Air Filtration for Modesto Homes

The San Joaquin Valley has some of the worst particulate pollution in the country, in two seasons: winter, when fog and inversions trap smoke and dust, and late summer and fall, when wildfire smoke drifts in from the Sierra.

Fog lying in the low ground between hills, with bare trees

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Two bad-air seasons

Winter

The same cold, still air that brings tule fog traps whatever is put into it. Wood smoke, traffic and dust build up under the inversion for days at a time. That is why the San Joaquin Valley Air Pollution Control District runs its Check Before You Burn program from November through February, restricting fireplace and wood stove use on bad days.

Smoke season

When fires burn in the Sierra or the Coast Ranges, smoke settles into the Valley and can stay for weeks. Fine particles from smoke get indoors through every gap in a house, and the furnace or air handler is the one machine that can pull them back out.

What your system can do

A forced-air system moves all of the house's air through one filter several times an hour while the blower runs. The filter's MERV rating says how much of the fine material it catches. The basic one-inch fiberglass filters many homes use are there to protect the blower, not your lungs.

For smoke, the EPA recommends a filter rated MERV 13 or higher if the system can take it. MERV 13 catches a large share of the fine particles in smoke. During smoke events, set the thermostat fan to "on" rather than "auto" so the air keeps moving through the filter even when the system is not heating or cooling.

The catch with older furnaces

A denser filter resists airflow more. A one-inch MERV 13 dropped into a slot designed for fiberglass can choke an older blower, especially on a 1980s furnace with a fixed-speed motor and undersized return. Symptoms: the furnace overheats and short-cycles, or the AC coil freezes. The usual fix is a media cabinet: a four- or five-inch-deep filter housing installed beside the furnace, which gives MERV 13 filtration with far less resistance and lasts six months or more between changes. A technician can measure static pressure to tell you which you need.

Return grilles, ducts and leaks

A filter only cleans the air that reaches it. Leaky return ducts in the attic pull in hot, dusty attic air past the filter, which is the opposite of what you want during smoke. Sealing the return side is less visible than buying a better filter and sometimes does more.

Portable cleaners

If the house has wall or floor furnaces with no ducts, as some older College Area and Graceada Park homes do, a portable HEPA air cleaner in the bedroom is the practical answer. In ducted houses they are a useful addition for the room where people sleep.

What to ask for

A static pressure reading on your system, a recommendation on MERV 13 versus a media cabinet based on that reading, and a filter size and change schedule written down. Be wary of add-on devices sold on vague claims about ions or ozone; California restricts ozone-generating air cleaners, and an ordinary good filter is the proven option.

Want better filtration before the next smoke event? Call and ask. A local heating and air company will look at what your system can handle.

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Common questions

What MERV rating should I use in Modesto?

MERV 13 if your system can handle it, especially for smoke. If your furnace is older or the return is small, a deeper media filter cabinet gets you MERV 13 without starving the blower.

How often should I change the filter?

One-inch filters, monthly during smoke and in the heavy heating and cooling months. Media filters in a cabinet, usually every six to twelve months.

Should I run the fan all the time during smoke?

During smoke events, yes, with a good filter in. It keeps the air passing through the filter. Close windows and set any fresh-air intake to recirculate.

Is a whole-house air purifier worth it?

A media filter cabinet usually is. Devices that rely on ionisation or ozone are not a substitute, and ozone generators are restricted in California.

Who installs a media cabinet?

An independent local heating and air company. We are an advertising and referral service; we pass on your request and do not do the work.

Other heating and cooling work in Modesto

Also serving

Filtration & Indoor Air is available beyond Modesto, across Salida , Riverbank , Ceres and Turlock .

Get help with filtration & indoor air

Say what the system is doing and a local heating and air company will get back to you about a visit. Answered Mon–Sat, 8am–6pm · after hours we call back the same day Or call (209) 842-0950. If you have no heat or no cooling right now, calling is faster.