Range Hood CFM Calculator — Kitchen & Commercial Sizing

Enter the cooktop width, the kitchen's floor area and ceiling height, and pick the hood type. The calculator runs both residential methods at once — the 100 CFM per linear foot capture rule and the kitchen-area ACH method — and shows the larger result as the number to shop against, plus the duct size and the 400 CFM makeup-air flag. A 36-inch wall hood in a 144 sq ft kitchen lands at 300 CFM by capture and 324 CFM by ACH: buy the 400 CFM hood, not the 300.

The kitchen-size (ACH) method multiplies the room's volume by 15 air changes per hour and divides by 60: CFM = (area × ceiling height × 15) ÷ 60. A 12 × 12 ft kitchen with 9 ft ceilings holds 1,296 ft³, so 1,296 × 15 ÷ 60 = 324 CFM. This method sizes the room's general exhaust; the linear-foot method below sizes the hood's capture ability — use whichever result is larger.

Measure the cooking surface front-to-back or side-to-side in feet and multiply by 100 CFM for a wall-mounted hood, 120 for an island, or 150 for a pro-style range with high-BTU burners. A 36-inch (3 ft) wall cooktop therefore needs 300 CFM; the same cooktop on an island needs 360 CFM. This is the capture rule — it assumes the hood is the right width and hangs at the right height (24–30 in. above an electric cooktop, 27–36 in. above gas).

Commercial canopy hoods are sized by hood footprint, not cooktop width: 100 CFM per square foot of hood area for light-duty (electric) appliances and up to 150 CFM per square foot for heavy-duty gas ranges and broilers. A 10 ft × 3.5 ft canopy over a heavy-duty line is 35 sq ft × 100–150 = 3,500–5,250 CFM. Commercial exhaust also triggers fire suppression, grease ducts and makeup-air interlocks — this calculator sizes the airflow, and your local mechanical code governs the rest.

Two routes are accepted for canopy hoods: the footprint rule above, and the linear-foot rule for wall-mounted canopies — roughly 200–300 CFM per linear foot of heavy-duty cooking line. The exhaust must be balanced by makeup air of about 80–90% of the exhaust volume, or the kitchen goes negative and doors become hard to open. The dashboard's commercial panel computes the footprint band so you can bracket the spec before a kitchen designer quotes it.

600 CFM wants an 8-inch round duct at a working velocity near 1,720 FPM — inside the quiet 900–1,800 FPM band for short runs. If the run is longer than about 20 feet or has more than two elbows, step up to 10-inch, because every extra foot of duct adds back-pressure that a fixed-speed hood motor pays for in lost flow. A 6-inch duct on a 600 CFM hood pushes velocity past 3,000 FPM: loud in the kitchen and 15–25% flow loss at the hood.

Under IRC M1503.6, exhaust hoods rated over 400 CFM must be provided with makeup air — a motorized damper that admits replacement air, typically sized within 10% of the exhaust volume. The reason is depressurization: a 600 CFM hood in a tight, well-sealed home can pull the house several pascals negative, backdrafting atmospherically vented water heaters and furnaces and sucking wood smoke back down the fireplace. The calculator flags every result at or above 400 CFM.

Most residential hoods draw under 2 amps (a light load), but the standard installation practice — and many local codes — calls for a dedicated 15-amp, 120-volt circuit so the hood can never share a breaker with countertop appliances. Professional-grade 600+ CFM blower combinations, external inline blowers and makeup-air damper assemblies add another motor or two; plan one dedicated 15 A circuit for the hood and a second for the makeup-air damper if your installation needs one.

Outdoor grill hoods follow the pro-style math: 150 CFM per linear foot of grill is the floor, and open-air cross-breezes push real installs toward 200 CFM per linear foot. A common 42-inch (3.5 ft) built-in grill therefore wants 525–700 CFM. Depth matters more outdoors — a 24-inch-deep canopy covers the plume far better than an 18-inch one, and deeper hoods let you drop the mounting height into the 30–36 in. band where capture actually happens.

No — past roughly 400 CFM three costs stack up: makeup air becomes a code item, heating and cooling losses climb with every minute of runtime, and noise rises steeply (a 900 CFM hood on high can top 10 sones — conversation-stopping). The right answer is a hood sized to the cooktop with a variable-speed blower: run 250–350 CFM for weeknight cooking and reserve the top speed for searing and stir-frys.

The homepage calculator's Kitchen Hood preset is the quick version: 15 ACH applied to any room's volume with an 8-inch duct and safety-factor defaults. This page is the full hood-sizing decision: the linear-foot capture rule, the island and pro-style uplifts, commercial footprint sizing, the duct-size table, the 400 CFM makeup-air threshold and the dedicated-circuit question. Use the preset for a fast number; use this page when you are actually buying and installing the hood.