Indoor air quality work in Menlo Park, Atherton and Portola Valley comes down to three things a heating and cooling system can actually change: how many fine particles stay in the air, how dry or damp the air is, and how much outdoor air comes in and by what route. A useful visit measures those first, then looks at the filter, ducts and equipment that control them. You should come away with numbers and a short list of options matched to them.
What an indoor air quality test measures
| Reading | What it tells you | What usually follows |
|---|---|---|
| Fine particles (PM2.5), room by room and outdoors | Whether the filter catches what the house collects, or air slips around it | A better filter or filter cabinet, sealing gaps at the filter slot |
| Relative humidity | Air too dry in heating season, or damp in closed rooms over a crawlspace | A whole-home humidifier, or a drainage or moisture fix |
| Carbon dioxide | Whether occupied rooms get enough fresh air | Ventilation changes, sometimes an ERV or HRV |
| Temperature from room to room | Uneven airflow, often from the ducts | Duct repair or balancing |
| Filter, return, coil and drain pan | Bypass, a dirty coil, standing water, the source of a musty smell | Cleaning, drain repair, return sealing |
The outdoor reading is the yardstick: on a smoky or dusty day it shows how well the house keeps the outside out.
Filtration: where most homes start
The change that moves particle readings most is usually the filter: what grade it is, and whether air really goes through it. Many older systems have a one-inch slot at a return grille, built for a basic filter. A high-grade one-inch filter in that slot can restrict airflow enough to freeze an air conditioner’s coil or trip a furnace’s high-limit switch. The steadier route is a media cabinet that holds a deeper filter, typically MERV 11 to 13, with the gaps around it sealed. Static pressure is measured before and after, so cleaner air is not bought with a struggling blower.
Return leaks matter just as much. In houses with older ducts in the attic or crawlspace, where the filter sits at the grille, a split return pulls attic dust and crawlspace air in behind the filter, unfiltered. Sealing that leak is duct repair work.
Humidity, in both directions
Heating season dries indoor air, and summers on the bay side are dry too. A whole-home humidifier mounted on the furnace adds moisture through the ductwork. It needs a water line and a drain, and it earns its place only when readings stay low through the winter. Set too high, it fogs cold windows.
The opposite problem shows up in closed rooms over crawlspaces and in the lower levels of large homes: a damp, musty smell when the system starts. That often traces to a coil or drain pan that holds water, or to moisture in the crawlspace. The fix is drainage and cleaning, not a fragrance.
Ventilation: ERV and HRV
Tight remodels and newer rebuilds hold heat well but can let little fresh air in, which shows up as carbon dioxide climbing in bedrooms overnight. An ERV (energy recovery ventilator) or HRV (heat recovery ventilator) brings in a steady stream of outdoor air and exhausts stale air through a core that transfers heat, so incoming air arrives closer to room temperature. An ERV also moves some moisture; an HRV moves heat only. Fitting one means ducts to the outside, power and a filter on the intake. In an older, leakier house, sealing and filtration usually come before mechanical ventilation.
UV lamps: what they do and what they don’t
UV lamps mounted at the indoor coil keep the coil and drain pan surfaces from growing film, which can help with a musty startup smell. UV light does nothing to dust, pollen or smoke particles; that stays the filter’s job. If you consider a UV or electronic air cleaner, ask whether it produces ozone. You want one that does not.
Smoke days, foothill pollen and large homes
On wildfire-smoke days the system can either help or pull smoke in. Keep windows closed, run the fan with the best filter the system can take, and switch off an ERV or other fresh-air intake that lacks a good filter.
In Portola Valley and Ladera, wooded hillside lots bring heavy pollen in spring and dust on dry, windy afternoons. Filters there load faster and need changing sooner.
In Atherton, large homes often run two or more systems, or one system split into zones with long duct runs. Readings are taken per system and per zone, because the air handler serving the main floor can test fine while the one feeding a basement level pulls damp air.
What moves the price
Most indoor air quality work falls between $200 and $2,000. A testing visit and a filter cabinet upgrade sit at the lower end. A whole-home humidifier needs water and drain connections; an ERV or HRV needs new duct runs and openings to the outside, and a home with several systems may need one per system. The final price is confirmed in writing after an on-site evaluation.
Before you approve any work
- Ask which findings will be documented and which items are optional upgrades.
- Check whether electrical, duct or drain work is included.
- Compare the after-readings with the before-readings once the work is done.
If someone has suggested cleaning your ducts, read when duct cleaning is worth it first. For comfort and bills rather than air, see energy audits.