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Indoor Air Quality

Indoor Air Quality in Los Angeles

Almost everyone sells you step four.

A filter does very little on a house whose ducts pull attic air in behind it, and which refills with cooking fumes and off-gassing faster than it clears them. Here is the whole sequence, in the order that actually works.

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The process

Five steps, in this order

Each one makes the next one work. Done out of order, you spend more and get less — which is the single most common thing we walk into.

  1. 1
    Identify

    Find out what is actually wrong

    Measure particulate, humidity, ventilation rate, static pressure and duct leakage. Half of what gets blamed on air quality turns out to be airflow, and the two need completely different fixes.

    Skip this and you are buying equipment for a problem nobody has confirmed you have.

    Air quality testing →
  2. 2
    Remove

    Take out what is already in there

    Where there is genuine contamination — visible mould, vermin, construction debris, or enough dust that it reaches your rooms — it has to physically come out before anything else is worth doing.

    But only where conditions warrant it. We will tell you when they do not.

    Duct cleaning →
  3. 3
    Seal

    Stop it getting back in

    Leaking ducts pull attic and crawlspace air — with its dust and insulation fibres — directly into the system, bypassing the filter entirely. Sealing closes the route.

    This is the step people skip, and it is why cleaning "only worked for a month".

    Duct sealing & replacement →
  4. 4
    Filter

    Catch what does get in

    Now filtration works as intended, because the air reaching it is the air you meant it to treat. Sized with enough surface area that the system can still move air through it.

    Fourth, not first. A filter on a leaking system is treating a fraction of the air.

    Whole-home purification →
  5. 5
    Ventilate

    Stop it being there in the first place

    Filters do nothing about carbon dioxide, cooking emissions, humidity or off-gassing from furniture and finishes. Only replacing indoor air with outdoor air dilutes those.

    The step almost nobody is offered, and the reason filtration alone plateaus.

    Whole-home ventilation →
Why the order matters

What happens when you start at step four

This is the normal way it goes. Someone is worried about dust, or smoke, or a family member's breathing. They call a company, and a purifier gets fitted. It is the easiest thing in this whole silo to sell.

Then one of three things happens.

The dust comes back

Because the return ducts leak, and the system is pulling attic air in downstream of the filter. Much of what circulates never passes the filter at all. No purifier can fix a bypass.

The house still feels stale

Because filtration does nothing about carbon dioxide, humidity, cooking emissions or off-gassing. Those accumulate in a closed house, and only outdoor air dilutes them.

The system gets worse at its actual job

Because a dense filter in a slot never designed for it raises static pressure, costs capacity and stresses the blower. Air quality equipment can make heating and cooling measurably worse.

None of that means filtration is wrong. It means it is fourth. Do the first three and the same filter does far more, on a system that can actually move air through it.

Why this matters more here

Los Angeles has persistent regional particulate and ozone challenges, and during wildfire events fine particulate rises far above normal for days at a stretch. On those days there is nowhere else to go — the air inside your house is the only air you control.

What determines how your house performs on a bad air day is not the purifier. It is whether the envelope and ductwork are letting unfiltered outside air in, and whether the fresh air you do bring in arrives through a filter or through a gap.

Both of those are steps three and five. Which is exactly why we do not start at four.

From our knowledge base

Airflow and air quality are the same problem

Filtration only works if the system can move air through it. This is the measurement that tells you whether it can.

Why Is My House So Dusty Even After Cleaning?

Dust that returns within days is usually being pulled in through leaking ducts, not settling out of the room.

Read the article →

HRV vs ERV: Which One Makes Sense in a Dry Climate?

Most HRV vs ERV advice is written for Canada. The answer is different in a hot, dry climate — and so is the plumbing.

Read the article →

The 'Static Pressure' Secret: Why Your HVAC System is Suffocating

The most common reason an AC runs all day without cooling has nothing to do with refrigerant.

Read the article →
Common questions

Indoor Air Quality FAQs

What order should I do air quality improvements in?

Measure first, remove any genuine contamination, seal the ductwork, then filter, then ventilate. The order matters because each step makes the next one work. Filtration fitted to a leaking system is only ever treating a fraction of the air passing through.

Why will a good air filter not fix my air quality?

Because a filter only cleans air that reaches it. If your ducts draw unfiltered attic air in downstream, much of what circulates never passes the filter at all. And no filter addresses carbon dioxide, humidity or off-gassing, which need outdoor air.

Does indoor air quality actually matter in Los Angeles?

More than in many places. The region has persistent particulate and ozone challenges, and wildfire smoke events push fine particulate far above normal for days at a time. On those days, indoor air is the only air you have any control over.

What can I do about wildfire smoke getting into my house?

Filtration good enough to capture fine particulate, ducts sealed so unfiltered air is not being drawn in, and ideally a balanced ventilation system that filters incoming air rather than pulling it through gaps. Those three together do far more than a portable purifier.

Do air purifiers sold in California have to be certified?

Yes. California regulates ozone emissions from indoor air cleaning devices, and equipment sold or shipped into the state must be certified against that limit. Since October 2020 the rule has also covered in-duct electronic devices, which is exactly what a whole-home purifier is.

Do I have to do all five steps?

Not at all, and most homes do not need to. The point of measuring first is to find out which steps apply to you. Plenty of houses need only sealing, or only a better filter, and we would rather tell you that.

Is duct cleaning or duct sealing more important?

Sealing, in the great majority of homes we assess. Cleaning removes what is in the ducts today; sealing stops the mechanism that keeps putting it there. If dust returns within days of a cleaning, sealing is what you actually needed.

How much does an air quality assessment cost?

A fraction of the equipment it might save you buying, which is the honest argument for doing it first. You get the readings whether or not the findings lead to any work, and often the answer is cheaper than what you expected to spend.

Start at step one

Tell us what you are noticing and when it is worst. We will measure before recommending anything, and tell you which of the five steps you actually need.

Book an Assessment Call (555) 555-5555

Sources

The code requirements and thresholds on this page come from the following. All are public — check them yourself.