Kitchen Exhaust Fan CFM Calculator

Estimate range hood airflow from hood width, cooktop BTU or watts, capture velocity, duct length, elbows, static pressure allowance, and the 400 CFM makeup-air trigger.

Hood width BTU or watts Capture velocity Duct static allowance

🏠Kitchen Hood Presets

Pick a real kitchen range-hood scenario, then adjust the eight sizing inputs. Presets include wall, island, under-cabinet, insert, and pro-style hood cases.

⚙Hood, Heat, Capture, And Duct Inputs

Hood mounting style Mounting style sets the width rule, default capture depth, and open-side penalty.

Cooktop cooking width (in) Use the actual burner or element spread, not the cabinet opening.

Hood capture width (in) Wider hoods improve capture; island hoods usually benefit from extra overhang.

Cooktop heat input basis Gas hoods often screen at about one CFM per 100 BTU/hr.

Total burner or element input (BTU/hr) Add burners that may run together; for electric, enter maximum watts.

Capture velocity target (fpm) Use lower values for mild wall hoods and higher values for island or heavy cooking.

Straight duct length (ft) Measure the actual run from hood outlet to exterior cap.

Duct fittings and static profile This profile supplies elbow equivalent length, duct diameter, and static allowance.

Check that widths, heat input, capture velocity, and duct length are valid positive numbers.

Kitchen exhaust fan CFM results

Recommended fan rating 0 CFM after duct allowance

Base capture requirement 0 higher of width, heat, velocity

Equivalent duct length 0 ft with elbow equivalents

Makeup air screen No 400 CFM trigger check

📊Hood And Fan Spec Summary

100 CFM per ft wall hood target

Common HVI recommended planning rate for wall-mounted kitchen range hoods.

150 CFM per ft island hood target

Open-side capture generally needs more airflow than a back-wall canopy.

400 CFM makeup air trigger

Many IRC-based jurisdictions screen range hood systems above this rating.

700-1200 fpm duct velocity band

Residential kitchen ducts are usually quieter when kept out of extreme velocity.

📘Kitchen Hood Reference Tables

Hood location	Minimum rate by width	Recommended rate by width	Calculator use
Against a wall	40 CFM per linear ft	100 CFM per linear ft	Width CFM = hood width in ft x 100, then adjusted for undersized capture width.
Island or peninsula	50 CFM per linear ft	150 CFM per linear ft	Open sides raise capture loss, so island presets use the stronger width rule.
Under-cabinet hood	40 CFM per linear ft	90 to 100 CFM per linear ft	Cabinet depth helps containment, but short hoods still need enough face capture.
Downdraft exhaust	Varies by product	Higher velocity path	The calculator adds a downdraft capture penalty and duct static allowance.

Cooktop heat input	Heat cross-check formula	Typical result	Sizing note
Gas range, 35,000 BTU/hr	BTU/hr / 100	350 CFM	Often close to a 30 in wall hood recommendation.
Gas cooktop, 65,000 BTU/hr	BTU/hr / 100	650 CFM	May exceed the 400 CFM makeup-air screen after duct allowance.
Electric, 8,000 watts	Watts x 3.412 / 100	273 CFM	Width and capture velocity commonly control more than heat input.
Induction, 11,000 watts	Watts x 3.412 / 100	375 CFM	Island exposure can still push the final recommendation higher.

Duct profile	Elbow equivalent	Static allowance	Best fit
Direct 6 in wall cap	0 ft fittings	0.04 in. w.c.	Short under-cabinet or wall hood below about 350 CFM.
Standard 7 in roof run	30 ft for two 90s	0.10 in. w.c.	Common wall hood path with roof cap and moderate turns.
Long 8 in route	45 ft for three 90s	0.16 in. w.c.	Island or remote exterior wall routes needing extra rating margin.
Tight 6 in route	60 ft for four 90s	0.24 in. w.c.	Restrictive retrofits where rated CFM may not equal delivered CFM.

Capture condition	Velocity screen	Area basis	Calculator effect
Light wall cooking	50 to 65 fpm	Hood width x shallow capture depth	Usually does not exceed the HVI width rate.
Normal wall cooking	65 to 85 fpm	Hood width x typical canopy depth	Useful cross-check for smoke and steam containment.
Island or open side	85 to 110 fpm	Wider, deeper exposed capture zone	Open-room air currents raise recommended airflow.
High heat searing	100 to 125 fpm	Large canopy face or downdraft slot	May require remote blower, larger duct, and makeup air review.

🔧Hood And Fan Spec Comparison Grid

Hood or fan type	Common rated CFM	Duct and static behavior	Best calculator match
Under-cabinet axial or compact blower	150 to 400 CFM	Short runs only; small wheels lose airflow quickly under static pressure.	Apartment, 24 to 30 in electric, or mild gas cooking below 400 CFM.
Wall canopy centrifugal blower	300 to 700 CFM	Handles normal 6 to 8 in ducts, one or two elbows, and roof caps.	Most 30 to 36 in wall gas ranges and mixed-fuel cooktops.
Island hood blower	500 to 1,000 CFM	Needs more width and airflow because the plume is exposed on all sides.	36 to 48 in island induction, gas, and high-output cooktops.
Remote inline or exterior blower	700 to 1,500 CFM	Better for long ducts, larger diameters, and noise-sensitive kitchens.	Pro-style ranges, long duct runs, and large custom canopy hoods.
Downdraft fan system	400 to 1,200 CFM	High turns and slot capture often need more static pressure allowance.	Island cooktops where overhead capture is not used.

💡Kitchen Exhaust Sizing Tips

Size for capture first, then check the duct.

A hood that is wide enough but connected to a tight 6 in duct with several elbows can miss its delivered airflow. The calculator raises the fan rating when equivalent length and static allowance increase.

Treat 400 CFM as a planning threshold.

The makeup-air result is a code screen, not a complete design. A tight home, fireplace, or atmospherically vented combustion appliance can make pressure balance important even near the threshold.

Range hoods must be able to move a specific amount of air from the kitchen to remove the smoke, steam, and grease from cooking. The amount of air that a range hood can move is measured in units of Cubic Feet per Minute, or CFM. The CFM of a range hood is the measurement of how many cubic feet of air that the range hood can pull through the hood every minute.

It is important to ensure that the range hood that is selected for the kitchen has the appropriate CFM because using a range hood with too little CFM will not effectively remove the smoke and grease from the kitchen, while using a range hood with too much CFM may lead to problems in the home due to the excess noise that it creates. When selecting a range hood, there is a few factor to consider. One of the main factor is the heat output of the cooktop that you will install in the range hood.

How to choose the right range hood CFM

Gas cooktops will create more heat and more smoke then induction cooktops, so more CFM is required from a range hood with a gas cooktop than with an induction cooktop. Additionally, the range hood should be wide enough to cover the cooking area of the cooktop. As the hot air rise from the cooktop, it will spread outward from the cooktop.

If the range hood is too narrow for the cooktop, the hot air will go past the range hood and enter the kitchen instead. Another factor that can impact the CFM of the range hood are the ductwork and the resistance of that ductwork. Any elbow in the ductwork will create resistance for the range hoods fan to move the air through the ductwork.

Additionally, any length of the ductwork will create resistance for the fan of the range hood. For instance, if the range hood is connected to a long duct full of elbows, the range hood will have to work harder to move the air than if it was connected to a short straight duct. Thus, two kitchen may require different CFM ratings for the same range hood if the ductwork in each range hood creates different amount of resistance for the fan to move the air.

Another consideration for CFM is the makeup air that must be provided for the home. Building code require makeup air in homes with high-capacity appliances like range hoods because if the range hood continuously pulls the air out of the home, the home may become negatively pressurized. If the home is negatively pressurized, the range hood may pull air down the chimney or impact other appliance in the home.

Thus, it is important to make sure that the home has a way to provide makeup air for the kitchen when the range hood is operating at high CFM rating. Range hoods are also rated according to the velocity at which the hood pull the air from the cooking area towards the hood. This velocity is measured in feet per minute.

The mounting style of the range hood can impact the requirement for the velocity of the range hood. For instance, if the range hood is mounted on the wall, there will be a wall behind the hood that will help to contain the air that the range hood pulls. Range hoods that is installed on kitchen islands, however, are located in an open area.

Thus, the rising hot air will drift away from the range hood more easy than if it were behind a wall. Therefore, island range hoods will have to move more air to maintain an appropriate capture velocity so that smoke and grease will be removed from the island. Finally, people can make a few mistake when selecting a range hood.

For instance, many people will purchase a range hood with a very high CFM rating because they think that high CFM ratings are always better. In reality, range hoods with high CFM ratings will not work well if the ductwork of the range hood is too small. Additionally, some people will undersize the range hood in that they will only consider the width of the cooktop that will be installed in the range hood but fail to consider the impact of the ductwork.

Thus, the CFM ratings of the range hood have to be set to the proper airflow rating for the range hood, the cooktop, and the ductwork that the installation of the range hood will be create by to ensure the kitchen is free of smoke and grease and that the range hood does not cause grease to settle on the kitchen cabinet. Actually, you should of checked the vent size first. Most people dont realize how much it matters for the furnitures in the room too.