Can a Gas Dryer Cause Carbon Monoxide?

Why a gas dryer produces carbon monoxide

A gas dryer heats air with a gas burner, then blows that air through the drum and out the vent. Burning gas produces carbon dioxide and water vapor, and some carbon monoxide, more if the burner is dirty, out of adjustment or short of air. The dryer is designed to send all of that exhaust, together with lint and moisture from the clothes, through the vent to the outdoors.

An electric dryer burns nothing, so it does not produce carbon monoxide. It still needs a clear vent for lint and moisture, but the CO question applies only to gas and propane dryers.

How exhaust ends up in the house

The danger comes when the exhaust cannot get out. The dryer's fan pushes the air, so a restricted vent raises the pressure behind the blockage, and exhaust leaks out at loose joints, around a disconnected duct, or back through the dryer. In a small laundry closet, a basement corner or an apartment with little ventilation, it accumulates quickly.

• Lint packed in the duct or at the outside hood
• A transition duct crushed behind the dryer when it was pushed back
• A duct that has come loose from the dryer or the wall
• An outside hood blocked by a bird nest, snow or ice
• A vent run far longer than the dryer maker allows
• A dryer vented into a crawlspace, attic or indoors

Warning signs

Some signs point to a vent that is not carrying exhaust away, which is the main risk factor for carbon monoxide from a dryer. Clothes that take longer and longer to dry, a laundry room that gets unusually hot and humid, a burning or exhaust smell during a cycle, and little or no airflow at the outside hood while the dryer runs all deserve attention. So does a CO alarm that sounds while the dryer is on.

Carbon monoxide itself has no smell or color, which is why an alarm matters. An alarm, or anyone feeling dizzy or sick, means everyone heads outdoors and someone phones 911 or the utility. Do not run the dryer again until the vent and appliance have been checked.

• Long drying times and a hot laundry room usually mean a restricted or clogged vent; have it cleaned and checked
• Weak or no air at the outside hood means a blockage or a crushed or loose duct; stop using the dryer until the run is inspected
• An exhaust or burning smell can mean exhaust is leaking or lint is overheating; turn the dryer off and call for service
• A CO alarm sounding with the dryer running means exhaust may be spilling indoors; leave and dial 911 or the utility

Venting rules that matter for gas

The dryer's installation manual sets the vent requirements: duct material, diameter, maximum length with deductions for each elbow, and the type of outside termination. For gas dryers these are not suggestions. The exhaust must go outdoors, never into a chimney flue, a crawlspace, an attic, a garage or the room, and indoor lint-trap kits sold for electric dryers are not for gas dryers. Rigid or semi-rigid metal duct is the usual requirement; plastic and thin foil ducts are not appropriate.

Local codes and building rules may add requirements, particularly in apartment buildings, so check the manual and with the building or local building department when a gas dryer is installed or moved.

What a dryer vent visit covers

A dryer vent cleaning starts at the dryer: it is pulled out, the gas line is left connected and undisturbed, and the transition duct is checked for crushing, foil or plastic material, and loose connections. The full run is then cleaned with rotary brushes and air from the dryer to the outside, and the hood is cleared and checked so its flap opens and closes freely.

Airflow at the termination is checked with the dryer running, and the run is compared to the dryer maker's length limits. Problems such as a duct that ends in the crawlspace, a run that is far too long, or screws that pierce the duct and catch lint are noted with the fix. Gas appliance repairs themselves go to a qualified gas technician.

Dryers in apartments and older homes

In older city buildings and converted houses, dryers are often squeezed into closets and kitchens with long, twisting duct runs to a wall or roof exit. Rooftop terminations collect lint and can be blocked by nests, and long runs exceed what the dryer maker allows. Shared vent systems in larger buildings have their own maintenance needs that the building manages.

If you rent and have a gas dryer, ask the owner or management who maintains the vent and when it was last cleaned, and make sure there is a working CO alarm in the apartment.

Keeping a gas dryer safe

Clean the lint screen before every load. Check the transition duct behind the dryer whenever the machine is moved, and make sure it is not crushed or kinked. Look at the outside hood during a cycle: the flap should open and air should flow strongly. Have the full vent run cleaned regularly; how often depends on use and vent length, and the dryer maker's guidance is a good starting point.

Have the dryer's burner and gas connection serviced by a qualified technician if it shows a yellow, lazy flame through the viewing port, makes unusual noises when igniting, or smells of gas. If you smell gas, leave without switching anything on or off and call the utility from outside.

Moving or replacing a gas dryer

Most crushed and disconnected ducts happen when a dryer is moved, replaced or pushed back after cleaning behind it. When a new gas dryer is installed, the vent should be inspected and cleaned at the same time, the transition duct replaced with the type the new dryer's manual allows, and the gas connection made by a qualified installer and checked for leaks. Leave enough space behind the dryer so the duct is not squeezed against the wall.

Where to put a CO alarm

Follow the alarm maker's instructions and your local rules for placement, and keep alarms near sleeping areas and on each level of the home. In homes with a gas dryer, an alarm on the same level as the laundry area adds warning close to the source. Test alarms monthly and replace them at the end of the life printed on the unit.