Ways to Deal with Dryer Exhaust

Introduction:

Exhaust systems for clothes dryers are often an afterthought in building construction. Being an MEP Engineering firm that has a lot of experience with these types of systems, we know that planning for dryer exhaust systems early in the design process can save money, help dryers function better and result in better space aesthetics.

Vented Dryers Require Exhaust to the Exterior:

1. The International Mechanical Code:

• • Exhaust duct shall be not less than 4-inch duct with smooth interior.
  • Ducts enclosed in a wall or ceiling cavity shall not be deformed (smashed to fit).
  • Transition ducts up to 8-feet are permitted and are not included in the permitted duct length calculation.
  • Maximum equivalent dryer duct length of 35-feet. Each 90-degree elbow is counted as 5-feet in the calculation. Each 45-degree bend is counted as 2.5-feet of dryer duct.
  • The maximum length of exhaust duct shall be determined by the manufacturer (i.e. long vent dryer models). Most jurisdictions will require that long vent dryer models be provided by the building owner in multi-unit buildings (the next tenant would not know that a long vent dryer model is required).
  • Dryer Exhaust Duct Power Ventilators (DEDPV) will be required for installations where the equivalent duct length exceeds code, and the manufacturer installation permitted lengths.
  • A label or tag is required within 6-feet of the dryer exhaust duct connection when the installed duct exceeds 35-equivalent feet.
  • Makeup air is required for dryers exhausting more than 200 cfm. Transfer grille will need to have an open area of 100 square inches (minimum). Makeup air is taken from the dwelling unit.

Methods to Provide a Better Installation:

1. Locate dryers near an exterior wall to avoid DEDPVs and long vent models.
2. Provide a 2×6 wall behind dryers.
3. Use a recessed dryer box for transition duct connection (replaces the first 90-degree elbow).

Less Common Dryer Exhaust Duct Methods:

1. Common exhaust duct in a shaft. The shaft shall be fire rated, code accepted exhaust duct penetrations, duct in shaft will be straight, only serve clothes dryers and have an exhaust fan at the top of the shaft. The exhaust fan will need to meet all of the code requirements (run continuously, be monitored remotely, be connected to a standby power source, etc.).
2. Ventless dryers (often called condensing) can be used without a dryer duct but will require a drain. Ventless dryers usually cost much more than a conventional vented dryer.

Conclusion:

At Royal Engineering we take pride in providing excellent MEP engineering plans. We can help keep projects running smoothly and more profitable by planning for dryer exhaust systems early on in a project. Our teams are trained to think through all parts of the design process, so that you don’t have to worry about your projects.