The air filter is one of the most critical components of the HVAC system. Furnace filters not only prevent the system from getting clogged up with dust and debris but also clean the air in your home.
As they are essential to the system’s function, they must be maintained and kept clean. But how much should one spend on the right filter?
|Cheap Filters||Expensive Filters|
|Tend to be made of woven fiberglass||Usually polyester or cotton|
|Need to be changed monthly||Change at least every three months|
|Filters only large particles||Filters smaller particles|
|Better airflow||Denser material restricts airflow|
More expensive filters will cost more not only at the register but also when paying energy bills. Conversely, the more expensive one will filter more and provide better air quality.
Read on to learn more about each filter so that you can better decide which one best fits your needs.
MERV, or Minimum Efficiency Reporting Value, is the most common system to measure an air filter’s filtration capabilities and range from 1- 20. The range you’re likely to be looking to use will be between 5 – 12.
- MERV 1 – 4 – These filters capture particles greater than 10 microns (dust mites, bugs, spray paint dust, carpet fibers), which will keep the inside of your furnace or air conditioning unit clean but will do next to nothing to improve air quality.
- MERV 5 – 8 – These filters capture particles greater than 3 microns (mold spores, pet dander, aerosol sprays, and cement dust).
- MERV 9 – 12 – These filters capture particles greater than 1 micron (humidifier dust, lead dust, auto emissions, Legionella bacteria, milled flour). These are the filters likely to be used in a hospital laboratory but can also be found in residential buildings.
- MERV 13-16 – These filters capture particles greater than .3 microns (all bacteria, tobacco smoke, sneeze droplets). These are the best you will find in a residential setting, but these are the type of filters used in Surgery and Hospital Inpatient rooms.
- MERV 17 – 20 – Filters virtually everything (viruses, radioactive radon). This level of filtration will typically be found in cleanrooms used when manufacturing electronics or conducting scientific experiments.
Source: CoolRay; Davis Air Conditioning & Heating; Grainger; Environmental Protection Agency; Engineering Toolbox
Does Increased MERV Decrease Air Flow?
While those high MERV filters are great at filtering debris and cleaning the air in your home, they reduce the air pressure in your duct system. This could potentially raise your energy bills and take a toll on your furnace or air conditioning unit.
Filterbuy argues that the increased surface area of a pleated air filter actually improves airflow. However, you should consult your furnace or air conditioning unit manual for the recommended MERV rating. Why? Because going above this causes airflow issues.
The Air Conditioning Contractors of America (ACCA) standards for HVAC design assume that pressure will drop across an HVAC unit’s air filter by .1 i.w.c. (inches of water column).
A study by the ASHRAE found that filters with a MERV rating of 4 or less met this standard, while a filter with a MERV rating of 8 doubled the pressure drop, and a MERV rating of 11 tripled it.
The ACCA standards and the findings of this study support an argument that air quality improvement is not what HVAC systems are designed for.
The air filters are intended to keep HVAC systems clean so they can work properly. Allergens, spores, and other irritants will not affect an HVAC’s performance, but a lack of airflow will.
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Source: Home Energy; Proctor Engineering Group; Energy Vanguard; TR Miller Heating and Cooling
Does Decreased Air Flow Affect Energy Consumption?
Yes, but apparently not as much as it used to. The same study that measured the drop in air pressure in relation to the MERV rating concluded that,
“high-efficiency filters did not have much of an impact on energy consumption in residential air-conditioning test systems.”
Alec Lower writes for Second Nature that innovations in HVAC design have made the systems more efficient, to the point where less airflow is needed for them to operate smoothly.
So, why do so many HVAC techs and experts recommend the cheap fiberglass filters?
The recommendation of fiberglass air filters by HVAC techs is due to the number of homeowners who neglect to change their air filters at all.
Since fiberglass filters won’t capture as much, it’s less likely to create enough blockage that will overwork and damage the system.
Related: Why Furnace Is Not Blowing Hot Air?
From the cheapest of the cheap to the best and most expensive, all filters need to be maintained. As mentioned in the last section, if your dirty filter is neglected, the buildup will cause a strain on the system. This will ultimately damage the motor and reduce the lifespan of your HVAC system.
1. Woven Fiberglass Filters
It’s strange that HVAC techs would recommend cheap fiberglass filters to people that can’t remember to change them.
Due to having less surface area, fiberglass filters need to be changed more frequently than their pleated counterparts.
While it may not cause airflow issues, a clogged fiberglass filter will allow debris to pass through, eventually clogging the system itself.
2. Pleated Air Filters
Your pleated air filter is typically rated to last three months before being changed. However, this can vary depending on environmental factors.
If you have pets or live in a particularly dusty environment, your filter will likely need to be changed more often.
While these filters may cost more, the trade-off is that you don’t have to buy them as frequently as filters that need to be changed monthly.
3. Washable Air Filters
There is an option to buy a permanent air filter. The washable air filter hasn’t been mentioned because it doesn’t fit well into either category: it costs more to purchase (upfront, at least), but it has the filtering capabilities of the cheap fiberglass filters with a typical MERV rating of 4.
Washable air filters will save you money in the long run, as you aren’t buying replacement filters, but it will not save effort.
They need to be washed monthly to remove buildup, which isn’t hard; it can be done with a water hose or in your bathtub.
However, in addition to the time it takes to wash the filters, they have to be allowed to dry completely before replacing them.
Placing a filter with any moisture back into the HVAC system creates an environment ideal for mold growth, which will then be circulating into the air you breathe.
Source: Air Treatment, Inc.; Snell; Air Filters Incorporated
Filters for Allergies
While cleaning the air you breathe may not be what the HVAC system was designed for, it’s a nice bonus.
Perhaps air filtration to relieve your allergies is a higher priority than energy efficiency. If that’s the case, a MERV rating of 10 is likely as low as you’ll want to go.
If allergies are a concern, change your filters more frequently, especially during high pollen times.
Your air filter is only one part of your HVAC system to consider. The right filter will help reduce irritants and allergens in the air, but the rest of the system needs to be maintained and kept clean as well.
If not using the right filters and changing regularly, dust, pollen, and mold spores could accumulate in your system and ducts.
A few alternatives to laying the burden of keeping your air clean on your HVAC system and its air filter are:
- Install an Electronic Air Cleaner. An electronic air cleaner is a device that is installed in the ductwork of your HVAC system that typically filters with at least a MERV rating of 13. This can be expensive and will be most cost-effective to install with a replacement or new HVAC system.
- Clean up. Making an effort to reduce the pet dander, dust, and mold in your home will also reduce the amounts in the air you’re breathing.
- Keep Your Plants Outside. Yes, your indoor plants are producing oxygen; they are also collecting and fostering mold growth.
- Place air purifiers around your home. Not to be confused with electronic air cleaners, air purifiers are much smaller machines that purify the air of the room it’s in.
Source: Arista; Golden Rule PHC; Molekule; Pharo Heating & Cooling; Harvard; NY Times
Furnace Filters and Air Conditioning Filters
It turns out both furnaces and air conditioning units use the same filters and serve the same functions.
So, while this article might be about furnace filters, the information will be relevant even if you live in a region where central air conditioning units are more common than furnaces.
There are multiple factors to consider when choosing the best air filter for your furnace (or central air conditioning unit).
First, what are your filtration needs? If someone in your home has allergies and you don’t have an air cleaning alternative, then you should likely choose a filter with a higher MERV rating (at least 10).
Next, how old is your HVAC system? If it’s relatively new, it likely won’t hurt your energy bill to use a higher MERV rating.
Test different MERV ratings when you change your filters, and look for a noticeable change in performance. If it’s an older system and allergies aren’t an issue, try a mid-level MERV rating of 8. This will save some money while getting adequate filtration.