M1502. Flexible transition ducts used to connect the dryer to the exhaust duct system shall be limited to single lengths not to exceed 8 feet, and shall be listed and labeled in accordance with UL 2158A.
Flex lines on a dryer are not a good idea, especially on a gas one - they can and do restrict the air flow, collect lint, and pose a fire hazard. Use solid ductwork instead, and you'll shorten the drying time since the air will flow better, and help prevent lint buildup.
Codes and Standards
In the United States, most home inspectors refer to the International Residential Code (IRC) M1502 for dryer venting. However, some states may have additional regulations. The International Mechanical Code (IMC) 504 also includes extensive clothes dryer requirements.
Most standards call for clothes dryer vents to be no more than 25 feet in length, have few bends, and no kinks. Gas dryers, though, are often permitted to have ducts no longer than 35 feet in length. The more bends in the line that exist, the shorter the overall length should be.
The exhaust duct should be rigid metal 4 inches in diameter and no more than 35 feet in length or as specified by the duct manufacturer. This length should be decreased by 2.5 feet for every 45-degree bend the duct makes and 5 feet for every 90-degree bend the duct makes.
Some dryers can exhaust beyond 25 equivalent feet without a booster fan. Dryer Duct Booster Saves significant energy - reduces drying times 50% or more. Reduces lint build-up, dust & fire hazards by maintaining proper velocity in duct runs up to 150 equivalent feet.
PVC is plastic and not conducive for dryer vents. When lint travels through a PVC pipe, static electricity created by the plastic will pull the lint to the sides. Over times this causes a 4” pipe opening to shrink dramatically. This leads to poor airflow which creates drying exhaust issues.
In summary, while flexible accordion piping may seem like a convenient option for dryer venting, a hard pipe provides better airflow, fire safety, durability, and aesthetics. Investing in a hard pipe may cost a bit more upfront, but the long-term benefits make it a worthwhile investment for any homeowner.
How Long Should A Dryer Vent Be? A dryer vent should not exceed 35 feet in length. Furthermore, for every 45 degree turn of a dryer vent you should remove 2.5 feet in total allotted length. For every 90 degree turn, you should remove 5 feet in total allotted length.
Many building codes require dryer vents to be made of non-combustible materials such as aluminum or steel to reduce the risk of fire hazards. Semi-rigid ducts are often compliant with building codes when installed properly, as they are made of aluminum and offer heat resistance.
The most common place to vent your dryer is horizontally through the exterior wall near the dryer, which is the ideal placement. Other common locations are through (but not into) the basement or the attic/roof.
Measure and Mark the Hose and Vent
When you're shortening your dryer's flexible duct, remember to leave enough extra hose so you can reattach it before sliding the dryer back into place.
Rigid Metal Ducting: Rigid metal ducting, such as aluminum or galvanized steel, is widely considered the gold standard for dryer vent systems. These materials are non-combustible and can withstand high temperatures, reducing the risk of fires.
VIVOHOME 4 Inch 25 Feet Aluminum Flexible Dryer Vent Hose Air Ducting Non-Insulated with 2 Stainless Steel Clamps for HVAC Ventilation and Exhaust Pack of 1.
It should not be restricted. Dryer vents are often made from flexible plastic or metal duct, which may be easily kinked or crushed where they exit the dryer and enter the wall or floor. This is often a problem since dryers tend to be tucked away into small areas with little room to work.
M1502.
The passageway of dryer exhaust duct terminals shall be undiminished in size and shall provide an open area of not less than 12.5 square inches (8065 mm2).
Never install a dryer vent which has a bend greater than 90 degrees. Sharp bends restrict airflow and will lead to excessive lint buildup.
Termination of dryer venting must be to the exterior with a proper hood or roof cap equipped with a backdraft damper. Small orifice metal screening should not be part of the hood or roof cap as this will catch lint and block the opening in a very short time.
Rigid ducts are made from galvanized steel or aluminum. They can be either rectangular or cylindrical in shape. Rigid ducts are more durable than flexible ducts and can withstand extreme temperatures.
Venting a dryer through the roof is possible, but there are important considerations to remember. This method can be practical when sidewall venting isn't an option due to your building's layout. However, overall, sidewall venting is considered the safer option.
That penchant for static mixed with the hot lint that collects in dryer vents is a recipe for disaster. This could cause the lint ot build up and cause blockage as well. Third, using PVC to vent a dryer is a violation according to most residential building codes.
Excess condensation and damp clothes can be a sign you need insulation. While you don't have to insulate your dryer vents, it can help improve efficiency.
You'll want to decide between vent clamps or foil tape to secure the dryer venting to the dryer exhaust outlet and wall vent. If you're using a vent clamp to secure venting, place the vent clamp loosely on the edge of the vent hose and slide the edge of the vent hose over the wall outlet.