpensive way to protect your investment – as long as they are replaced regularly. They are a good choice for renters and people without pets, allergies, asthma, smoking or lung disease. They do not clean the air you breathe.
b) Disposable Pleated Cotton or Polyester Mechanical Filters (MERV 6), are more efficient and remove even some medium-sized particles like spores and mites. They’re not very good at getting rid of smaller particles which fly right through. They do need to be monitored for replacement a little more frequently than less efficient filters to avoid clogging-up – precisely because they catch more dirt. Be prepared to change them monthly if you have pets or dusty hobbies, or at least every 3 months. The advantages are you can upgrade to them yourself, only cost about $5 – $6, can be made of green materials and do actually clean the air you breathe of some small particles. Disadvantages: A neglected dirty filter will quickly begin to block air flow, which makes your system work harder, use more energy and cost more to operate; Smaller particles, which irritate respiratory conditions, are not caught by these filters.
c) A Five-Inch Medium-Efficiency Filter (MERV 7 – 13), is an easy and cost-effective (about $6 – $9) DYI upgrade from a standard 1 to 2-inch filter because it can be about 20-times more effective. Studies show these filters give you the best balance between ability to remove small particles and allergens and reasonable replacement cost. The Environmental Protection Agency (EPA) says for some small particles, a filter rated MERV 13, for about $39, will actually decrease indoor particulates about 80 percent – making breathing easier for people with allergies.
d) The Activated Carbon Media Filter (MERV 8) is a special kind of mechanical filter that works on the molecular level to remove odors and dust because of its ability to catch very small particulates in its crevices. “Activated” means the carbon media was super-heated to open up cracks in the carbon to increase surface area and allow maximum absorption. Replaced every 2-3 months, they cost $8 – $30 each, depending on size.
e) HEPA (High Efficiency Particulate Air Filters, MERV 17-20) are recognized by the Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency (EPA) as the definitive hospital-grade solution in purifying air. They catch 99.97% of dust, smoke and bacteria, including very fine particles, like viruses, down to 0.3 microns. These filters are highly restrictive and get more restrictive as they collect particulate. They require powerful fans to push air through them, therefore most residential HVAC systems can’t be retrofitted with HEPA filters.
2. Electrostatic Air Filters use a charged filter medium to trap dirt like a magnet.

f) Simple Disposable Electrostatic Filters (MERV 10) contain self-charging electrostatic cotton or paper fibers that act like magnets, attracting and trapping small particles, making them a good choice for homes with children, pets and smokers. While you can DYI and the cost is affordable in standard sizes, about $15 – $20, custom sizes can be expensive, and like simple filters, they must be monitored and replaced regularly.
g) Permanent Washable Electrostatic Filters (MERV 9) are similar to disposables in that they contain self-charging cotton or synthetic fibers which attract particles, but they are washable and can be reused for six to eight years. They are environmentally friendly and are affordable at about $50 – $120 depending on size. The ‘High-Efficiency’ version (MERV 13-16) are large like HEPA filters – and they are often confused with them! They must be professionally installed in a special housing due to its size. They have high filtration capability and are used in hospitals where they filter out the smallest particles to prevent the transmission of airborne infection. While these filters cause somewhat less airflow resistance as compared to HEPA filters and support quieter operation of the blower fan, they are just too effective in that they prevent good air circulation in residential applications. The end result of less air circulation is worse air quality in your home.
h) Whole House Electronic Air Cleaners, are 3-stage units which are retrofitted into your home by your HVAC professional to clean all the air in your home. All particles, large and small, are positively charged as they pass through and are then collected on a negatively charged collection surface. This process of ionization produces a very small amount of ozone which sensitive people might find irritating. They are great at filtering out very small particles, odors and cigarette smoke without causing too much air flow resistance. While portable air cleaners are popular and inexpensive, they are ineffective because they only clean air in the room in which they are located while your heating and cooling system are circulating dirty air throughout your whole house. Whole House Electronic Air Cleaners are permanent, meaning there is no filter disposal, but that the collection plates should be washed every 2-3 months.

If you or someone you care about has breathing problems worsened by pollen and dust, the professionals at Oasis can help with your questions about air quality. Call Oasis at (520) 648-1755!


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