How to Clean and Restart Equipment After Wildfire Ash

Why this matters

After a wildfire passes near a neighborhood, the calls are mostly not about burned equipment. They are about equipment that survived and is now coated, clogged and partly full of fine ash: condensers that will not hold pressure in the heat, furnaces short-cycling on a blocked intake, pool pumps running against a packed filter, and a house full of the smell the system keeps redistributing. The instinct is to turn it on and see. That is the wrong order, because running equipment through ash pulls it deeper into coils, drains and ducts, and because the customer's insurance claim depends on a record of what was there before anyone touched it. This card walks the order, with one real job threaded through it.

The job. A single-story house about 2 miles outside a fire perimeter, ash fall about 1/4 inch on flat surfaces. Split system with a 90-plus percent gas furnace in the garage and a condenser on the side yard, plus a pool with a cartridge filter. The system ran for three days during the fire. The owners left during the evacuation and are back now. Pressure and static figures below are the readings from this job, offered to show the method; your equipment's limits come from its own data plate and manual.

Step 1: Confirm the house and utilities are safe to work at

Before any equipment: has the utility shut off or since restored gas or power, is the service drop or meter damaged, are there downed lines, and has the fire department or building official posted the property?

Why first. A gas service the utility shut off is restored by the utility, with its own leak check and relight. A burned or heat-damaged meter, service entrance or panel needs an electrician and often the utility before anything downstream is energized. Working on equipment at a house whose service is compromised puts the tech on a hazard no equipment step addresses.

On the job. Gas was never shut off; the meter and regulator are undamaged. The service drop is intact. No postings. Proceed.

Crew exposure. Ash and lingering smoke are a respiratory exposure for the crew from the moment they arrive. That belongs to the sibling FieldHealth card on wildfire smoke and outdoor work, including the respirator program and, in California, the state's wildfire smoke rule for outdoor workers. The short version for this job: respirators under the shop's 29 CFR 1910.134 program, gloves, eye protection and long sleeves, because wet ash is alkaline and can burn skin and eyes, and ash from burned structures can carry metals and asbestos.

Step 2: Document everything before you touch it

Photograph and note the condition of each piece of equipment as found, with time stamps, before any cleaning.

Why. Many homeowner policies cover smoke and ash damage, and the claim is easier when the condition before remediation is on record. Once the coil is rinsed and the filter is in the trash, the evidence is gone. The shop's job is the factual record; whether and how the policy pays is between the owner, their adjuster and, if it comes to that, their attorney.

On the job, the log as written:

ASH CONDITION LOG, before cleaning
0912  Condenser top grille: ash layer about 1/4 in
0914  Condenser coil face: gray, fins partly bridged
0920  Return filter 1 in: uniformly gray, bowed
0925  TESP with this filter: 0.92 in w.c.
0931  Condensate trap: gray sludge, slow drain
0936  Furnace intake terminal screen: half covered
0944  Pool cartridge filter: 8 psi over clean baseline
0950  Owner told: contact insurer before discard

Step 3: Isolate power before cleaning anything

Open the condenser disconnect and the furnace switch, lock and tag them, and prove dead on a known live source before and after, per NFPA 70E Article 120 (120.5 in the 2021 edition, renumbered in 2024), with work practices at 29 CFR 1910.333(b)(2). For pool equipment, open the breaker for the pump and any heater.

Why. The next steps put water and hands inside cabinets with capacitors and contactors. Ash is corrosive and, mixed with water, makes a conductive slurry. A unit cycling on while you rinse is the injury this step prevents.

What breaks if skipped. Beyond the shock, a condenser that starts mid-rinse with a fan blade turning is a laceration hazard and can throw slurry into your face.

Step 4: Get the dry ash off before anything gets wet

Remove loose ash from the condenser top, grille and base, the furnace intake terminal and the pool equipment pad with a HEPA vacuum or by misting lightly and wiping. Do not use a leaf blower or compressed air, and do not dry sweep.

Why. Blowing ash puts it back in the air the crew and neighbors breathe and drives it into the coil. Ash that is soaked before removal turns into a paste that packs into fins and drains.

On the job. The furnace's combustion air intake, a pipe terminal on the side wall, has its screen half covered with ash and debris. Clearing that screen is a combustion fix, not housekeeping: a restricted intake on a sealed-combustion furnace causes pressure switch trips and poor combustion.

Step 5: Clean the outdoor coil, inside out, at low pressure

With the fan guard removed, rinse the coil from the inside outward with a garden hose, not a pressure washer, and a coil cleaner the coil manufacturer permits. Keep water off the electrical compartment.

Why. Rinsing from outside in pushes ash deeper into the fin pack. A pressure washer flattens aluminum fins and turns a cleaning into a coil replacement.

Runoff. Ash rinse water is alkaline and may carry metals. Many jurisdictions ask that it not go to a storm drain. Direct it to a landscaped area away from the pool and any well, and follow local guidance where it exists.

On the job. The coil rinses mostly clean in about 20 minutes, with two passes at the bridged section.

Step 6: Clean the indoor side, starting with the filter

Replace the filter. Inspect the blower wheel, the indoor coil face and the drain pan, and clear the condensate trap and line. Look into the return plenum and the first few feet of return duct with a light.

Why. Three days of operation during the fire loaded the filter and pushed past it whatever it did not catch. The filter is the cheapest part on the system and the one restricting airflow the most right now.

On the job. With the gray filter, total external static pressure read 0.92 inches of water column against the 0.50 rated maximum on the furnace's data plate. With a new filter of the same type it reads 0.58, still above 0.50. The 0.34 difference between 0.92 and 0.58 was the filter. The remaining 0.08 over the rating suggests either the coil face is loaded or the duct system was over the rating before the fire; the coil face shows a light gray film. After a gentle cleaning of the coil face, static reads 0.53. The tech records that the system is 0.03 over its rated maximum and notes that the pre-fire static is unknown, so whether that last 0.03 is ash or the existing ductwork cannot be told from this visit.

The drain. The trap held gray sludge. Ash plus condensate forms a paste that blocks traps and overflows pans. Flush the trap and line until water runs clear, and check the float or overflow switch works.

Ducts. If the return or supply shows visible ash beyond the first few feet, or the house smells strongly of smoke with the system off, recommend a duct inspection and cleaning. NADCA's ACR standard, a voluntary industry standard that binds a contractor only where a contract or a specification adopts it, describes how that is done and verified.

Step 7: Clean the pool equipment before the pump runs long

Empty the skimmer and pump baskets, then clean the filter: hose a cartridge, backwash and recharge a DE filter, or backwash a sand filter. Test the water before chemical correction.

Why. Ash clogs the filter quickly and raises the water's pH and total alkalinity, and often its phosphate. A pump running against a packed filter overheats; chemicals added before the filter is clean are wasted.

On the job. The cartridge reads 8 psi over its clean baseline. After cleaning it returns to within 1 psi. The water test shows pH and total alkalinity up; the pool tech corrects over the next visit rather than in one dose.

Step 8: Restore power and restart, one system at a time

Remove locks and tags only after tools, guards and panels are back in place and everyone is clear. Close the disconnect standing to the side of it, not in front. Then run each system and verify the protective and combustion functions you disturbed, not just that it runs.

Why this step carries its own hazard. Re-energizing a cabinet that was wet an hour ago is where a fault you did not find shows itself. Water left in a contactor or in the electrical compartment is the risk; let it dry, and look before you close the switch.

On the job.

• Condenser. Fan rotates freely before power, starts normally, amps within the data plate range, pressures and temperatures normal for the conditions.
• Furnace. With a personal CO monitor on the tech, confirm the intake and exhaust terminals are clear, the pressure switch makes, the burner lights cleanly, and flue gas CO is within the manufacturer's range. Check ambient CO at the furnace and in the house.
• Air side. Supply-to-return temperature split normal, condensate running freely to its drain, static recorded at 0.53.
• Pool. Pump primes, filter pressure at baseline, GFCI protecting the equipment tested.

Step 9: Leave the customer a plan, not just an invoice

Ash keeps falling and keeps being tracked in for weeks after a fire.

Recommend: a filter check in 2 to 4 weeks, sooner if smoke returns; a re-rinse of the condenser after the next ash event; keeping windows and outside air intakes closed during smoke days; and the duct question if odor persists. Hand over the condition log from step 2 and the before and after readings, and tell the owner the shop will provide a written report to the adjuster on request.

What changes the answer. If the equipment was in the fire's heat zone rather than its ash zone (melted plastic, scorched wiring, a refrigerant line that got hot enough to discolor), stop cleaning: that equipment is a damage assessment and likely replacement, the refrigerant circuit may have vented or been overpressured, and the record should describe the damage rather than a cleaning.

References

• CDC and EPA guidance on cleaning up wildfire ash safely
• NFPA 70E Article 120 (120.5 in the 2021 edition, renumbered in 2024), and 29 CFR 1910.333(b)(2), de-energizing and verifying; 29 CFR 1910.134, respiratory protection
• NADCA ACR, Assessment, Cleaning and Restoration of HVAC Systems
• See related: Wildfire Smoke and Outdoor Work
• See related: How to Assess Equipment After Floodwater