The Brand and Model
How long you can extend your dryer vent hose safely depends on the type of dyer you own. You should refer to your specific model's owner's manual for recommendations on the maximum length of hose you can safely use. According to the Appliance 411 website, electric models made by General Electric are often able to handle a hose as long as 90 feet in some instances, while Whirlpool and Maytag dryers recommend a maximum of around 65 feet. Some brands like Amana and Camco suggest around 45 feet maximum.
Depends on the Vent Material
Vent hoses come in a variety of materials. The most common are rigid metal pipe, flexible metal pipe and flexible vinyl pipe. Rigid metal is the most effective vent and must be used to get the maximum extension length of your dryer because it offers less resistance to the exiting material. Flexible metal hoses are second best; vinyl is not generally recommended and should never be used on a gas dryer.
Depends on the Elbows
The best setup for maximum vent hose extension is the use of a straight piece of rigid metal pipe. Every elbow, or 90-degree bend, in the hose means the hose must be shorter from beginning to end. For example, the GE dryer that is rated for a 90-foot hose refers to a straight 90-foot piece of metal vent. The same dryer with one elbow in the pipe can only be 60-feet long or 45-feet with two elbows.
Depends on the Vent Hood
All dryer hoses must vent to the outside somehow. Different types of vent hoods are available. Some have an open hood about 4 inches wide, some are narrow and only around 2.5-inches wide and others have louvers that open with the force of the exiting air. The length of hose that can be used with each type varies. Generally louvered or wider hooded vents will allow you to extend the hose longer than the more narrow vent. Any type of vent hood that is more restrictive will vent less heat and moisture and therefore requires a shorter vent hose.