Rotten-Egg or Sulfur Smell
Washington Gas says to leave the building immediately, avoid anything that can spark — including light switches and phones — and call 911, then the utility's emergency line from a safe place.
Free problem checker · Dulles, VA
Diagnose Your Air Duct and Dryer Vent Problem
Answer a few quick questions about what you're noticing. You'll get a report on the most likely causes, what to check yourself, when it's a safety issue, and which service fits — built on EPA, ENERGY STAR, U.S. Fire Administration and Virginia code guidance.
- Problem
- Questions
- Your home
- Report
Loading the problem checker. If it doesn't appear, the table below lists the same causes and next steps for each problem.
When a Duct or Vent Problem Is a Safety Issue
Three situations call for action before any diagnosis.
Hot-Plastic or Wiring Smell
Turn the system off at the thermostat, switch off its breaker if the smell continues, and have a licensed HVAC technician check it before running it again.
Hot Dryer or Burning Laundry Room
Stop using the dryer. The U.S. Fire Administration reports failure to clean was the leading factor in home dryer fires from 2018 to 2020, at 31 percent.
Common Duct and Vent Problems at a Glance
The same logic the checker uses, in one table. Start with the first check before paying for any service. Linked problems have a full post on the blog.
| What you notice | Most common causes | Check first | Related service |
|---|---|---|---|
| Dust blowing from vents | Clogged or loose filter; leaky return ducts; heavy debris in ducts | Replace the filter and check it fits without gaps | Dirty duct cleaning |
| Musty or moldy smell | Wet coil or clogged drain pan; humidity above 60% | Look at the drain pan; measure humidity | Duct mold remediation |
| Burning or strange smell | Dust burn-off; overheating electrical part; gas leak | Rotten eggs: leave and call 911. Hot plastic: turn the system off | Inspection after safety steps |
| Dryer takes too long | Lint in the exhaust duct; crushed or long duct; blocked outside cap | Check the outside flap opens while the dryer runs | Dryer vent cleaning |
| Rooms too hot or cold | Leaky, kinked or disconnected ducts; clogged filter | Compare register airflow room to room | Duct leak detection |
| Allergies worse indoors | Low-grade filter; pet dander in returns; dust in ducts | Upgrade and fit the filter; keep humidity at 30–50% | Cleaning for allergies |
| Noises or animals in vents | Rodents or insects; nest at an outside vent; loose ductwork | Note where the sound is; look for droppings or nesting | Nest and lint removal |
| Water or sweating ducts | Condensation on uninsulated ducts; clogged drain pan | Feel ducts for moisture while the AC runs | Duct repair |
| Dust after construction or cleaning | Construction dust in ducts; poorly contained cleaning | Look in register boots; replace the filter after 30 days | Post-construction cleaning |
What Fixing These Problems Usually Costs
Most problems on this page start with a check that costs nothing: the filter, the drain pan, the dryer's outdoor hood. When that doesn't end it, these are the Northern Virginia ranges for the work that usually follows.
- Camera inspection: $0–$125, often free with a booked cleaning
- Dryer vent cleaning: $135–$360
- Whole-system duct cleaning: $500–$800 per system
- Confirmed mold and mildew removal: $1,223–$3,757
Ranges reviewed in 2026, not a quote. Mold figure: Angi national cost data (2026).
How the Problem Checker Works
No sign-up, and nothing leaves your browser unless you choose to send the report.
Pick the Problem
Choose from nine problems homeowners report most: dust, smells, dryer trouble, comfort, allergies, noises, moisture and construction dust.
Answer Two or Three Questions
Each answer adds weight to the causes it points to, the way a technician narrows things down on a first visit.
Add Home Details
Home age, type and whether you rent change the advice — older heating systems, townhome dryer runs and landlord duties all matter.
Get Your Report
See the ranked causes, safety steps and home checks on screen, then email the report to yourself if you'd like a technician to follow up.
The checker gives general guidance based on your answers; it isn't a professional inspection. Sources: U.S. EPA; ENERGY STAR; U.S. Fire Administration; U.S. Consumer Product Safety Commission; EPA Indoor airPLUS; NADCA; 2021 Virginia Residential Code; Washington Gas; Code of Virginia § 55.1-1220. Reviewed September 25, 2026.
Common Problem FAQs
Why is dust coming out of my air vents?
The usual causes are a clogged or poorly fitting filter, leaky return ducts pulling in attic or crawl space dust, heavy debris inside the ducts, or construction dust after a renovation. Check and replace the filter first. If dust keeps blowing out after that, have the ducts inspected for leaks and buildup.
Why do my air vents smell musty?
A musty smell usually comes from moisture: a wet cooling coil, a clogged drain pan or line, or indoor humidity above 60 percent. The EPA recommends keeping humidity between 30 and 50 percent and keeping drain pans clean. If you see mold on the unit or ducts, turn the system off until it's inspected.
Why do I smell burning when the heat turns on?
A short dusty smell the first time the heat runs each season comes from dust burning off the heating equipment, and it fades within a day. A hot-plastic or burning-wire smell, or one that keeps returning, is different: turn the system off and have an HVAC technician check it. A rotten-egg smell means leave the home and call 911.
Why is one room hotter or colder than the rest of the house?
Leaky, crushed or disconnected ducts are a common cause, especially for rooms at the end of long runs through attics or crawl spaces. ENERGY STAR estimates a typical house loses 20 to 30 percent of duct air to leaks. Check that the register is open and unblocked, then have the ducts inspected.
Why is my dryer taking so long to dry clothes?
The vent is the usual cause. Lint builds up in the exhaust duct, the hose behind the dryer gets crushed, or the outdoor flap sticks shut, and moist air can't leave the drum. Run the dryer and check the outdoor flap: it should open and push out strong, warm air. The U.S. Fire Administration lists failure to clean as the leading factor in home dryer fires, at 31 percent from 2018 to 2020.
Is the problem checker free, and what happens to my answers?
Yes, it's free. Your answers stay in your browser while you use the checker. If you choose to send the report, we email a copy to you and send the report with your contact details to our inbox, and one local technician follows up. There's no mailing list.
Rather Talk It Through?
Describe the problem in your own words and a local technician will follow up.