What the EPA says about air duct cleaning
The EPA’s page on duct cleaning says it “does not recommend that the air ducts be cleaned routinely, but only as needed,” and that cleaning “has never been shown to actually prevent health problems.” That settles it for a house with nothing visibly wrong.
We clean ducts and still give that answer first, because a cleaning sold to a house that does not need it is money spent on nothing. Our air duct cleaning page describes the visit and carries the posted price; this guide is about whether to book one.
The EPA page dates from 1997, was last updated in early 2026, and its position has not softened. Much of what duct cleaning ads promise, allergy relief among them, is exactly what the agency says has never been shown.
The three situations where air duct cleaning is worth it
The EPA names three conditions that justify a cleaning, visible mold, vermin and ducts clogged with debris, and each is something you can see or smell rather than something a salesperson has to tell you.
- Visible mold on the inside of sheet metal ducts. The agency’s wording is “substantial visible mold growth inside hard surface” ducts, with sheet metal as its example. Mold that returns after a cleaning means a moisture source, such as a wet crawl space, a sweating duct or a condensate leak, and that gets fixed first.
- Rodents or insects have been living in the ducts. The EPA’s phrase is “infested with vermin.” You know it from droppings in a register boot, nesting material, or a dead-mouse smell whenever the blower runs. Cleaning removes what they left behind; the entry point, such as a crawl space vent or a gap at the furnace plenum, gets closed too, or the problem repeats.
- The runs are packed with dust and debris. The third condition is ducts “clogged with excessive amounts of dust and debris,” and the practical test is dust coming out of the registers into the room. Causes include a remodel where drywall dust went down open floor registers, a return that never had a filter, or a house bought with decades of unknown history. Nearly half of Portland’s housing was built before 1960, so ductwork with decades of unknown history is a familiar find here.
Signs that point to the ducts, and signs that point somewhere else
Visible debris, mold or droppings point to the ducts; a first-heat smell, dust that returns overnight or a slow dryer point somewhere else. The table sorts each complaint by its usual cause.
| What you notice | What usually causes it | Will duct cleaning help? |
|---|---|---|
| A puff of dust from a register when the blower starts | Debris sitting in that run, often from construction or something dropped through the grille | Yes, if you can see the debris with a flashlight; otherwise a filter change comes first |
| A burnt, dusty smell the first time the heat runs each fall | Summer dust burning off the heat exchanger and blower | Rarely; it fades once the dust burns off, and our musty smell from the vents page covers what to check when it lingers |
| Dust back on the furniture a day after dusting | A low-grade filter, a filter that does not seal in its slot, or return leaks pulling air from a crawl space or attic | Not by itself; fix the filter and the leaks, then reassess |
| Black or green growth you can see on the duct wall or a register boot | Moisture in or around the duct | Yes, once the moisture source is found; moldy insulated duct may need replacing rather than cleaning |
| Droppings, nesting material or a dead-animal smell from a vent | Rodents in the ductwork or the crawl space | Yes, together with closing the entry point |
| Clothes take two cycles to dry and the laundry room runs warm | A lint-restricted dryer vent, not the HVAC ducts | Different service; see dryer takes too long to dry |
What a proper air duct cleaning involves
A real cleaning is source removal: everything loosened inside the ducts is pulled out of the house under negative pressure, not blown around and left to settle somewhere else.
The National Air Duct Cleaners Association, the trade body that publishes the industry’s cleaning standard, says source removal is the most effective method and that a system should not be considered cleaned if any dust or debris can still be seen at the visual inspection afterward. That is the bar to hold any company to, member or not.
- A look before any work. Registers come off, a flashlight or camera goes into the supply and return runs, and photos record what is there. If the runs are clean, the visit should end with a filter recommendation rather than a cleaning.
- Registers covered and an access port cut. Each register is sealed so the vacuum pulls through the ductwork instead of the rooms, and an access opening is cut into the supply trunk and another into the return trunk near the furnace.
- Negative pressure on the whole system. A truck-mounted or portable HEPA vacuum connects to the port and runs for the entire job, so anything loosened travels out of the house.
- Every run agitated toward the vacuum. Rotary brushes, air whips or compressed air lines work from each register back to the trunk, supplies and returns both. Skipping the returns is a shortcut to watch for.
- The trunks, the plenum and the blower compartment. The main lines get the same treatment, then the furnace cabinet around the blower is vacuumed. Cleaning the blower wheel and the coil themselves is a separate HVAC service.
- Close up and show the result. Access ports are sealed with metal plates, registers are washed and reinstalled, and you get after photos of the same spots as the before photos.
A chemical spray is a separate decision, not part of source removal. The EPA says no chemical biocides are registered for use in internally insulated ducts, and that sealants should never be applied over wet liner, active mold or debris.
What air duct cleaning costs in the Portland metro
The EPA puts duct cleaning services at $450 to $1,000 per heating and cooling system, and Portland quotes land in and around that band depending on how the job is priced.
Some companies price by the system and some by the register. A Portland cost calculator published in 2024 lists $35 to $45 per vent and $350 to $450 for a house with up to ten vents, rising with the count. National guides put a 2,000 square foot house at $300 to $700 (Fixr, 2026) and a typical job near $374 inside a $225 to $619 range (Thumbtack, 2026).
What moves the number is the register count, a second furnace or air handler, how reachable the trunks are, and whether the blower compartment and the dryer vent are included. Our price board posts a starting price for one system with a stated number of registers and lists what adds to it, so the quote is arithmetic rather than a negotiation at the door.
What to be wary of when a duct cleaning offer arrives
The National Air Duct Cleaners Association publishes a warning list for homeowners, and its pattern of pressure, cash and surprise problems is worth knowing before a mailer or online ad makes an offer.
- Pressure to decide on the spot, or a price that is only good today.
- A large payment up front, or cash only.
- “Unforeseen problems” discovered mid-job that raise the bill.
- Door-to-door selling.
- A whole-house price that is a small fraction of the ranges above. Fixr’s cost guide calls unusually low prices a red flag, and a low number can be the entry fee for add-ons.
Add two of our own. Mold announced from a flashlight glance, with no sample and no lab, is a sales line. And a whole-house cleaning finished in under an hour with a shop vacuum and no access port cleaned the first few feet behind each register, not the ducts.
Before anyone cuts into your trunk line, check the company out the way our contractor check guide describes, and ask to see the before photos while the registers are still off.
What to do instead when the ducts are clean
If the inspection shows clean runs, the money does more good on filtration, sealing and the dryer vent, the one run in the house where lint is a fire hazard.
- Change the furnace filter on the manual’s schedule and use the highest grade the manual allows; a filter more restrictive than the blower is built for strains the motor.
- Make sure the filter seals in its slot. A gap around it lets return air bypass the filter and carry dust straight to the supply side.
- Seal return leaks in the crawl space or basement with mastic. A return under negative pressure pulls in whatever surrounds it.
- Clean the dryer vent when it shows the signs of a clog. Lint in a dryer duct is a different kind of problem from dust in a supply run, and our dryer vent guide covers the signs and the cost.
The maintenance calendar gives the dryer vent its own check in May, after the spring chimney sweep and before the summer masonry window.
The short version
Book a duct cleaning when you can see mold, see or smell rodents, or see dust coming out of the registers, and skip it otherwise.
When you do book one, expect an inspection with photos first, negative pressure, every supply and return agitated, the blower compartment included, ports plated and after photos. Anything less is paying a cleaning price for a look.