Wildfire Smoke Indoors: When Should You Inspect Filters, Surfaces or Ductwork?

Where do you begin? With the filter. Wildfire smoke can cause serious issues in your home, especially if you live in an affected location. Smoke does not just vanish when the clouds clear. It leaves behind fine particles, soot, ash, and odor that settle indoors and get recirculated throughout your home by your heating and cooling system. For many, the stair solution is to have your ducts cleaned after wildfire smoke.

Smoke events are a part of the yearly cycle for homeowners in the Los Angeles and San Fernando Valley regions, including Tarzana, Calabasas, Glendale, Santa Clarita and Simi Valley. This guide describes what wildfire smoke leaves behind, the correct order to inspect, how to identify when your ducts need to be cleaned, and how to prepare your home in the interim for the next smoke event.

What Wildfire Smoke Leaves Behind Indoors

Smoke gets in your house through small spaces, doors, and your heating/cooling vents. Once smoke enters, it settles and leaves behind some things that can hang around for months:

• PM2.5: very small particles that get trapped in the lungs
• Soot and ash: Rough, abrasive particles and residue that collects on surfaces, filters, and the inner walls of ducts
• Smoke odor: Volatile compounds that cause an odor and get trapped in fabrics. These compounds get released by the fabrics when the HVAC system is turned on.

Wildfire smoke residue presents a problem unlike most other contaminants of dust that people encounter on a daily basis. Fine dust particles, particularly the particles that result from wildfires, are the primary source of the health concerns and removing and containing smoke residue indoors is as important as waiting for outdoor air quality to improve. These fine particles can sink deeply into fabrics and are extremely difficult to remove by typical dusting.

Unlike most dust, smoke residue remains deeply embedded in various fabrics and holds odors. Smoke residue and ash get carried by warm, moving air into the duct system, and accumulate in compartments, registers, and ducts, which can’t be accessed for cleaning. This can make a house look clean, but still result in a smokey smell. This smell is not on the surfaces of the house, but it is in the ducts and registers which carry air throughout the house.

The Right Order: Filter First, Surfaces, and Then Ducts

It is important to clean in the order of highest return on cost and effort.

1. Check and change the air filter.

Smoke particulate collects on air filters. It is the fastest, easiest, and most cost effective to change air filters first.

1. Dust and clean all surfaces.

Soot and odor can settle on surfaces.

1. Return-air grilles

Used to check if smoke traveled through ductways

While

1. Ductwork

Ash can travel through the ducts, where it can recirculate throughout the building.

Cleaning the ducts before changing a dirty filter, and stopping at a dirty filter to remove odor, is often a waste of money. The following steps help avoid both.

Begin with the HVAC Filter

The filter is the easiest and quickest component to check. Smoke can quickly load a filter with fine ash, slow airflow, and allow particles to pass through the system.

Filter checks and MERV ratings

• Check the filter and if it appears grey, ashy, or loaded, replace it.
• Replace the filter with a MERV 13 filter (or higher), if recommended and assuming your system can handle the increased pressure.
• Check and replace your filters more frequently for several weeks following the event, as ash takes time to settle.
• Have a filter on-hand for this smoke season to easily replace as needed.

Return-Air Considerations

Return-air grilles take air from your household, and if they have fine residue build up on them, smoke could have gotten into the ducts and was not just on the surface of the furniture. Clean the return-air grilles and see if the build-up returns. Return-air grilles themselves get dirty, so it is important to note if the build up returns, as it is a good indication that the ducts get dirty and need to be cleaned.

Surface and Soft Materials

Smoke residue shows up on every single surface and is easy to clean off hard surfaces. Soft surfaces will absorb the most odor, and it is easy for people to forget to clean them.

• Hard Surfaces: Regularly clean and wipe vertical and horizontal hard surfaces of your house, like walls, shelves, and floors, with appropriate cleaners. Avoid dry dusting, because it just kicks up the dust into the air.
• Soft Surfaces: Curtains, bedding, upholstery, and soft surfaces that can be washed should be washed regularly because they are big odor absorbers.
• Careful with Ventilating: Only open your windows and bring in fresh air when the outdoor air is improved and cleaner from a loss of traffic. You can check the air quality on AirNow.
• Top Down: The last thing you want is for settling dust to ruin the cleaning you did on your floors. Start cleaning high surfaces first, and then work your way down the cleaning ladder.

When Ductwork Needs Attention

Forgetting about ductwork is one of the characteristics of a modern homeowner. Ductwork is where the damage from trapped smoke remains and where smoke continually circulates throughout the house. There are a few ways to tell if smoke has reached the duct work: first, if the odor returns whenever the heating or air conditioning is turned on. Next, if there is soot or ash around the supply and return vents, and if fine grey residue reappears on surfaces after cleaning. Next, if your house still has a dusty or smoky smell and you have cleaned or changed the filters. Lastly, symptoms of allergies or other irritation in the house worsen.

The above symptoms indicate that cleaning your duct work would be worth the cost. Soot and ash build-up in the duct work. This ash and soot are circulated throughout the house. A technician can tell you how far the smoke traveled, which is practically impossible to tell from just the duct registers.

Why a filter change alone won’t solve your problem

A new filter traps new particles, but it is powerless against the soot on the walls of the ducts. When the fan turns on, it agitates the soot, and some of it gets blown back into your house. This is why you smell the same smoke when you turn on the AC or heater despite changing your filter. You’ll still smell smoke, no matter how many times you replace your filter because the source is downstream from the filter. You need to clean the ducts to get rid of the soot and particulates.

Smoke duct cleaning

When smoke soot settles in your ducts, it requires more than simply vacuuming your ducts. The cleaned ducts should be free from soot so the air that comes into your home is not contaminated with soot. This means the technician should inspect the runs, use negative pressure to suction the soot, clean the blower and coils, and remove obstructions.

Improving Indoor Air After Smoke

Cleaning up after a fire can be long and arduous. SSome measures remove what’s still there, while some offer protection for future events.

1. The first measure is good filtration. Either use higher rated filtration in the HVAC system or use a portable air cleaner with a HEPA filter.
2. The second measure is purification. Whole home systems may assist with persistent particles and odors from filters that have not been captured.
3. The third measure is balancing ventilation. Open windows to bring in clean outside air, if needed.
4. The fourth measure is testing to verify. If symptoms remain, or if the odor is still present, confirm with testing what is still in the air, rather than assuming what is safe.

Whole home solutions and testing can be found on their respective pages. The what is measured by an IAQ test page provides detail about the testing process.

When to Bring in a Professional

There are steps that can be taken as home owner measures, and then there are measures that should be taken by a professional. Call a professional when:

• Odor returns through the vent after cleaning.
• Visible soot is found in the ducts, or a heavy residue is found on registers.
• There are vulnerable individuals within the household, and the odor is not determined to be safe.
• The extent to which the smoke spread throughout the duct systems is not clear.

Our team can model, test, and conduct indoor air quality assessments and full duct cleanings. For the recommended maintenance interval of ducts, please see the recommendations for Southern California. Smoke is pulled in through return-air grilles and gaps in the home, where the fine soot and ash then settle and recirculate every time the system runs.

Prepare Your Home for the Next Smoke Event

Southern California’s prolonged smoke season means that there are many opportunities to prepare your home to improve the indoor air quality. Having high-grade filters on hand and scheduling duct cleanings after major smoke events are great long-term benefits to your indoor air quality. Prevention helps program your budget for furnishing your home rather than frequent deep cleanings to maintain indoor air quality. Call us and schedule a post smoke duct and IAQ inspection to confirm your system is clean and your family is able to breathe easy.

Frequently Asked Questions

1. Does wildfire smoke get into air ducts?

Return-air and gap openings in the home allow smoke to be drawn into HVAC systems, where soot and ash recirculate throughout the home.

2. Should I replace my HVAC filter after wildfire smoke?

Smoke loads a filter with fine ash quickly, restricting airflow and letting particles pass. Replace it when it looks grey.

3. How do I know if my ducts need cleaning after a fire?

If there is a smoke odor, soot is visibly returned and fine grey residue appears and cleans off quickly.

4. What MERV rating is best for wildfire smoke?

To capture fine smoke particles, most sources claim a MERV 13 rating would be appropriate. However, this requires that your HVAC system has the capability to manage the added resistance. Check your system specifications or consult with a service technician.

5. How do I improve indoor air after wildfire smoke?

Use a quality air filter or a HEPA portable air cleaner, clean all surfaces and materials (including soft surfaces), only ventilate when outdoor air is clean, and consider whole-home air purification to eliminate remaining particles.

6. Is it safe to clean smoke residue myself?

Cleaning hard surfaces and washing soft surfaces should be safe as long as you use proper cleaning supplies and do it with the necessary ventilation. It is best to not attempt to clean ducts or troubleshoot duct issues/core residue.

7. How soon after a smoke event should I inspect my home?

Check the air filter. Check your soft and hard surfaces. Inspect your ducts and do something about the smell/residue if you still have them. Don’t wait, hold off on cleaning the ducts because while you wait, everything circulates.