Energy Efficient Range Hood Installation: Placement and Ducting Glossary

Core Ducting Terms That Decide Efficiency

The duct run is the single biggest factor in how much air your range hood actually moves. A hood rated for 600 CFM can deliver less than half that if the duct is undersized, overly long, or full of bends. Understanding a few ducting terms before installation will save you from a noisy, inefficient setup.

Duct diameter is the internal width of the exhaust pipe, usually 6 or 8 inches for residential hoods. Larger diameters reduce air resistance, so an 8-inch duct moves more air at lower fan speed than a 6-inch duct with the same hood. Match the duct size to the hood's outlet collar, and never reduce the diameter mid-run.

Equivalent length is a way to count the extra resistance from elbows, transitions, and caps. Each 90-degree elbow adds roughly 10 to 15 feet of straight-duct resistance, and a roof cap adds about 30 feet. Keep the total equivalent length under 25 to 30 feet for best efficiency, and use long-radius elbows or 45-degree bends whenever possible.

• Duct diameter: internal width of the exhaust pipe; larger moves more air with less noise.
• Equivalent length: total resistance measured in feet, counting elbows and caps.
• Duct run: the actual path from hood to outside, including all fittings.

Placement Terms: Height, Clearance, and Capture

Where you mount the hood matters as much as the duct. The capture distance is the vertical gap between the cooktop and the hood's underside. Gas cooktops typically need 24 to 30 inches, while electric or induction can sit slightly lower at 20 to 24 inches. Too high, and steam and smoke drift past the intake; too low, and the hood blocks your view and may violate code.

The cooking surface width should be matched by the hood's width. A hood that is narrower than the cooktop cannot capture the outer burners' plumes. Ideally, the hood extends at least 3 inches beyond each side of the cooking surface. This overhang is called the capture area, and it is especially important for wall-mounted and island hoods.

For island hoods, the capture area is harder to achieve because air can flow around all sides. A taller or wider canopy compensates for the lack of a wall to contain the rising plume. If your island hood is more than 36 inches above the cooktop, expect reduced efficiency and consider a downdraft or stronger CFM model instead.

• Capture distance: vertical gap from cooktop to hood underside; follow manufacturer and code ranges.
• Capture area: the horizontal zone above the cooktop where the hood draws in air.
• Island hood: a ceiling-mounted hood with no wall behind it, requiring a wider canopy.

Venting Terms: Ducted, Ductless, and Dampers

A ducted hood vents air outside and is always more efficient at removing heat, moisture, and odors. A ductless hood recirculates air through charcoal filters, which adds resistance and requires regular filter changes. If you choose ductless, understand that efficiency drops, and the fan must work harder to move the same air.

A backdraft damper is a flap that closes when the fan is off, preventing outside air from entering. It also stops wind pressure from pushing air backward through the duct. Choose a damper that opens fully and smoothly; a sticky or undersized damper adds resistance and reduces airflow when the hood is on.

The vent cap at the exterior terminates the duct. A wall cap with a damper is common, but a roof cap with a larger opening allows freer airflow. Avoid screens or mesh on the cap that can clog with grease and lint; they force the fan to work harder and increase energy use over time.

Make-Up Air and Pressure Balance

Make-up air is the fresh air that replaces the air your hood exhausts. A powerful range hood can depressurize a tightly sealed home, pulling exhaust gases back down the flue or making doors hard to open. Building codes increasingly require make-up air for hoods rated above 400 CFM.

A make-up air damper opens automatically when the hood runs, allowing outdoor air in through a dedicated duct. This maintains pressure balance and keeps the hood working at full efficiency. Without it, the hood may underperform and create a safety hazard in homes with combustion appliances.

A passive vent or an active make-up air unit both work, but active units use a small fan and sensor to open only when needed. This avoids constant air leakage when the hood is off. Check your local code for CFM thresholds, and consult an HVAC professional if your hood is 600 CFM or higher.

Installation Quality Terms: Sealing and Insulation

A duct system is only as efficient as its seals. Every joint in the duct run should be sealed with aluminum foil tape or mastic, not standard duct tape which dries out. Leaks in the duct allow conditioned air to escape into attics or walls, wasting energy and reducing the hood's capture ability.

Insulated duct is a double-walled pipe with a layer of insulation between the inner and outer layers. It prevents condensation and heat loss in cold climates. Uninsulated duct in an attic can cause moisture buildup, which leads to mold and reduced airflow over time.

The transition from the hood's exhaust collar to the duct should be smooth and airtight. A crimped or crushed transition creates a bottleneck that increases noise and reduces flow. Use a metal transition piece and secure it with screws and foil tape to maintain the full diameter.

• Mastic or foil tape: proper sealants for duct joints; standard duct tape fails quickly.
• Insulated duct: prevents condensation and heat loss in unconditioned spaces.
• Transition piece: connects the hood outlet to the duct; must be smooth and full-diameter.