Range Hood CFM Calculator

Check range hood inputs

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Unit system:

Use US customary for common appliance specs, or Metric for room and duct dimensions.

Range and hood preset:

Pick the closest cooking setup, then edit the fields below to match the appliance manual.

Hood location:

Location changes the width-based CFM driver and capture warnings.

Vent route:

Use ducted outdoor exhaust for an actual ventilation CFM target.

Cooktop heat source:

The selected heat source changes whether total burner BTU is used in the target.

Hood width:

The hood should usually be at least as wide as the cooking surface, with island hoods often wider.

Cooking surface width:

This powers the hood-overhang check in the result table.

Total burner output:

Gas BTU sizing is compared with width and kitchen-volume drivers.

BTU/h

Kitchen floor length x width:

Open kitchens can justify a larger volume driver, but the appliance and hood capture still matter.

x {{ lengthUnit }}

Ceiling height:

Use the average height over the kitchen volume entered above.

Cooking intensity:

Higher heat, searing, wok cooking, and open plans push the volume driver upward.

Candidate hood rating:

Enter the hood model rating to compare headroom, duct velocity, and makeup-air trigger status.

CFM

Round duct diameter:

Smaller ducts raise velocity and can reduce installed performance or increase noise.

Makeup-air trigger:

Set the local trigger threshold before treating the warning as a permit decision.

CFM

Planned makeup air:

This does not size HVAC equipment; it flags the likely CFM shortfall above the trigger.

CFM

Buying reserve: {{ buying_reserve_percent }}%

Leave 0 for the base target; add headroom only when you deliberately want a stronger hood tier.

Duct run length:

Straight duct length from hood outlet to outdoor termination.

Duct elbows:

Count 90-degree elbows or equivalent fittings in the hood exhaust path.

Duct type:

Use the actual installed duct material and shape quality.

Minimum hood floor:

A minimum floor prevents tiny kitchens from recommending a token fan.

CFM

Driver	Value	Use	Copy
{{ row.driver }}	{{ row.value }}	{{ row.use }}

Hood rating	Fit	Headroom	Makeup-air flag	Copy
{{ row.rating }}	{{ row.fit }}	{{ row.headroom }}	{{ row.makeup }}

Check	Status	Detail	Copy
{{ row.check }}	{{ row.status }}	{{ row.detail }}

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Range hood sizing is an airflow and capture problem. The hood must move enough air to catch the cooking plume, carry heat and contaminants through the duct path, and avoid pulling the kitchen or combustion appliances into excessive negative pressure.

CFM demand depends on hood location, hood width, cooking-surface width, burner output, room volume, cooking intensity, duct size, and makeup-air requirements. A wall canopy over a modest cooktop, an island hood over a pro-style range, and a recirculating hood over induction are different design cases even when their nameplate widths look similar.

Range hood sizing diagram showing hood width, cooking plume, duct airflow, and makeup-air path

A ducted hood removes air from the building; a recirculating hood filters and returns room air. The CFM result is therefore a ventilation planning value, not a guarantee of capture efficiency, noise, code compliance, or appliance safety.

How to Use This Tool:

Choose the unit system and a range or hood preset. Presets fill common values, but every field can be adjusted for the actual installation.
Set hood location, vent route, fuel type, hood width, cooking-surface width, and total burner output when gas or professional gas is selected.
Enter kitchen dimensions and cooking intensity. The volume method uses the room size and air-change target as another CFM driver.
Enter the candidate hood rating, duct diameter, makeup-air trigger, and planned makeup-air capacity.
Use advanced fields for reserve, duct length, elbows, duct material, and minimum CFM floor when a route is long or a manufacturer requires a higher minimum.
Review Hood Sizing Table, Rating Ladder, Makeup Duct Checks, the CFM driver chart, the duct velocity chart, and the JSON export.

Interpreting Results:

Recommended CFM is the rounded planning airflow after the largest driver and reserve are applied. The largest driver may be hood width, burner BTU, room-volume exchange, or a minimum floor.

Candidate fit compares the entered hood rating with the recommendation. A hood can be short, borderline, sized, or materially oversized. Oversizing can trigger makeup-air requirements, higher noise, and more severe pressure imbalance.

Makeup-air shortfall appears when the recommended airflow is above the selected trigger and the planned replacement-air path is smaller than the modeled requirement. In many residential codes, high-capacity kitchen exhaust can require a dedicated makeup-air system.

Duct velocity and recommended round duct are duct checks. A small duct can raise velocity, noise, static pressure, and delivered-airflow loss even if the hood nameplate CFM looks adequate.

Technical Details:

The model calculates separate airflow drivers, then selects the largest. Wall hoods use a lower width-based rate than island or downdraft configurations because island plumes are more exposed to cross-drafts and lack a back wall to help capture. Gas and professional-gas cases also include a BTU-based driver.

Formula Core:

\begin{array}{lcl} Q_{width} & = & \frac{W_{hood}}{12} \times R_{location} \\ Q_{BTU} & = & \frac{burner BTU per hour}{100} \\ Q_{volume} & = & \frac{L \times D \times H \times ACH}{60} \\ Q_{base} & = & \max (Q_{width}, Q_{BTU}, Q_{volume}, Q_{minimum}) \\ Q_{rec} & = & round up to 25 CFM (Q_{base} \times (1 + r)) \end{array}

Rlocation is 100 CFM per linear foot for wall or under-cabinet hoods and 150 CFM per linear foot for island or downdraft cases. Metric dimensions are converted to feet before the calculation.

\begin{array}{lcl} Duct velocity & = & \frac{Q_{candidate}}{π \times {(\frac{d}{24})}^{2}} \\ Equivalent length & = & (straight run + 5 \times elbows) \times duct multiplier \\ Makeup-air need & = & \max (0, Q_{rec} - trigger) \end{array}

Range hood sizing drivers
Driver	Modeled role	Practical check
Width	Applies location-specific CFM per linear foot of hood width.	Island hoods usually need more width and airflow than wall hoods.
BTU	Uses total gas burner output divided by `100`.	Follow the appliance manufacturer when it requires a higher value.
Room volume	Uses kitchen volume and selected air changes per hour.	Open plans may need judgment about what volume is actually connected.
Duct	Checks round-duct velocity and equivalent length.	Small, flexible, or long ducts can reduce delivered CFM.
Makeup air	Flags replacement-air capacity above the selected trigger.	Coordinate with code, combustion safety, and HVAC design.

Worked substitution: a 42 in wall hood over a 60,000 BTU/h pro-style gas range has a width driver of 350 CFM and a BTU driver of 600 CFM. A 14 ft x 14 ft x 9 ft kitchen at 20 ACH adds a volume driver near 588 CFM. The rounded recommendation is 600 CFM.

Accuracy Notes:

Hood capture depends on mounting height, hood depth, side panels, burner position, cooking style, cross-drafts, and filter condition.
Nameplate CFM can differ from installed airflow after duct losses. Use certified ratings and manufacturer duct tables when available.
Makeup-air rules vary by jurisdiction and fuel-burning appliance configuration. Confirm local code before installing high-capacity exhaust.
Recirculating hoods can reduce some grease and odor but do not remove moisture, combustion products, or heat from the building.
Combustion safety, backdrafting, and pressure balancing should be checked by qualified professionals when gas appliances and large exhaust fans share the building.

Worked Examples:

Pro-style gas range. A 36 in gas range with 60,000 BTU/h under a 42 in wall hood produces a 600 CFM recommendation. If the makeup-air trigger is 400 CFM and no replacement-air system is planned, the shortfall is about 200 CFM.

Island cooktop. A 36 in island hood uses the higher width rate, so width alone points to about 450 CFM before reserve. Cross-drafts and wider overhang are often more important than a wall-mounted case.

Small induction cooktop. A 30 in induction setup with light cooking may be governed by width and minimum-CFM checks rather than BTU. Duct route and noise may matter more than simply picking the largest blower.

FAQ:

Why can a larger hood create a makeup-air issue?

A large exhaust fan removes indoor air quickly. Without replacement air, the building can depressurize, doors can become harder to open, and combustion appliances may backdraft.

Is the BTU rule enough for every gas range?

No. It is a planning rule. Manufacturer installation instructions, hood geometry, cooking style, and local code can require a different airflow or duct design.

Why does duct diameter affect the result?

The same CFM through a smaller duct moves faster. Higher velocity can increase noise and static pressure, and the hood may deliver less real airflow than expected.

Does a recirculating hood need the same CFM?

It can still need capture airflow at the hood, but it does not exhaust air outdoors. Treat its result as a capture comparison, not as whole-kitchen ventilation.

Glossary:

CFM: Cubic feet per minute, the airflow rate commonly used for residential range hoods.
Capture: The hood's ability to collect the cooking plume before it spreads into the room.
Makeup air: Replacement air supplied to offset air removed by exhaust equipment.
Equivalent duct length: A duct-run estimate that adds penalties for elbows and material resistance.
Recirculating hood: A hood that filters air and returns it to the room instead of exhausting outdoors.

References:

How Much Ventilation Do I Need?, Home Ventilating Institute.
Chapter 15 Exhaust Systems, Section M1503.6 Makeup Air Required, ICC code publication.
Residential Ventilating Fans, ENERGY STAR.