Filters are all around us. There’s a water filter in your refrigerator, a cabin air filter in your car, an engine air filter in your car, a mask in your pocket, and most importantly (at least for this blog) an air filter in your home’s air conditioning system. Here are six key facts about air filters that will help you feel like a home maintenance pro.
1. Air filters are very important.
Air filters improve indoor air quality, but more importantly they protect the most expensive system in your home: your HVAC equipment, or as is commonly called the A/C system. HVAC stands for Heating, Ventilating and Air Conditioning, which are all the important functions performed by the often overlooked system in your attic.
All of the dust, dirt and debris caught in the filter would otherwise settle onto the heat exchanger in your gas furnace or the evaporator coil for your air conditioner. Removing the filters or forgetting to change them increases your potential for expensive repairs or replacement down the road.
2. You need one filter: not zero, and not two.
Newer HVAC systems often come equipped with a whole home filter located at the main air handler. In Houston single family homes, the air handler is almost always in the attic. If you have a whole home filter in place in the attic, do not install filters at the ceiling and wall grilles. Double filters will starve the HVAC system of the air flow it needs.
Whole home filters can be a great strategy, but the benefits probably do not merit upgrading unless you’re already in the process of replacing your HVAC system. If you’ve moved into a new home and you aren’t sure if you have one, check out figure 2 and figure 3 to get an idea of what you’ll be looking for in your attic.
3. Whole home filters or return grille filters are both good strategies.
While whole home filters are advertised as a higher quality of air filtration, my favorite building science resource still recommends filters at the grilles for several reasons. My philosophy on home maintenance is similar to good diet advice: the right strategy is one that you can stick with for the long haul.
If you have high ceilings or several different size return air grilles, go with a whole home filter. If getting in your attic is unsafe, or just not your idea of fun, go with filters at the grilles. Just set yourself a reminder with your filter size(s) for the next change date.
4. MERV 8-11 is a good range for your home.
The MERV rating system is the industry standard for filtration efficiency, or how effective a filter is at removing small particles from the air. Everyone except for Home Depot, who annoyingly has their own system, uses the MERV rating scale for air filters. A MERV 1 would be a filter that removes almost nothing. Filters that cost less than $5 each and do not advertise the MERV rating are likely MERV 1 or 2, at best. If you can see through the filter, like the filters in figure 4, it isn’t very effective.
A MERV 16 would be suitable for a hospital operating room but would starve your residential HVAC system of proper air flow. Filter King recommends MERV 8-10 for your home, but I’m going to add MERV 11 as a good option too. You can find plenty of recommendations for MERV 13 or higher by air quality experts, but those are advertised as hospital grade and HVAC technicians would tell you the reduction in air flow isn’t a good trade off for the life of your system.
5. Filter change frequency depends on home use.
The right frequency for changing your filters will depend on home use. To elaborate on the example from Paschal’s blog, a vacation home may have a MERV 8 filter and change it every 9 months, although that would be an extreme case. For a household with multiple pets and allergy sensitivities, you might go with a MERV 11 and change every 60 days. You’ll be spending significantly more in the second example, but the online suppliers offer steep discounts for bulk buying.
6. Analysis paralysis is a threat to proper home maintenance.
Even as a home inspector, I find the number of choices, sizes, ratings and pricing overwhelming. The key to sticking with good home maintenance strategies is planning ahead. For whole home filters, you are usually limited to the HVAC manufacturer’s specifically designed filter for the housing already installed. If you find this filter cost prohibitive or too inconvenient to access, there is nothing wrong with leaving the filter housing empty (like in figure 3) as long as you’ve installed filters at the ceiling or wall return air grilles.
I recommend spending a few minutes picking the right strategy for you and your family, shopping around online to lower the cost per filter, then setting yourself a recurring reminder for changing your filter(s). With an air filter strategy in place, you can kick back and spend time enjoying your home!