Furnace filters play a vital role in extending the life of the HVAC system and reducing service call costs. With preventative maintenance inspections right around the corner, I'd like to highlight the importance of one of the commonly addressed issues and give some insight into the quality variance of filters.
Current Procedure and Tenant Responsibility
The Legerity Property Management lease agreement states that tenants are responsible for cleaning or replacing the furnace filter and that any service calls directly attributed to lack of said maintenance will be billed to the tenant. As such, tenants are always asked to replace the furnace filter before submitting a maintenance request for HVAC issues.
Efforts to reduce wear and tear through tenant education and compliance
Tenants are educated briefly about the importance of furnace filters during lease orientation, often again upon moving in - showing those that are unfamiliar with proper maintenance, and then again if needed during maintenance inspections. Furthermore, common filter sizes are on hand during maintenance inspections so that we can replace them right then and have the tenant pay for the filter accordingly. Additionally, if the tenant uses filters for each individual air vent, they are asked to discontinue their use as they restrict airflow and aren't capable of filtering anything a quality furnace filter wouldn't have collected already. All tenants are referred to
The Filter Factory, which has all sizes, levels of quality, and most importantly free delivery and an automatic delivery program, so even if a tenant forgets between inspections, they have a filter coming their way automatically.
What makes one filter better than another?
The two primary considerations of any furnace filter are how well they protect the furnace assembly by trapping airborne particles and how much they restrict airflow. Filters least effective in the former actually restrict airflow very little, causing less pressure drop after the filter, but do little to protect the furnace components. Clearly, balance is key.
In most cases, a pleated filter with the greatest possible thickness is going to give us that balance, but let's explore the options on the market and variables that may affect filter choice.
For residential units, we have three kinds of filters: fiberglass, washable electrostatic, and pleated. Fiberglass filters are the cheapest and are the least effective, only filtering large particles accounting for about 10% of airborne particles. Molds, pollens, and other small particles pass right through. In short, they should never be your first choice except in rare situations where airflow is limited.
Washable electrostatic filters are slightly better - filtering between 15 and 25% of particles.
Pleated filters are the ideal choice although they have air pressure drop considerations dependent on their MERV rating and thickness. The MERV rating denotes the size of particles the filter collects and how effectively they do so. The higher the MERV rating, the smaller the particles it can collect. The commonly recommended MERV 8 filter can effectively collect particles in the 3 to 5 micron range, which includes molds and some allergens, while MERV 11 can collect particles in the 1 to 3 micron range, including insecticide dust, paint pigments, copier toner, and some bacteria/organic contaminants of concern.
Air pressure drop, caused by the air resistance of the filter, has a negative effect on system performance as the system has to work harder as the airflow is restricted, causing additional wear. Furnaces are designed to operate with some pressure drop, but the less resistance, the more efficiently the unit is able to work as it has to work less to circulate the air. The MERV 8 is most commonly recommended because it has a good balance of filter performance and air resistance while the MERV 11-13, particularly popular among those with allergies and others concerned with limiting some pollutant exposure, does indeed restrict airflow more than the MERV 8, so it becomes more important to be sure it isn't allowed to get too dirty before replacing. The smaller the particles the filter can collect, the more air resistance you can expect generally; however, the thicker the filter is, the less air resistance/pressure drop.
Pleated filters usually come in 1", 2", 4", and occasionally 5" thicknesses. Although furnaces typically have racks installed that only accommodate a 1" filter, there are major advantages to thicker filters. First, a 4" filter has 4x the surface area of a 1", so the air can more easily pass through, meet less resistance, and cause less pressure drop, improving system efficiency and potentially reducing wear and the utility bill. The second major advantage is that with increased surface area comes a greater capacity to hold particles over time. Whereas most 1" MERV8+ filters should be replaced every 2-3 months, a 4" filter has a lifespan more along the lines of 6-12 months. With the thicker filters, the wear and tear from the filter not being replaced right when it should be is of considerably less consequence, which can be important when inspections are being done roughly every 6 months.
One other way that some systems improve surface area is by putting 2 filters in a V-shape, doubling the filter media surface area. Putting two 1" filters on top of each other would NOT increase surface area, but would greatly increase the pressure drop as the air would meet twice the resistance as it has to pass through two filters instead of one.
In summation, using the thickest possible pleated filter with a MERV8-MERV11 rating and ensuring it is changed at proper intervals equates to a longer lifespan for your HVAC system and cuts down on repairs during its life caused by debris accumulation on system components. For new construction and installations, ask for a 4" filter rack/access whenever possible.
Brandon Morgan
Legerity Property Management, Inc.
