A dryer vent booster helps when the exhaust duct is longer than the appliance was designed for, which is common in apartments and converted spaces.
It is not a general purpose fan, though. Lint changes everything about how this installation has to be built and maintained.
Fit a dryer vent booster when the duct run exceeds the appliance maximum equivalent length, usually stated in the manual. Use a fan specifically rated for lint-laden air, control it with a pressure switch so it runs only when the dryer runs, and clean the whole duct at least annually.
Work out whether you need one
- Find the maximum equivalent duct length in the appliance manual.
- Measure the actual straight duct length.
- Add the equivalent length for each bend, often 1.5 to 3 metres per 90 degrees.
- Add the allowance for the wall cap or louvre.
- Compare the total against the appliance limit.
- Finally, check the duct is rigid metal rather than flexible foil.
A run that looks like six metres often measures fourteen once bends are counted properly.
Fix the cheap things first
Several problems look like a length issue and are not.
- Flexible foil duct restricts far more than rigid metal.
- A crushed section behind the appliance is extremely common.
- Lint accumulation reduces the effective duct diameter.
- A blocked or seized wall flap stops the air leaving.
- A clogged lint filter in the appliance restricts everything downstream.
- Finally, an animal nest in the duct is more common than people expect.
Clearing these often restores normal drying times without any fan at all.
Choosing the right dryer vent booster
A dryer vent booster is not the place for a general purpose inline fan.
| Requirement | Why it matters |
|---|---|
| Rated for lint-laden air | Ordinary fans clog and overheat |
| Accessible for cleaning | Lint will accumulate regardless |
| Pressure switch control | Runs only when the dryer runs |
| Metal construction | Fire safety in a lint environment |
| Appropriate airflow rating | Must exceed dryer requirement |
| Thermal protection | Lint restriction causes overheating |
Our metal duct fan range covers suitable inline units, and our duct fan comparison explains the types.
Control matters for safety
A dryer vent booster running when the dryer is off simply pulls conditioned air out of the house.
A pressure switch in the duct senses airflow from the dryer and starts the booster automatically. Meanwhile a current sensing relay on the appliance supply achieves the same result where duct access is awkward.
A permanently running booster wastes energy, cools the house and can affect combustion appliance draught. It also runs the fan through far more lint than necessary.
Installation points
- Fit the booster roughly midway along the run where possible.
- Keep at least 300 mm of straight duct either side.
- Use rigid metal duct with foil tape rather than screws at joints.
- Screws inside the duct catch lint and create a blockage point.
- Fit an accessible cleaning port near the booster.
- Finally, ensure the whole run remains accessible for annual cleaning.
The screw point matters more than it sounds. Fasteners poking into a dryer duct are a well-known lint trap, and they sit right where a booster makes airflow fastest.
Maintenance is not optional
Lint accumulation in a dryer duct is a recognised fire hazard, and a booster adds one more place for it to gather.
Clean the entire duct at least annually, and more often with heavy use. Meanwhile inspect the booster wheel itself, since lint on the blades unbalances it and reduces airflow.
For dryer venting requirements and safety guidance, NFPA publishes recommendations, and the appliance manual always takes precedence.
Dryer booster FAQ
How long can a dryer duct be?
It depends on the appliance, though many allow around 10 to 15 metres of equivalent length including bends. Check the manual rather than assuming a general figure.
Can I use a normal inline fan?
No. Ordinary fans are not rated for lint-laden air, and they clog, overheat and create a fire risk. Use a fan specifically designed for dryer duct service.
How do I switch the booster on automatically?
A duct pressure switch is the usual method, since it senses airflow from the dryer. A current sensing relay on the appliance supply also works well.
How often should I clean the duct?
At least annually, and more often with heavy use or a long run. Include the booster wheel, since lint on the blades reduces airflow and causes vibration.
A dryer vent booster solves a length problem safely, provided it is rated for lint, controlled by the dryer and cleaned every year. Fix the easy restrictions first.
Choose the right duct fan
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