Allergies: Filtering Out Pollen With Furnace Filters

Let fresh air in, keep dust and pollen out

For allergy sufferers, open windows bring fresh air but also pollen and dust. A window filter lets you keep the fresh air while blocking the misery-causing pollen.

By the DIY experts of The Family Handyman Magazine

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What allergy sufferers need to know

The claims made by furnace filter manufacturers are true: A high-efficiency filter can provide some relief from allergies. By trapping smaller airborne particles, these filters make the air in your home cleaner and less irritating to allergy sufferers. But before you install a high-efficiency filter, there are a few things worth knowing:

  • High-efficiency means higher cost. If you’re currently spending $20 per year on cheapie filters, prepare for sticker shock. You can easily spend $100 per year on high-efficiency filters.
  • What the numbers mean. Furnace filters are labeled with a numerical efficiency rating. A higher number indicates higher “efficiency.” That simply means the filter traps smaller particles. When it comes to furnace filters, “efficiency” does not mean energy savings.
  • The numbers are tricky. MERV is the most common rating system. But some filters carry “MPR” or “FPR” ratings. A MERV 13 is roughly equivalent to an FPR 10 filter. Luckily, there are several charts online to help you convert the numbers. Just search for “MERV vs MPR vs FPR.”
  • Higher isn’t always better. If no one in your home suffers from allergies, there’s no reason to go higher than MERV 7. For allergies, MERV 11 is your best choice because higherrated filters cost more but don’t provide much extra relief.
  • Don’t trust the life-span claims. Filters carry claims like “lasts up to 90 days.” But the life span of a filter depends on how clean the air is in your home and how much your heating/cooling system runs. No manufacturer can possibly know that.
  • Filters are not enough. Furnace filters help, but for allergy sufferers, reducing dust in your home is even more important. That mostly consists of frequent vacuuming with high-quality vacuums and filters and/or eliminating carpeting and rugs as much as possible.
  • “Efficiency” can wreck your furnace. High-efficiency filters have smaller pores, which can reduce airflow when new and even more as they clog. That can make the furnace overheat, causing it to shut down or burn out the expensive blower motor. The repair bills can easily run hundreds of dollars, not to mention the increased energy costs to run the stressed blower motor.

How Furnace Filters Are Rated

Many filter manufacturers follow the Minimum Efficiency Reporting Value (MERV) rating system established by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). The MERV number is an indication of the filter’s effectiveness at trapping particles. A MERV 1 filter traps dust bunnies but allows most dust to pass right through, while a MERV 16 traps bacteria and particles as small as .30 to 1.0 micron and is used mostly in operating rooms. If you don’t have allergies, a MERV 7 furnace filter will work just fine in your home. And if you do have family members with allergies, go up to a filter with a MERV 11 rating.

However, some filter manufacturers and retailers have developed proprietary rating systems like Microparticle Performance Rating (MPR) or Filter Performance Rating (FPR). Before you buy a filter based on an MPR or FPR rating, look for a MERV to FPR/MPR chart online (nordicpure.com/info/what-ismerv is one site) or contact your furnace service company for a filter recommendation based on your particular furnace.

Installing a window filter

Prevent Furnace Damage With a Filter Monitor

A filter that’s plugged with particles may not look dirty. And the manufacturers’ life-span estimates are nearly worthless. So how can you tell when a filter is dirty enough to stress your heating/cooling system? You can’t unless you install a filter monitor. They’re available in two versions:

  • Mechanical filter monitors are inexpensive and take about five minutes to install, even if you’re a beginning DIYer. They’re available online for less than $20 (search for “furnace filter monitor”). The downside is that it relies on your memory. If you forget to check it, you won’t know when the filter is clogged.
  • Electronic filter monitors let you know when the filter needs replacing. The unit shown (the FILTERSCAN WiFi; $100 online), for example, connects to your home’s Wi-Fi and sends an alert to your smartphone. Installation is as simple as driving a few screws. Just find a location on your return air duct and predrill holes (Photo 1). Then mount the unit (Photo 2) and follow the calibration and Wi-Fi setup instructions.

Other Strategies for Reducing Pollen

  • Upgrade your furnace filter to a high-quality disposable filter made of pleated fabric or paper. Or have a professional install an electrostatic filter that’s connected to your ductwork ($700 to $1,500).
  • Change your bedding weekly.
  • Replace carpet with wood, laminate, tile or vinyl. Carpet is the biggest reservoir of dust. Also vacuum area rugs weekly.
  • Take couch cushions outside and beat out the dust with a tennis racket. Or better yet, when it comes time for furniture replacement, choose leather or vinyl upholstery rather than fabric.

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.

  • Window air filter

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