Use a Range Hood CFM Calculator Before Buying

For a gas range, add the BTU ratings of every surface burner, then divide the total by 100. A rangetop with 18,000-, 15,000-, 12,000-, 10,000-, and 9,000-BTU burners totals 64,000 BTU, producing a baseline of 640 CFM.

For an electric or induction cooktop, use width rather than burner wattage: allow roughly 100 CFM for every 10 inches of cooktop width. A 30-inch model starts at 300 CFM; a 36-inch model starts at 360 CFM. Induction may put less waste heat into the room, but boiling, frying, and searing still create steam and grease-laden plumes that must be captured.

These figures are a starting target, not a sizing rule that overrides everything else. Increase the target when cooking regularly involves high-heat wok work, large stockpots, griddles, or several burners at once. A deep, wide hood can capture more effectively at a given airflow than a shallow hood with a larger CFM number.

Also avoid selecting a blower solely because it matches the calculation. Long duct runs, undersized ducting, multiple elbows, and restrictive roof caps reduce delivered airflow. The final hood must balance this appliance baseline with its capture area and the actual duct path.

The calculated figure is a baseline, not necessarily the purchase rating. Capacity should cover the most demanding cooking that occurs regularly: several burners running, a large pan searing, or a wok producing a fast plume of heat and grease.

For ordinary simmering, boiling, and occasional pan-frying, add roughly 15–25% above the starting target. For frequent high-heat cooking—wok work, blackening, repeated searing, griddling, or bacon and other greasy foods—allow 25–50%. This reserve lets the hood capture a burst at a usable speed instead of relying on its loudest setting.

Account for the room around the cooktop

An open-plan kitchen does not automatically require a huge CFM number, but it makes weak capture far more obvious. Once a plume escapes the hood edge, it can travel into living areas, where odor and fine grease linger on fabrics and surfaces.

For example, a 600-CFM baseline suits a typical cooking load; 700–750 CFM is a sensible everyday selection. A household that regularly stir-fries or sears multiple pans should instead consider 750–900 CFM, provided the hood is wide enough and the duct system can support it. More airflow cannot compensate for a shallow hood or a poor capture zone.

A blower’s published CFM is measured under controlled conditions. At the range, performance depends first on whether the hood can contain the rising plume long enough to pull it through the filters. A narrow hood over a wide cooktop lets steam, grease, and combustion byproducts spill around the sides before fan speed can matter.

For wall hoods, select a canopy at least as wide as the cooking surface; 3–6 inches wider on each side is preferable for gas ranges or frequent skillet cooking. Depth matters too: the front edge should cover the front burners rather than stopping well behind them. Island hoods need more overhang because cross-drafts can disrupt capture; matching ventilation to range size is therefore more important than simply buying a higher-CFM insert.

Mounting height changes the effective capture zone. A hood installed near the top of its permitted range needs more airflow and a deeper canopy than one mounted lower. Confirm the manufacturer’s height limits before finalizing the target CFM.

Ductwork then determines how much of that capacity survives installation. Use the manufacturer’s specified duct diameter—never reduce it to fit an existing run. Keep the path short and straight, minimize elbows, and use smooth metal duct rather than flexible corrugated pipe. Each sharp turn, long horizontal run, undersized roof cap, or restrictive wall termination adds static pressure and can make a powerful blower noisy but ineffective.

A hood rated at 600 CFM can create a serious pressure problem in a tight home. In many U.S. jurisdictions, kitchen exhaust above 400 CFM triggers makeup-air requirements; local code, climate, and the appliance instructions control the final rule. The makeup-air system must be interlocked so replacement air arrives when the hood runs, without backdrafting fireplaces, water heaters, or other combustion equipment.

Compare tested performance, not the box claim

Nameplate CFM is often a free-air or maximum-speed figure. Compare models using HVI-certified airflow and sound ratings at the intended duct configuration, then check the noise rating at the speed likely to be used daily. A hood that reaches its advertised airflow only on a 10-sone boost setting is unlikely to run long enough to capture a pan-searing session.

• Treat roughly 1–3 sones as a comfortable everyday range; higher settings are expected to be louder.
• Match the listed duct diameter exactly; reducing an 8-inch outlet to 6 inches adds resistance, noise, and lost airflow.
• Confirm that the electrician and HVAC contractor can provide the required interlock, tempered makeup air, and controls.

Treat recirculation as a compromise

Recirculating hoods pass air through grease and carbon filters, then return it to the room. They can reduce odors and airborne grease, but they do not remove heat, moisture, combustion byproducts, or cooking particles as reliably as ducted exhaust. They are best reserved for mild electric cooking where exterior ducting is impossible; frequent gas, wok, griddle, or high-heat cooking warrants a ducted canopy whenever feasible.