A better HVAC filter does help with cedar fever, with two conditions the filter box leaves out: it only cleans the air that passes through it, and it only does that while the system is running. Choose the highest MERV rating your system can actually handle, keep doors and windows shut once the junipers start in mid-December, and know what the filter cannot reach. Here is what each of those means for a home in Leander or Cedar Park.
When cedar fever season starts in Central Texas
Cedar fever is a reaction to the pollen of Ashe juniper, the tree Texans call mountain cedar. Robert Edmonson, a Texas A&M Forest Service biologist, told AgriLife Today that the trees typically begin producing pollen in mid-December, peak in mid-January and taper off toward the beginning of March. He also says the Hill Country west of Interstate 35, where Ashe juniper is the dominant canopy cover, gets it worst. Leander, Liberty Hill and Lago Vista sit in that country.
The pollen moves on the weather. The Texas A&M Forest Service describes how the dry, windy hours immediately before and after a cold front trigger the pollen cones to open, and the pollen then blows for miles. Symptoms are fatigue, sore throat, runny nose, partial loss of smell and a slight fever in some people; AgriLife notes that a fever above 101.5 degrees points to something other than pollen. Ragweed and mold spores drive fall allergies, so a household sneezing in September and again in January is dealing with two different seasons.
What a MERV rating actually measures
MERV, Minimum Efficiency Reporting Value, measures how well a filter captures particles between 0.3 and 10 microns, according to the EPA's explanation of MERV ratings. Its table shows a MERV 8 filter catching at least 70 percent of particles between 3 and 10 microns, MERV 11 at least 85 percent, and MERV 13 at least 90 percent. The gap widens at smaller sizes: MERV 8 carries no rating below 1 micron, while MERV 13 captures at least 50 percent of particles between 0.3 and 1 micron.
Whole cedar pollen grains are large on this scale. The Thermo Fisher allergen encyclopedia puts Ashe juniper pollen at 19 to 22 microns across, bigger than the largest particle the MERV test measures, so any decent pleated filter stops the grains themselves. What a higher rating buys is the smaller material in the same air: mold spores, fine dust and smoke. Filtration reduces airborne allergens and, in the words of the American College of Allergy, Asthma and Immunology, may provide some relief. "May" is the honest word.
Which MERV rating to use
EPA's recommendation is a filter rated at least MERV 13, or as high a rating as your system fan and filter slot can accommodate, and it adds that you may need a professional HVAC technician to find the highest efficiency filter that will work for your system. That second clause is the whole job. The fan and the slot set the ceiling, and the way to find it is to have the system measured rather than to guess from the box. Texas A&M's own cedar season advice is the same: higher MERV-rated filters in the home and car, and a home air purifier.
A home that wants more filtration than its one-inch slot allows needs a different slot, not a denser filter forced into the old one. That means a media cabinet or a whole-home purifier installed in the return duct. We install the Carrier Infinity air purifier, a MERV 15 system that Carrier reports as third-party tested to capture 95 percent of particles between 1 and 3 microns and 85 percent between 0.3 and 1 micron. It is the equipment behind our indoor air quality service, and whether a particular house needs it is an assessment, not a default.
Why the filter alone is not enough
A filter cleans nothing while the system is off. The EPA's guide to air cleaners in the home points out that HVAC systems run only when heating or cooling is needed, usually less than 25 percent of the time during the heating and cooling seasons. Cedar season is our mildest weather, so on a warm January afternoon the system may barely cycle while the pollen count is at its worst. Ask the technician what fan run time makes sense for your equipment.
The same EPA guide says no air cleaner or filter will eliminate all of the pollutants in a home, and that the most effective approach is to control the source and ventilate with clean outdoor air, with filtration as the supplement. For pollen, source control means keeping it out. The Asthma and Allergy Foundation of America's advice is to keep windows and doors closed and run the air conditioning; Texas A&M adds limiting time outdoors on high-count days.
Humidity, ozone and the filter change
Humidity is a separate lever. EPA's mold guidance is to keep indoor humidity below 60 percent, ideally between 30 and 50, and to use air conditioning or a dehumidifier when needed; the allergists at ACAAI say below 50 percent for allergy sufferers. Cedar season is dry, so this is mostly a summer conversation, and a whole-home dehumidifier is a summer install.
Skip anything that makes ozone. EPA says to avoid portable air cleaners and HVAC filters that intentionally produce ozone, and that no federal agency has approved those devices for use in occupied spaces. And change the filter: ENERGY STAR says to check it every month during heavy use and change it at least every 3 months, and EPA notes that an overloaded filter does not work well. During cedar season, check it monthly.
What to do before mid-December
Know your filter slot and the rating in it now. Have the fall maintenance visit include a check of what the blower can handle, so the filter you buy in November is the right one. Decide before the first cold front whether the household's allergy sufferers justify a media cabinet or a whole-home purifier, rather than deciding in January.
Comfort Pros is a Carrier factory authorized dealer serving Leander, Cedar Park, Georgetown and Liberty Hill, licensed under TACL# TACLB116912E. Call and we will tell you what your system can take, and whether a filter is enough.