Range Hood CFM Sizing: The Right Airflow for Every Kitchen Setup

Undersized range hoods leave grease and smoke in the kitchen. Oversized ones waste energy and money. Here is the correct CFM calculation for gas cooktops, electric cooktops, and professional ranges.

Why Range Hood Sizing Matters

A range hood that is too small leaves smoke, grease particulate, and combustion byproducts in the kitchen air. One that is too large circulates conditioned air out of the house at a rate that wastes energy and creates backdrafting in other appliances. Getting the CFM (cubic feet per minute) right is one of the most consequential decisions in a kitchen spec — and it is frequently done wrong.

This article covers the correct calculation method, how to apply it to gas versus electric cooktops, what ductwork configuration changes, and the make-up air requirements that code increasingly enforces.

The Base CFM Formula

The starting point for any range hood calculation is the cooking surface width.

Standard recommendation: 100 CFM per linear foot of cooktop width.

This is the figure used by most major manufacturers (Broan, Zephyr, Thermador, Wolf) and supported by HVI (Home Ventilation Institute) guidelines. For a 30-inch electric smooth-top range, that is 100 CFM minimum. For a 48-inch professional gas range, that is 400 CFM minimum.

CFM by Cooktop Width (Baseline)

| Cooktop Width | Minimum CFM | |---|---| | 30 inches | 100 CFM | | 36 inches | 150 CFM | | 42 inches | 175 CFM | | 48 inches | 200 CFM | | 60 inches | 250 CFM |

These are the baseline numbers. Actual requirements escalate from here based on fuel type and cooking intensity.

Gas Cooktops: Higher CFM Requirements

Gas cooktops produce more heat, combustion byproducts (nitrogen dioxide, carbon monoxide), and moisture than electric units. The extra heat load means a gas range needs roughly 150-200 CFM per linear foot rather than 100 CFM.

CFM for Gas Cooktops

| Cooktop Width | Recommended CFM (Gas) | |---|---| | 30 inches | 300-400 CFM | | 36 inches | 400-500 CFM | | 42 inches | 500-600 CFM | | 48 inches | 600-800 CFM | | 60 inches | 800-1,000 CFM |

A 36-inch gas cooktop producing 65,000 BTU input (common for a mid-range gas cooktop) requires a minimum of approximately 400 CFM at the hood. A professional-style 48-inch range with 100,000+ BTU may need 800-1,000 CFM.

BTU-to-CFM conversion note: As a rough guide, 100 CFM is needed for every 10,000 BTU of gas cooktop input. This is a conservative baseline — actual requirements vary based on burner configuration, hood height, and duct run length.

Professional and High-Output Ranges

Restaurant-style ranges and open-burner setups produce significantly more grease-laden smoke and combustion byproducts than sealed-burner residential units. For commercial-style ranges (e.g., 6+ burners, open grates, chef-grade output):

• Minimum 600 CFM for 36-inch units
• 800-1,200 CFM for 48-inch and wider units

Electric Cooktops: Lower but Not Zero Requirements

Electric cooktops produce no combustion byproducts but still generate grease particulate, steam, and heat that must be vented. The baseline 100 CFM per linear foot applies.

For an electric smooth-top or induction cooktop:

• 30-inch cooktop: 100-150 CFM
• 36-inch cooktop: 150-200 CFM
• Induction or radiant glass cooktops: same as above, with consideration for higher smoke points from searing and wok cooking

Hood Height: How It Changes CFM Requirements

The distance between the cooktop surface and the bottom of the range hood affects capture efficiency. The higher the hood, the more CFM required to capture and remove the same amount of smoke.

Rule of thumb: Add 100 CFM for every 3 inches of additional hood height above the standard 24-inch mounting height.

| Mounting Height | CFM Multiplier | |---|---| | 18 inches | 0.85x (closer = more efficient) | | 24 inches | 1.0x (baseline) | | 30 inches | 1.15x | | 36 inches | 1.3x | | 42 inches | 1.45x |

This matters in kitchen designs with raised ceilings or islands where the hood is mounted significantly above the 24-inch minimum. A 36-inch gas cooktop with the hood mounted at 36 inches instead of 24 inches requires approximately 30% more CFM to maintain equivalent capture performance.

Ductwork Configuration and Its Effect on Performance

CFM at the hood does not equal CFM at the exhaust outlet. The duct run is a significant variable that determines how much of the rated airflow actually reaches the outside.

Duct Diameter and CFM Capacity

| Duct Diameter | Maximum Recommended CFM | |---|---| | 6-inch round | Up to 300 CFM | | 7-inch round | Up to 500 CFM | | 8-inch round | Up to 750 CFM | | 3-1/4 x 10 rectangular | Up to 400 CFM | | 7 x 10 rectangular | Up to 550 CFM | | 8 x 12 rectangular | Up to 700 CFM |

Using an undersized duct run with a high-CFM hood is one of the most common installation errors. A 600 CFM hood on a 6-inch duct will perform like a 300 CFM hood — the duct is the bottleneck.

Maximum Duct Length

The longer the duct run, the more static pressure loss occurs before air exits the house. Most manufacturers specify maximum straight-run lengths before a significant performance drop:

• 8-inch round duct: up to 50 feet of straight run before significant performance loss (with no elbows)
• 6-inch round duct: up to 30 feet of straight run

Minimum velocity: To maintain airflow and prevent grease settling in the duct, maintain a minimum of 500 linear feet per minute (LFM) velocity in the duct. This is achieved with the CFM and duct diameter combinations above.

Make-Up Air Requirements

When a range hood exhausts more than 300-400 CFM continuously, it begins to create negative pressure in the home. This can:

• Backdraft gas furnaces, water heaters, and fireplaces (creating a carbon monoxide hazard)
• Cause doors to slam or stick
• Draw unconditioned outside air through gaps in the building envelope, negating energy efficiency gains elsewhere

Make-up air options:

• Passive make-up air register (in the kitchen wall or floor near the hood): Simple, inexpensive, but can be drafty in cold climates.
• Motorized make-up air damper: Linked to the range hood switch; opens only when the hood runs. More energy-efficient.
• Heat-recovery ventilator (HRV) or energy-recovery ventilator (ERV) integration: For high-performance homes targeting specific ACH targets; the make-up air is conditioned before entry.

Noise: CFM vs. Sones

CFM and noise are directly related. Higher airflow means more noise — but the relationship is not linear.

Sones are the unit of perceived loudness. One sone is roughly the sound of a quiet refrigerator. A typical residential kitchen conversation is 40-50 decibels, which falls in the 4-5 sone range.

| Sones | Approximate dBA | Perception | |---|---|---| | 0.5 | 35 | Very quiet; barely audible | | 1.0 | 40 | Quiet; like a library | | 2.0 | 45 | Moderate; noticeable | | 3.0 | 52 | Loud; conversation requires raised voice | | 5.0 | 60 | Very loud; normal conversation difficult |

Most premium range hoods move the noise-per-CFM needle significantly:

• Budget/builder-grade hoods at 400 CFM: 5-8 sones
• Mid-range hoods at 400 CFM: 2-4 sones
• Premium hoods (Zephyr Monsoon, Broan Elite, Wolf): 1-3 sones at 400 CFM

CFM at Altitude

At elevations above 4,000 feet, gas burners produce less heat per BTU and more incomplete combustion. Range hood CFM requirements do not change significantly with altitude, but gas cooktop BTU ratings should be de-rated by approximately 4% per 1,000 feet above sea level. A 65,000 BTU cooktop at 7,000 feet effectively delivers approximately 56,000 BTU. Adjust your CFM recommendation accordingly.

Also note that at altitude, make-up air considerations are more critical — the home is already at lower air density, and exhaust appliances are more prone to backdrafting.

Quick Reference: Final CFM Numbers

| Configuration | Typical CFM Range | |---|---| | 30" electric smooth-top | 100-200 CFM | | 36" electric smooth-top | 150-300 CFM | | 30" gas cooktop (standard) | 300-400 CFM | | 36" gas cooktop (standard) | 400-600 CFM | | 36" pro-style gas range | 600-1,000 CFM | | 48" pro-style gas range | 800-1,200 CFM |

These are ranges, not absolutes. The final number depends on cooking habits, kitchen layout, duct run, and hood mounting height.

Specifying and Sourcing

Getting the CFM right in the spec is only half the battle. The hood itself needs to match the application:

• Under-cabinet hoods: Good for 300-600 CFM residential setups. Most common installation type.
• Wall-mount chimney hoods: Can handle 400-1,200 CFM. Common for pro-style ranges.
• Island hoods: Require stronger CFM because they capture from all sides; add 20% CFM over equivalent wall-mount specs.
• Downdraft hoods: Inadequate for gas cooktops above 40,000 BTU. Downdraft systems are only appropriate for electric cooktops.

---

The right CFM is a function of cooktop width, fuel type, hood height, and duct configuration. Run the calculation before you spec the hood, not after.

---

Sourcing range hoods at contractor pricing? Connect with Buildtana for direct-from-manufacturer options across the full CFM range.