--- title: "Sizing a Range Hood: Width, Mounting Height and CFM for Wall and Island" description: "HVI's 100 and 150 CFM per foot, a canopy that covers the burners, the height windows makers print, and the duct a rating depends on." url: "https://rangehooderepair.center/guides/sizing-a-hood-and-its-airflow/" date_modified: "2026-09-26" --- Installation and setup # Sizing a Range Hood: Width, Mounting Height and CFM for Wall and Island Range hood CFM and size come down to three measurements. HVI recommends 100 CFM per linear foot of cooking surface for a wall hood and 150 for an island, so a 36-inch wall hood suits about 300 CFM. The canopy should cover the burners, and makers set the bottom edge roughly 18 to 30 inches above them. By [RangeHoodeRepair.center technical team](https://rangehooderepair.center/authors/technical-team/) Published September 26, 2026 ## At a glance. Width, mounting height and airflow are three separate numbers, and a hood that gets one of them wrong disappoints no matter how good the other two are. The published guidance on range hood CFM and size is short enough to fit on an index card. Read the whole guide ### Wall hood airflow 100 CFM per foot of width HVI's recommended rate; its stated minimum is 40 CFM per foot. ### Island hood airflow 150 CFM per foot of width HVI multiplies the wall rate by 1.5 for hoods over islands. ### Mounting height Set by the model, often 18 to 30 inches Broan's BCSD asks 18 to 24 inches; Vent-A-Hood says no more than 30. ### Professional-style burners Follow that maker's ventilation figure HVI defers to the cooking equipment manufacturer for pro-style surfaces. In this guide 1. Airflow: the HVI rule of thumb 2. Width: covering the burners you use 3. Mounting height: close enough to catch, far enough to work under 4. Matching airflow to the duct behind it 5. Step by step 6. Questions ## Airflow: the HVI rule of thumb The Home Ventilating Institute publishes the simplest starting point there is. For a hood against a wall it recommends 100 CFM for every linear foot of cooking surface, with 40 CFM per foot as the minimum. Over an island, where air moves in from every side and pushes the plume around, both figures rise by half. Airflow is measured in cubic feet per minute. HVI warns that inflated ratings are common on hoods that are not HVI-certified, so the figure worth comparing is the certified one, printed on the label or in the listing. *HVI airflow guidance for hoods against a wall (multiply by 1.5 over an island)* | Hood width | Recommended | Minimum | | --- | --- | --- | | 30 inches | 250 CFM | 100 CFM | | 36 inches | 300 CFM | 120 CFM | | 48 inches | 400 CFM | 160 CFM | ### Professional-style burners change the math High-output sealed burners, a griddle or an infrared element put far more heat and smoke into the air than a standard residential surface of the same width. HVI's guidance for those is to follow the manufacturer of the cooking equipment, whose installation manual usually states the ventilation it expects. ### Why more is not automatically better A bigger blower needs a bigger duct, makes more noise at the speeds people actually use, and pulls more conditioned air out of the house. Past a certain size, building codes also ask for make-up air, which is its own project. Pick the airflow the cooking needs, then size the duct to deliver it. Source: [Home Ventilating Institute — How Much Ventilation Do I Need?](https://www.hvi.org/resources/publications/home-ventilation-guide-articles/how-much-ventilation-do-i-need/) — 100 CFM recommended and 40 CFM minimum per linear foot against a wall, 150 and 50 over an island; 250/300/400 CFM for 30/36/48-inch wall hoods; follow the manufacturer for professional-style surfaces; inflated ratings are common on uncertified hoods; downdraft needs higher volume and cannot equal a canopy ## Width: covering the burners you use Smoke and steam widen as they rise. A canopy narrower than the cooking surface leaves the outer burners' plumes partly outside its reach, and those are often the burners used for searing. Matching the hood width to the cooking surface is the usual floor; going a size wider is the common upgrade for heavy cooks and for islands. Depth matters too. A shallow under-cabinet hood over a deep surface leaves the front burners outside the canopy, which is why so much smoke escapes at the front edge of an ordinary kitchen. Island hoods lose the wall that helps a wall hood. With no back surface to guide the plume upward, smoke drifts toward whichever side has the strongest draft, from an open door, a return grille or people walking past. That is part of why HVI raises the airflow over islands, and why many kitchens pair an island canopy with a width a size larger than the burners beneath it. - Measure the full width of the cooking surface, including side trim. - Measure its depth from the wall to the front of the front burners. - Compare both with the canopy dimensions in the hood's specification sheet. - Over an island, allow for air moving in from all four sides. Close on a tape measure stretched along the front edge of a range hood canopy. ## Mounting height: close enough to catch, far enough to work under Every manual prints a height window, and the windows differ. Broan's BXT1 under-cabinet series asks for the bottom of the hood to sit between 20 and 25 inches above the cooking surface for best capture; its BCSD series says no less than 18 and no more than 24. Vent-A-Hood recommends no more than 30 inches for both its wall and island hoods. Lower catches more, because the plume has less room to spread. Higher is easier on tall cooks and on the forehead, but the airflow needed for the same capture rises with every inch. ### Two manuals, one height The hood's range of heights and the cooking surface's minimum clearance above it both apply. Where they overlap, that overlap is the allowed window; where they do not, the pairing does not work and one of the two has to change. Source: [Broan — BXT1 Series Range Hood Installation Instructions](https://broan-nutone.com/getmedia/e05acdba-b6be-4e9e-8182-e44db1a97192/Installation-Guide-BXT1.pdf?ext=.pdf) — For best capture the bottom of the hood should be 20 to 25 inches above the cooking surface; [Broan — BCSD Series Range Hood Installation, Use and Care Manual](https://images.thdstatic.com/catalog/pdfImages/d0/d0c7024e-429d-40bf-b7bb-b697c67105be.pdf) — The bottom of the hood must be no less than 18 inches and no more than 24 inches above the cooking surface; [Vent-A-Hood — Wall Mount Range Hood Installation Instructions](https://www.ventahood.com/installpdfs/wall%20mount%20range%20hood%20installation%20instructions.pdf) — Bottom edge no more than 30 inches above the cooking surface; 300 CFM single blower on 6-inch round duct, 600 CFM dual blower on 8-inch round; never reduce the duct size; use only smooth galvanized metal duct, no flexible or corrugated, with as few turns as possible; [Vent-A-Hood — Island Range Hood Installation Instructions](https://www.ventahood.com/installpdfs/island%20range%20hood%20installation%20instructions.pdf) — Island hood bottom edge no more than 30 inches above the cooking surface ## Matching airflow to the duct behind it A rating is only reached through the duct it was tested with. Vent-A-Hood's wall instructions pair its 300 CFM single blower with 6-inch round duct and its 600 CFM dual blower with 8-inch round, and state that the duct size must never be reduced. A strong blower on a small or long duct delivers far less than its label. - The duct diameter the manual lists for that blower, carried the whole way out. - Smooth metal duct rather than flexible or corrugated. - As few elbows as the route allows. - A wall or roof cap sized to the duct, not a smaller one. Source: [Vent-A-Hood — Wall Mount Range Hood Installation Instructions](https://www.ventahood.com/installpdfs/wall%20mount%20range%20hood%20installation%20instructions.pdf) — Bottom edge no more than 30 inches above the cooking surface; 300 CFM single blower on 6-inch round duct, 600 CFM dual blower on 8-inch round; never reduce the duct size; use only smooth galvanized metal duct, no flexible or corrugated, with as few turns as possible ## Where to stop Sizing is a paper exercise an owner can do; installing is not. Wiring a hood into the house supply, cutting framing for a larger duct, or adding make-up air belongs with a qualified installer under local codes. If an existing hood seems undersized, have it checked before replacing it: a weak blower or a crushed duct can look exactly like a hood that was too small. Written by [RangeHoodeRepair.center technical team](https://rangehooderepair.center/authors/technical-team/). The crew that fixes kitchen range hoods here, writing from its own service visits and each maker's installation papers. Sources: [Home Ventilating Institute — How Much Ventilation Do I Need?](https://www.hvi.org/resources/publications/home-ventilation-guide-articles/how-much-ventilation-do-i-need/) · [Broan — BXT1 Series Range Hood Installation Instructions](https://broan-nutone.com/getmedia/e05acdba-b6be-4e9e-8182-e44db1a97192/Installation-Guide-BXT1.pdf?ext=.pdf) · [Broan — BCSD Series Range Hood Installation, Use and Care Manual](https://images.thdstatic.com/catalog/pdfImages/d0/d0c7024e-429d-40bf-b7bb-b697c67105be.pdf) · [Vent-A-Hood — Wall Mount Range Hood Installation Instructions](https://www.ventahood.com/installpdfs/wall%20mount%20range%20hood%20installation%20instructions.pdf) · [Vent-A-Hood — Island Range Hood Installation Instructions](https://www.ventahood.com/installpdfs/island%20range%20hood%20installation%20instructions.pdf) · [Broan — Automatic Make-Up Air Damper Application Guide](https://broan-nutone.com/getmedia/a31efbb7-8b9c-4931-ab22-2c905fe7c220/Broan-make-up-air-damper-application-guide.pdf) ## Step by step. Five steps, in the order worth doing them. 01 ### Measure the cooking surface Record its width and depth, and note whether it sits against a wall or in an island. 02 ### Work out the airflow Multiply the width in feet by 100 CFM for a wall hood or 150 CFM for an island, or use the pro-style maker's figure. 03 ### Check the height window Read the hood's and the cooking surface's installation manuals and confirm a height both allow. 04 ### Size the duct to match Use the duct diameter the hood's manual lists for that blower and do not reduce it anywhere. 05 ### Ask about make-up air If the chosen hood exceeds 400 CFM, check the local code before buying. For the heart of your home. ## Questions owners ask. ### How many CFM does a 30-inch wall hood need? HVI's recommended rate works out to 250 CFM for a 30-inch hood against a wall, with 100 CFM as its minimum. Heavy searing or high-output burners call for more, taken from the cooking equipment maker's manual. ### Should an island hood be larger than a wall hood? In airflow, yes: HVI multiplies the rate by 1.5 over an island. Many owners also choose a wider canopy there, because drafts from every side push the plume around more than a wall does. ### Can I mount the hood higher than the manual says? It will capture less, and the manual's window is the one the ratings assume. If you need more headroom, look for a model whose stated height range already covers it. ### Does a downdraft vent follow the same numbers? No. HVI notes that downdraft exhausters need higher volume and velocity to capture smoke and still cannot match a canopy above the surface; follow that unit's own specification. ## The problems behind it. Each has a page of its own: what it usually means and the causes in the order worth checking. [All 17 problems](https://rangehooderepair.center/problems/) Problem ### Range Hood Runs but Barely Pulls Smoke 7 causes, cheapest first Problem ### Range Hood Too Loud: Roar, Whine or Grinding 6 causes, cheapest first Problem ### Pop-Up Downdraft Vent Not Rising 6 causes, cheapest first ## When it needs a technician. The repairs on the right are where this guide ends when the checks do not settle it. ### Range hood diagnostic visit A visit that runs the hood through every speed and light, tests the draw at the filters and follows the air outside until one part is named. ### Range hood blower motor repair Testing and renewing the fan that moves a hood's air, in the canopy, the duct or on the roof: its capacitor, bearings, wheel or the motor itself. ### Range hood damper and duct repair Getting the air out of the house: the backdraft damper, the duct and its joints, the wall or roof cap, and make-up air in a tight house. ## More in installation and setup. Sizing a hood to the burners below, running the duct and fitting the backdraft damper, recirculating when no duct can reach outside, and the make-up air a strong blower needs in a tight house. [The whole section](https://rangehooderepair.center/guides/installation-and-setup/) Size, duct, damper and make-up air ### Range Hood Duct Runs and the Backdraft Damper: Size, Elbows and the Cap Outside Smooth metal at full diameter, five feet for every elbow, where a duct may and may not end, and how a flap that sticks lets in cold air or chokes the fan. Size, duct, damper and make-up air ### Make-Up Air for a Strong Range Hood: The 400 CFM Line and What It Protects Why a tight house fights a big blower, the code line above 400 CFM, backdrafting gas flues, where the intake goes and who sizes and tests it. Guides ### All 18 guides Six sections, by what you are trying to find out. --- **[Read on the site: Sizing a Range Hood: Width, Mounting Height and CFM for Wall and Island](https://rangehooderepair.center/guides/sizing-a-hood-and-its-airflow/)** **[Book a visit with RangeHoodeRepair.center](https://rangehooderepair.center/schedule/)**