What Causes Poor Indoor Air Quality?

By Pacific Heating & Cooling | NATE-Certified Service Technicians | Updated April 2026

If dust settles on your furniture within a day of cleaning, the air smells musty, or your allergies feel worse inside than outside, your home may have an indoor air quality problem. Poor indoor air quality is most often caused by dirty air filters, dust and debris built up inside the ducts, leaky ductwork that pulls in unfiltered air, excess moisture from our marine climate, and weak ventilation that lets stale air sit. Below we walk you through each cause, what you can handle yourself, what needs a technician, and what it costs to fix across Western Washington.

The most common causes of poor indoor air quality

In most Western Washington homes, poor indoor air quality comes from five common sources: a dirty air filter, dust and pet hair inside the ducts, leaky ductwork, excess moisture, and poor ventilation. Usually more than one is at play, which is why a full check matters.

A dirty or clogged air filter

Your air filter is the first line of defense for the air in your home. Once it clogs, it stops trapping dust and starts restricting airflow, so more particles circulate through every room.

You will usually notice more dust than normal, weaker airflow from the vents, and a filter that looks gray when you pull it. Replacing the filter is one of the most common things our technicians do on a visit. During a seasonal maintenance visit, we check the filter and swap it for the right size and MERV rating for your system. If you want a stronger option, our team can walk you through an whole-home air filtration upgrade.

Dust and debris built up in the air ducts

Over the years, ducts collect dust, pet hair, and leftover construction debris. Every time your system runs, some of that recirculates into the air you breathe.

The signs are dust that returns fast, a musty smell when the heat or AC kicks on, and visible debris around the vents. Based on our service records, we completed 1,435 air duct cleaning jobs across Western Washington, most often in Tacoma, Puyallup, and Gig Harbor. When we clean, we clear the full duct system and wash the vent covers so you can see the difference.

Example From a Recent Service Visit
A homeowner in Puyallup told us dust kept settling on their furniture within a day of cleaning, and the air smelled musty whenever the system turned on. Our technicians found heavy dust and pet hair built up through the duct runs, along with debris left over from an older remodel.
Solution:
We cleaned the full duct system and washed the vent covers throughout the Puyallup home, then showed the homeowner before-and-after photos so they could see exactly what changed.

Torn insulation and a gapping seam on a crawlspace duct, one of the most common causes of dusty indoor air.

Leaky or poorly sealed ductwork

When duct joints leak, your system pulls in unfiltered air from the attic or crawl space instead of moving clean, conditioned air. In many older Western Washington homes, ducts run through those dusty, damp spaces.

You may notice uneven room temperatures, dusty air even with a clean filter, and higher energy bills. We test the ducts for leaks and handle professional duct sealing so your system moves the air you actually want.

Excess moisture and humidity

Our marine climate keeps outdoor humidity high for much of the year. When damp air lingers indoors, it can lead to mold, mildew, and that familiar musty smell.

Common signs are condensation on windows, a damp feeling in certain rooms, and stale odors that do not clear. A big part of moisture control is keeping the condensate drain clear so it does not back up and stay wet. Across our maintenance visits, treating the condensate drain to prevent buildup is one of the most common steps our technicians take. Its important to make sure your home is at the right indoor humidity level to stop musty odors and mold before they start.

Poor ventilation and stale air

Tighter, well-sealed homes hold in odors, cooking fumes, and stale air with nowhere to go. That traps the same air inside instead of refreshing it.

Stuffy rooms, lingering smells, and a stale feeling are the usual signals. We can assess how your home breathes and recommend filtration or fresh-air options that fit the way you live. No guesswork. No pressure. Just straightforward solutions.

What you can handle yourself vs. what needs a technician

You can improve your air quality on your own by changing filters on schedule, keeping vents unblocked, and running exhaust fans to move moisture out. Diagnosing duct leaks, deep-cleaning ducts, and correcting moisture problems calls for a technician with the right tools and testing.

What you can do yourself:

• Replace your air filter every 1 to 3 months, and sooner if you have pets.
• Keep supply and return vents open and free of furniture or rugs.
• Run bathroom and kitchen exhaust fans to pull moisture and odors outside.
• Vacuum the vent covers you can safely reach.

What our technicians handle:

• Testing ductwork for leaks and sealing them properly.
• Deep-cleaning the full duct system with professional equipment.
• Checking the condensate drain and overall moisture control.
• Recommending the right filter or filtration upgrade for your system.

We don’t just diagnose the issue. We help you understand it, so you know what is worth doing now and what can wait.

Signs you should call for an indoor air quality assessment

A few specific signs point to a problem worth having checked:

• Dust settles on surfaces within a day of cleaning.
• A musty or stale smell shows up when the heat or AC turns on.
• Allergy or asthma symptoms ease when you leave the house.
• You can see dust or debris blowing out of the vents.
• Windows fog up, or certain rooms feel damp.
• Airflow is uneven, with some rooms dustier or stuffier than others.

If two or more of these sound familiar, an assessment can pinpoint the cause. Our background-checked, NATE-certified technicians arrive in a 2-hour window and explain what they find in plain language.

What does improving indoor air quality cost in Western Washington?

Based on 1,435 duct cleaning jobs in our service records, costs ranged from $99 to $4,108, with a typical job around $775. A basic filter change is minor, duct sealing runs higher, and the final number depends on your home’s size, system access, and which services it needs.

Here is a quick look at what drives the range, using our real service data:

The spread comes down to a few things: how many vents your home has, whether your furnace sits in an attic or a crawl space, whether you add dryer vent cleaning, and whether the job includes sealing or filtration. Peace of Mind Club members receive duct cleaning at a reduced member rate. For larger projects like full duct sealing, flexible financing options are available.

Whatever the service, you get upfront pricing before any work begins, plus our 100% Money-Back Guarantee. Most duct cleanings are completed in a single visit.

Here is what Eric in Tacoma had to say:

“Tanner and team were quick and thorough. Great customer service. He educated me on everything and all transparent. Thank you guys!”

Eric in Tacoma

Still not sure what’s causing the problem?

Tell us what your system is doing and we’ll help you figure out the right next step. Pacific Heating & Cooling has been diagnosing heating and cooling problems across Tacoma and the South Sound since 1984. NATE-certified technicians, 2-hour arrival windows, and upfront pricing before any work begins.

If your home’s air does not feel as clean as it should, we can find out why. Our NATE-certified technicians will check your filters, ducts, and moisture control, then walk you through clear options with upfront pricing. Call Pacific Heating & Cooling at (253) 248-6260. No Surprises. Just Solutions.