In-Line Fans

In-line fans are remote fans which can provide ventilation or boost airflow with little detectable noise. They provide a solution to noisy or ineffective bathroom fans, ineffective dryer exhaust, and recirculating range hoods.

Simple single-port or versatile multi-port in-line fans can be used to supply ventilation for most single-family residential applications. A multi-port design allows one fan to provide ventilation for multiple rooms, such as two bathrooms and a laundry. Depending on the configuration, control switches can be manual or automatic.

Because in-line fans are located remotely, there is little noise detectable at intake and exhaust ducts. Rather, the noise occurs outside of conventional living spaces, within attics or other buffered spaces.

Some common uses for in-line fans include:

• General ventilation: An in-line fan can be used in a whole-house, exhaust-only or supply-only ventilation scheme, depending on the climate (exhaust-only is not recommended in hot humid climates, supply-only is not recommended in cold climates). In an exhaust-only system, exhaust ports are placed in bathrooms, laundries, or other areas, and connected together through the in-line fan, typically placed in the attic. Supply ports in a supply-only system must be strategically placed so that occupants are not made uncomfortable from the incoming, unconditioned air (alternately, air can be supplied to the return of a central HVAC system in most climates).
• Bathroom Exhaust: If fan noise is a problem, an in-line fan placed in the attic will operate much more quietly than a typical fan located in a bathroom ceiling. In layouts where bathrooms adjoin or are in close proximity on the same floor, it may be cost effective to use a single in-line fan with ducts connecting to each room. If ductwork is too long for effective moisture or odor exhaust, an in-line fan may augment flow capacity. It should be noted that excessive noise from bathroom fans is often the result of the fan (fans are available with low sound output, or “sone” ratings) or poor installation and duct sealing. Therefore, if an in-line fan is being considered to reduce fan noise, other causes of excessive noise should be investigated before selecting an in-line unit.
• Dryer Vent Boosting: In larger homes or multi-family units, dryers must often be installed far from exterior vent outlets, requiring duct lengths that exceed manufacturer's recommendations, compromising dryer efficiency, and allowing hazardous heat build-up. Some in-line booster fans are specially designed to maintain safe and effective dryer operation.
• Indoor Air Quality, Fresh Air Injection, Building Pressurization: Buildings which are highly insulated and tightly sealed may require mechanical introduction of fresh air for proper ventilation and pressurization. In-line fans can be used in conjunction with HVAC systems for air supply, air purification, dehumidification, or heat recovery.
• Duct Boosting for Remodeling or Retrofit: When an existing HVAC system is used to heat or cool an addition, new duct runs may stretch too far from the air handler. In-lines fans can increase flow to remote areas and help balance the air supply throughout the system.
• Radon Mitigation: Vent lines placed below slabs for radon mitigation may require an in-line fan to exhaust radon gas.

Note that exhaust-only fans can depressurize a building and draw air into the home. The process, called backdrafting, could lead to dangerous concentrations of lethal exhaust gasses being drawn into the home. Providing an alternative source of make-up air using passive air inlets or balanced exhaust systems can alleviate this threat. Carbon monoxide detectors can serve as an early warning device for backdrafting, and the use of sealed combustion appliances can also eliminate backdrafting concerns.

	In-line ventilation fans can improve the air quality within a home, by exhausting fumes and odors.

Initial Cost  

More than conventional fans. In-line fans start at about $150 and range up to $700.

Operational Cost  

The cost to operate an in-line fan will vary depending on size and efficiency of the fan. ENERGY STAR rated fans are available that will use less energy for the same amount of ventilation than non-ENERGY STAR units.

Use of in-line fans must conform to applicable code requirements for ventilation, HVAC equipment, and electrical installations.

Not Applicable

Manufacturers usually provide installation instructions to help minimize operational or acoustic problems. Generally, setting up the unit is not too difficult. The fans may be placed almost anywhere. Closets, chases, wall cavities (if wide enough), basements, spaces between floors, and attics are common locations. In-line fans should be located in the duct run near the primary exhaust port. This improves performance and reduces noise. Suspension attachments and other approaches can be used to reduce vibrational, structure-borne noise. Externally insulated ductwork can muffle airborne noise and diminish the likelihood of condensation within the duct. Condensation can damage ductwork, fan motor, and indoor air quality. Some fans installed on a horizontal axis require additional fitting with a condensate drain line to remove the water before it can harm the motor.

Ductwork is a key element in proper delivery of the air supply and must be appropriately sized. For multi-port systems, equivalent grille pressures may be difficult to obtain from ducts that are not all the same length. Remote, in-line ventilation systems therefore commonly use flex-duct despite its high airflow resistance because it can be easily routed to intake and exhaust grilles. Backdraft dampers prevent airflow from moving the wrong way in ducts when the fan is not operating, and may be required, depending on the application.

Because of concerns about pressurization and backdrafting described above, it is recommended that overall ventilation needs and requirements be evaluated by a competent HVAC contractor or consultant before installing in-line fans or other mechanical ventilation equipment.

Typical ventilation fan warranties apply to in-line fans. A one-year parts and labor warranty is typical.

Remote, in-line units are quiet, ventilate well, use little energy, and tend to be maintenance-free if properly installed.