What Size Range Hood Do I Need? CFM for Gas and Electric
Part of the project planner: Planning heating, cooling and ventilation.
A gas cooktop with 60,000 BTU of burners needs a range hood of about 600 CFM against a wall, or 750 CFM over an island, with an 8 inch duct. An electric 30 inch cooktop needs about 300 CFM. The charts below give the figures for other cooktops.
Gas cooktops: CFM by burner output
One CFM for every 100 BTU, checked against a 14 × 12 × 8 ft kitchen (336 CFM for 15 air changes an hour):
| Total burner output | Wall hood | Island hood | Duct size |
|---|---|---|---|
| 30,000 BTU | 350 CFM | 450 CFM | 6 in |
| 40,000 BTU | 400 CFM | 500 CFM | 6 in |
| 50,000 BTU | 500 CFM | 650 CFM | 8 in |
| 60,000 BTU | 600 CFM | 750 CFM | 8 in |
| 80,000 BTU | 800 CFM | 1,000 CFM | 10 in |
| 100,000 BTU | 1,000 CFM | 1,250 CFM | 10 in |
Electric and induction cooktops: CFM by width
| Cooktop width | By the cooktop (100 CFM per 10 in) | CFM to shop for | Duct size |
|---|---|---|---|
| 24 in | 240 CFM | 350 CFM | 6 in |
| 30 in | 300 CFM | 350 CFM | 6 in |
| 36 in | 360 CFM | 400 CFM | 6 in |
| 48 in | 480 CFM | 500 CFM | 8 in |
The last two columns include the check against the size of the kitchen. Use the range hood CFM calculator for your own cooktop and kitchen.
Two ways to size it
- By the cooktop. The heat and the grease depend on how much you cook: 1 CFM per 100 BTU for gas, or 100 CFM per 10 inches of width for electric.
- By the kitchen. A hood should change the air about 15 times an hour in a typical kitchen: the room volume times 15, divided by 60.
- Use the higher of the two, and add about 25% over an island or peninsula, where the fumes can drift sideways.
The details that matter as much as CFM
- Duct size and length. A 6 inch duct suits up to about 400 CFM, 8 inch up to about 700, and 10 inch up to about 1,000. Every elbow and extra foot of duct cuts the real airflow, so a powerful hood on a poor duct can perform like a weak one.
- Width and height. The hood should be as wide as the cooktop or wider, and 24 to 30 inches above it.
- Make-up air. Many codes require a make-up air system for hoods over 400 CFM, so that the fan does not pull combustion gases back down a flue. This can add cost, so ask your building department before you choose a 1,000 CFM hood.
- Noise. Check the sone rating at the speed you will use. Many people turn a loud hood off.
- Ducted or recirculating. Venting outside is always better. A recirculating hood only filters grease.
Mistakes that cost people money
- Buying the biggest hood without checking whether the code needs make-up air.
- A hood narrower than the cooktop, which misses the outer burners.
- Using flexible duct and several elbows, which cut the airflow.
- Choosing by price, not by the CFM at the duct length you actually have.
Frequently asked questions
How many CFM do I need for a gas range?
About 1 CFM for every 100 BTU of burner output. A typical 60,000 BTU range needs about 600 CFM, and a 36 inch pro-style range of 100,000 BTU needs 1,000 CFM.
What size range hood do I need for a 30 inch electric range?
About 300 CFM by the cooktop rule (100 CFM per 10 inches of width), though most people choose 300 to 400 CFM. The hood should be at least as wide as the cooktop.
Do I need make-up air for a range hood?
Many codes require it above about 400 CFM, because a strong hood can pull exhaust gases back down other flues. Check with your building department.
Do range hoods over an island need more CFM?
Yes, about 25 to 50% more, because there is no wall behind the cooktop to help capture the rising fumes, and cross-drafts pull it away.
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.