The Ducts Nobody Cleans: Dryer Vents, Range Hoods, and Bath Fans

Every house has three small exhaust systems that nobody thinks of as systems: the dryer vent, the range hood and the bathroom fans. They are installed once, wired to a switch, and then expected to work forever while moving lint, grease and moisture through ducts nobody ever opens.

They are worth a paragraph in any maintenance routine for two reasons. One is safety - the dryer vent is a genuine fire risk when it is neglected. The other is moisture - a bath fan that discharges into an attic instead of outdoors puts water where the house least wants it. This piece extends the Claremont home maintenance guide into the ductwork owners never see.

The dryer vent, first, because it matters most

A clothes dryer moves hot, humid air loaded with fine lint. The lint trap catches most of it. The rest travels down the duct, and where the duct is long, kinked, ridged or restricted, that lint settles and accumulates.

The consequences arrive in order. First the dryer takes longer, because it cannot exhaust properly. Then it runs hotter. Then, in the worst case, accumulated lint in a hot duct becomes a fire.

The signs are easy to read once you know them. Clothes needing more than one cycle. The laundry room getting noticeably hot and humid during a run. A burning or hot-lint smell. Little or no air felt at the exterior vent hood while the dryer runs. A vent flap that no longer opens.

The habits are equally simple. Clean the lint screen every load. Look at the exterior hood periodically to confirm the flap opens and is not blocked by paint, screen mesh or a bird nest. Have the full duct run cleaned as a routine item, and more often for a long run or a household that does a lot of laundry.

Dryer duct construction, and the common defects

Two defects show up repeatedly in older houses. The first is FLEXIBLE PLASTIC or thin foil duct, which sags, kinks, tears and traps lint in its ridges. Rigid or semi-rigid metal duct is the right material, and if you find plastic behind a dryer that is a finding worth acting on.

The second is a duct that runs too far, turns too often, or terminates somewhere it should not. A dryer vent must discharge outdoors - never into a crawl space, an attic, a garage or a wall cavity. Screens on the exterior termination catch lint and defeat the vent; the hood should have a flap, not mesh.

Gas dryers add a combustion component, and any concern about the gas connection, the appliance itself or its venting belongs to a licensed plumber or appliance technician rather than to a homeowner with a flashlight. Anything touching gas gets routed to a licensed trade, without exception.

Range hoods, and the recirculating problem

Kitchen hoods come in two kinds and people rarely know which they have. A DUCTED hood carries grease, moisture and combustion by-products outdoors. A RECIRCULATING hood pulls air through a filter and blows it back into the kitchen, which removes some grease and odor and removes no moisture and no combustion products at all.

If your hood has no visible duct and there is no exterior termination above the kitchen, you almost certainly have a recirculating unit. That is a legitimate configuration in many houses, but it is worth knowing, because it changes how you ventilate while cooking.

Maintenance on a ducted hood is mostly grease. Metal filters are dishwasher-friendly and should be cleaned regularly; charcoal filters in recirculating units are replaced rather than cleaned. Grease that gets past the filter coats the duct, and a greasy duct is both a fire concern and a performance problem.

Check the exterior termination for the same failures as the dryer: a flap that will not open, paint sealing it shut, mesh clogged with grease, or a nest.

Bath fans, and the moisture question

A bathroom fan exists to remove moisture, and the single most common defect is a fan that discharges into the attic rather than outdoors. That configuration takes every shower's worth of humidity and delivers it to the coldest surface in the building, which is how a dry-climate house grows a moisture problem nobody can explain.

Look, or have someone look, at where the duct actually goes. It should run to a dedicated exterior termination - a roof jack or wall cap - not simply end above the ceiling. While you are up there, the same trip answers the attic ventilation questions in the insulation guide, because these systems share a space and interfere with each other.

The other bath fan issues are ordinary. Dust-loaded blades and grilles lose most of their capacity, and cleaning them restores it. A fan that is loud but moves little air is often disconnected, crushed, or venting into a long flexible run with too many bends. A fan that runs for a couple of minutes is not doing much; the useful habit is to run it during the shower and for a stretch afterward, which timers and humidity sensors handle without anyone remembering.

Makeup air, briefly

Every exhaust fan removes air from the house, and that air has to be replaced from somewhere. In a tight house with powerful exhaust, that replacement can be drawn down a flue, which is the mechanism behind backdrafting.

This is not a reason to avoid ventilation. It is a reason to treat any combustion appliance - furnace, water heater, gas dryer, fireplace - as part of the same conversation. Odd smells, soot, or a pilot that goes out when a fan runs are signals to stop and bring in a licensed professional. Fireplace and flue specifics live in the chimney and fireplace guide.

Who does what

Cleaning lint screens, washing hood filters, vacuuming fan grilles, and checking exterior terminations from the ground are owner tasks. Full duct cleaning, re-routing a duct, replacing plastic dryer duct with metal, and correcting a fan that vents into an attic are contractor work. Wiring and fan replacement go to a licensed electrician. Anything gas-related goes to a licensed plumber or gas fitter, and where work involves new penetrations through the roof or wall, ask the City of Claremont about permits.

The bottom line

These three systems are cheap to maintain and expensive to ignore. Clean the lint every load and the duct on a routine. Find out whether your range hood is actually ducted. Confirm your bath fans discharge outdoors rather than into the attic. And treat any exterior termination that will not open as a blocked system rather than a cosmetic detail.

The wider routine sits in the owner's guide. This is general information rather than a mechanical or electrical opinion; a licensed professional evaluating your actual installation governs. Anthony Grynchal has been licensed in California since November 2009.