Range Hood CFM Calculator

Check range hood inputs

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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:

Use the unit on the hood spec or tape measure; changing the selector preserves the same hood width.

Cooking surface width:

Use the source unit for the burner or element width; changing units converts the displayed width.

Total burner output:

Enter BTU/h from the appliance spec, or kW when that is the published burner output.

Kitchen floor length x width:

Length and width share one floor-dimension unit; changing it converts both displayed values.

Ceiling height:

Use the average height over the kitchen volume; the selected unit belongs only to this field.

Cooking intensity:

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

Candidate hood rating:

Enter the hood model rating in the unit printed on the product spec; results normalize it to CFM and m3/h.

Round duct diameter:

Use the round-equivalent duct size and the unit from the duct or hood manual.

Makeup-air trigger:

Set the local trigger threshold in the unit used by your code note or permit worksheet.

Planned makeup air:

Use the planned makeup-air capacity unit from the damper, fan, or HVAC design note.

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, in the selected source unit.

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; choose the unit used by your baseline rule.

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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Kitchen ventilation is a capture problem before it is an airflow number. The hood has to intercept hot air, grease mist, steam, odors, and gas-combustion byproducts while the plume is still concentrated above the cooking surface. Once that plume spreads into the room, a larger fan rating cannot fully make up for poor capture shape, weak overhang, cross-drafts, or a restrictive duct route.

CFM means cubic feet per minute, the airflow rate commonly printed on residential range hoods. More CFM can help with heavy searing, wok cooking, or a high-output gas range, but it also pulls more conditioned air out of the house. A quiet wall canopy with enough width and a short smooth duct can perform better in real cooking than a narrow high-CFM hood connected to undersized ductwork.

Capture area comes from hood width, depth, mounting height, and whether the cooktop is against a wall or on an island.
Plume load comes from burner output, cooking style, cookware, and the amount of smoke, steam, and grease released at once.
Delivered airflow depends on duct diameter, duct length, fittings, outlet restrictions, and whether the hood rating is certified under a comparable test.
Replacement air matters when exhaust capacity is high enough to depressurize a tight home or disturb naturally drafted combustion appliances.

Diagram of a range hood, cooktop plume, exhaust duct, capture zone, and makeup air path

Hood location changes the sizing judgment. A wall or under-cabinet hood gets help from the wall behind the range, while an island hood has to capture an exposed plume. Downdraft systems pull sideways or downward against natural buoyancy, so the appliance manufacturer's guidance carries more weight than a simple CFM rule. Ducted hoods remove air outdoors; recirculating hoods filter and return air to the kitchen, which means they do not remove moisture, heat, or combustion products from the building.

Replacement air is the hidden constraint in many high-CFM plans. When a fan removes several hundred CFM from a tight home, air has to enter from somewhere. Without a planned makeup-air path, the house can depressurize, doors can pull harder, fireplaces can spill smoke, and naturally drafted combustion appliances can backdraft. Many residential code references use 400 CFM as a makeup-air trigger, but local amendments, appliance instructions, and combustion-safety details can be stricter.

Range hood planning factors
Planning factor	Why it changes CFM	Common mistake
Hood width and location	Wider hoods and exposed island plumes need more capture area and airflow.	Choosing only by cabinet opening, not by the cooking surface and plume path.
Gas burner output	Higher BTU/h burners create more heat and combustion products.	Ignoring the range manual when a pro-style appliance calls for a larger hood.
Kitchen volume	Large and open kitchens may need more air movement to clear smoke and odor.	Using the whole floor plan when only the active cooking area is relevant.
Duct size and route	Small, rough, or long ducts raise velocity and pressure loss.	Treating nameplate CFM as delivered airflow after installation.
Makeup air	Large exhaust fans may require deliberate replacement air.	Buying a high-CFM hood before checking local code and combustion safety.

A range hood CFM estimate is best read as a planning target for selecting a model and checking the installation path. Final sizing still depends on the hood manual, mounting height, duct limits, local code, and whether gas appliances share the same pressure zone as the kitchen exhaust.

How to Use This Tool:

Start with the preset that resembles the installation, then replace the preset values with the appliance and duct details you actually plan to use.

Choose Range and hood preset, then use each measurement's unit selector to match the appliance spec, tape measure, duct manual, or code note. The preset fills a complete example, and changed setup fields switch the plan to Custom range hood plan.
Set Hood location, Vent route, and Cooktop heat source. Gas and professional gas selections add the Total burner output field because BTU/h becomes one of the CFM drivers.
Enter Hood width and Cooking surface width. Compare these with the capture-width warning later, especially for island hoods that often need extra overhang.
Fill in Kitchen floor length x width, Ceiling height, and Cooking intensity. These values set the kitchen-volume air-change driver used alongside width and BTU.
Add the Candidate hood rating, Round duct diameter, Makeup-air trigger, and Planned makeup air. The summary badges flag candidate fit, makeup-air status, and duct status as soon as the inputs are valid.
Open Advanced when the route is unusual. Buying reserve, Duct run length, Duct elbows, Duct type, and Minimum hood floor refine headroom and duct-route checks.
If the red Check range hood inputs alert appears, fix the listed dimension, BTU, duct, rating, or trigger value before using the result tables and charts.

Interpreting Results:

Hood target is the rounded airflow target after the largest sizing driver and any buying reserve are applied. The Hood Sizing Table shows which driver set the base target, so a result driven by BTU deserves a range-manual check, while a result driven by kitchen volume deserves a closer look at room size and cooking intensity.

Candidate hood compares the entered model rating with the target. A Sized badge means the rating clears the target without extreme oversize, while Large headroom is not automatically better because extra airflow can add noise, duct cost, and makeup-air work.

Range hood result interpretation guide
Result cue	What to trust	What to verify
Rounded hood target	The planning CFM after reserve and 25 CFM rounding.	Manufacturer minimums, mounting height, and hood geometry.
Rating Ladder	Which common hood ratings are short, borderline, sized, or oversized.	Noise rating, certified airflow, and speed setting for the model.
Makeup air trigger	Whether the configured trigger is exceeded and how much planned replacement air is missing.	Local code language and combustion-appliance safety.
Duct diameter	Whether the entered round-equivalent duct keeps velocity within the planning range.	The hood manual's maximum equivalent length and allowed duct material.

Do not treat a green duct or candidate badge as installation approval. Use the Makeup Duct Checks details to find the weak point, then confirm the hood model, duct route, makeup-air plan, and permit requirements before buying or cutting ductwork.

Technical Details:

Residential range hood sizing combines capture guidance with practical planning rules. Width-based airflow estimates the plume capture need near the cooking surface. BTU-based airflow accounts for gas heat release. Room-volume airflow uses air changes per hour (ACH) to estimate how much exhaust may be needed to clear a larger cooking zone. The largest value sets the base CFM because the limiting condition matters more than the average of all conditions.

Duct checks are separate from capture sizing. CFM through a round duct becomes velocity in feet per minute (FPM), and velocity rises quickly as diameter shrinks because area changes with the square of the radius. A duct that is too small can make a suitable hood louder and less effective after installation.

Formula Core:

The airflow target is computed from width, gas output, kitchen volume, and a minimum floor, then rounded up to the next 25 CFM after any reserve is applied.

\begin{array}{lcl} Q_{width} & = & \frac{W_{hood}}{12} \times R_{location} \\ Q_{BTU} & = & \frac{total burner BTU/h}{100} \\ Q_{volume} & = & \frac{L \times D \times H \times ACH}{60} \\ Q_{base} & = & \max (Q_{width}, Q_{BTU}, Q_{volume}, Q_{minimum}) \\ Q_{target} & = & ceil to 25 CFM (Q_{base} \times (1 + \frac{r}{100})) \end{array}

Whood is hood width in inches, Rlocation is the CFM-per-foot rate for the hood location, L, D, and H are kitchen dimensions in feet, and r is the buying reserve percent. Metric entries are converted to the same inch and foot basis before the equations run. Electric and induction setups do not use the BTU driver, so that driver is treated as zero.

Range hood calculation constants
Quantity	Values used	Effect on result
Hood location rate	Wall or under-cabinet: `100 CFM/ft`; island or downdraft: `150 CFM/ft`.	Island and downdraft cases raise the width driver because capture is harder.
Cooking intensity ACH	Light: `10`; mixed: `15`; heavy: `20`; wok or griddle: `25`.	Higher ACH raises the kitchen-volume driver for smoke, heat, and odor clearing.
Reserve and rounding	Reserve is `0% to 35%` in the control; target rounds up to a `25 CFM` increment.	Small changes near an increment can move the displayed target to the next rating step.
Makeup-air trigger	Default `400 CFM`, editable for local requirements.	The makeup-air flag appears only when the target is greater than the trigger.

Duct velocity and makeup-air shortfall use the selected CFM target, hood rating, duct diameter, route length, fittings, and replacement-air capacity. These checks do not replace a manufacturer's duct table, but they identify common mismatches before a hood is ordered.

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

Range hood status boundary rules
Check	Boundary	Meaning
Candidate hood	`< -10%` headroom is Short; `-10% to < 0%` is Borderline; `0% to 35%` is Sized; above `35%` is Large headroom.	Headroom compares entered hood rating with the rounded hood target.
Duct diameter	A diameter below the common round size that keeps target CFM at or below about `1800 FPM` is marked Small duct.	The warning flags likely noise, pressure loss, or delivered-airflow loss.
Duct velocity	Chart points at or below `1800 FPM` are within the planning range; above `2200 FPM` is very high velocity.	The entered duct may be too small for the hood rating being considered.
Duct route	Equivalent length above `45 ft` asks for route verification.	Long runs and fittings should be checked against the hood manual.
Makeup air	`Qtarget > trigger` starts the makeup-air target; planned makeup air reduces any shortfall.	A target at exactly the trigger remains below the trigger flag.

For a 42 in wall hood over a 60,000 BTU/h professional-style gas range, the width driver is 350 CFM and the BTU driver is 600 CFM. A 14 ft x 14 ft x 9 ft kitchen at 20 ACH adds a volume driver of about 588 CFM. With no reserve, the base target is 600 CFM, and the rounded hood target remains 600 CFM.

Accuracy Notes:

These results are planning estimates for residential kitchen ventilation, not a permit decision or a guarantee of installed airflow.

Hood capture depends on mounting height, hood depth, side panels, burner position, pan size, cooking style, cross-drafts, and filter condition.
Nameplate CFM can differ from installed airflow after duct losses. Prefer certified ratings and manufacturer duct tables when available.
Makeup-air requirements vary by jurisdiction, appliance type, and combustion-air setup. Confirm the local rule before installing high-capacity exhaust.
Recirculating hoods can reduce some grease and odor at the hood, but they do not provide outdoor exhaust for moisture, heat, or combustion products.
Gas appliances, fireplaces, and large exhaust fans can interact through building pressure. Ask a qualified professional to review backdrafting and replacement-air risks when the exhaust capacity is high.

Advanced Tips:

Use Range and hood preset only as a starting point. Replace the preset BTU, hood width, kitchen dimensions, duct diameter, and elbow count with the actual appliance and route.
Treat Buying reserve as a deliberate product-selection margin. Too much reserve can push the result into louder fans, larger ducts, and makeup-air work.
Compare CFM Driver Chart before changing inputs. If one driver dominates, fix that physical issue first, such as hood width for capture or room volume for an open kitchen.
Use Duct Velocity Chart with the candidate hood rating, not only the target CFM. A model can meet the target while still driving the entered duct above the velocity warning range.
Change Makeup-air trigger when your local code, permit note, or appliance manual uses a value other than 400 CFM.
For downdraft, island, and professional gas setups, treat the result as an early estimate before reading the manufacturer ventilation table.

Worked Examples:

Professional gas range. A 36 in pro-style gas range with 60,000 BTU/h under a 42 in wall hood gives a Hood target of 600 CFM. With a 600 CFM candidate hood, Candidate hood is Sized; with the makeup-air trigger at 400 CFM and no planned replacement air, Makeup air trigger reports a 200 CFM planning shortfall.

At the makeup-air boundary. A 48 in wall hood over an electric cooktop produces a width driver of 400 CFM. If the trigger is also 400 CFM, Makeup air trigger stays Below trigger because the rule starts only when the rounded hood target is greater than the trigger.

Island hood with a large kitchen. A 42 in island hood over a 36 in gas cooktop in a 16 ft x 18 ft x 9 ft kitchen at heavy cooking intensity can be volume-driven, landing near an 875 CFM Rounded hood target. A 900 CFM hood may fit the airflow target, but the makeup-air target above a 400 CFM trigger is about 475 CFM.

Missing gas BTU. If Cooktop heat source is gas and Total burner output is left at 0, the red Check range hood inputs alert stops the tables. Enter the burner total from the range manual, or switch to Electric or induction when the appliance does not have gas BTU/h output.

FAQ:

How is gas range CFM estimated?

Gas and professional gas selections include a BTU driver equal to total burner BTU/h divided by 100. The final hood target uses the largest driver, so width or kitchen volume can still govern.

Does a 400 CFM hood always need makeup air?

No. The default trigger is 400 CFM, and the makeup-air flag starts when the rounded hood target is greater than that trigger. Change Makeup-air trigger if your local code uses a different value.

Why can the duct check fail when the hood rating looks right?

The Duct diameter check estimates velocity from CFM and round-duct area. A small duct can push velocity above the planning range even when Candidate hood is sized.

What should I fix when Check range hood inputs appears?

Read the alert list and correct the named value. The usual causes are zero dimensions, missing gas BTU, a zero duct diameter, a negative candidate rating, or a negative makeup-air trigger.

Can this estimate a recirculating hood?

The airflow comparison can still describe capture demand at the hood, but a recirculating selection is flagged because it does not provide true outdoor exhaust CFM.

Glossary:

CFM: Cubic feet per minute, the airflow rate used for the hood target and candidate hood rating.
ACH: Air changes per hour, used here to turn kitchen volume and cooking intensity into a CFM driver.
BTU/h: British thermal units per hour, the heat-output rating used for gas and professional gas burners.
Capture width: The hood width compared with the cooking surface, including extra overhang needs for exposed plume cases.
Makeup air: Replacement air supplied to offset air removed by high-capacity exhaust.
Equivalent duct length: A planning length that adds penalties for elbows and duct roughness to the straight duct run.
Recirculating hood: A hood that filters air and returns it to the kitchen instead of exhausting outdoors.

References:

How Much Ventilation Do I Need?, Home Ventilating Institute.
2024 International Residential Code, Chapter 15 Exhaust Systems, International Code Council.
Residential Ventilating Fans Version 4.1 Program Requirements, ENERGY STAR.