Range Hood CFM Calculator
Range hood CFM from burners and width with makeup air guidance.
What it does
Range hoods size two ways and take the larger: gas burners demand 100 CFM per 10,000 BTU while the hood width demands 100 per foot (150 island). Past 400 CFM, makeup air joins the plan.
The tool above takes BTU with width and mount. It returns CFM with makeup air and the governing rule.
The default 50,000 BTU under 2.5 ft wall needs 500 CFM with 100 makeup, gas governing. An all-electric 3 ft wall needs 300 with none.
Sizing follows HVI ventilation guides with Energy Star and code pages behind them. All three agree on 100/100-150 and the 400 makeup line used here.
How to use
- Enter total burner BTU.
- Enter hood width in feet.
- Pick wall or island mount.
- Read CFM first.
- Read makeup air beside it.
- Vent outdoors, upsize ducts.
Formula
- BTU
- Total burner BTU per hour.
- width
- Hood width in linear feet.
- 400
- 400 CFM standard threshold.
Minimums run 40 CFM/ft wall and 50 island with HVI certifying rounded down. Some codes lift makeup to 600 CFM for all-direct-vent houses. Size up, never down.
Worked example
Example: 50k BTU gas range
Defaults: 50,000 BTU, 2.5 ft wall hood.
- Cooktop: 50,000 BTU gas.
- Gas: 50,000 / 100 = 500 CFM.
- Structure: 2.5 ft wall x 100 = 250 CFM.
- Pick: max(500, 250) = 500 CFM.
- Makeup: 500 - 400 = 100 CFM.
- Gas governs over structure.
- Tool shows 500 CFM, 100 CFM makeup air.
Reference table
| Width | Wall | Island |
|---|---|---|
| 30 in (2.5 ft) | 250 | 375 |
| 36 in (3 ft) | 300 | 450 |
| 48 in (4 ft) | 400 | 600 |
Limits
- US sizing practice; codes vary.
- Duct losses need upsizing.
- Downdrafts need more.
- Pro ranges follow makers.
Common mistakes
- Sizing by width alone.
- Skipping makeup past 400.
- Recirculating for ventilation.
- Ignoring duct losses.
- Under-sizing islands.
Try it yourself
Quick checks. Answers sit tucked under each question.
All-electric 3 ft wall?
Gas 0, structure 300: 300 CFM, no makeup.
30k BTU, 3 ft island?
Gas 300 vs 450 structure: 450 CFM, 50 makeup.
120k BTU pro range, 3 ft wall?
Gas 1,200 vs 300: 1,200 CFM, 800 makeup.
Questions
How is hood CFM sized?
100 CFM per 10,000 BTU for gas; 100 per foot wall (150 island) for structure. Take the larger.
When is makeup air needed?
At or past 400 CFM: makeup about equal to the excess, interlocked with the hood.
Do ductless hoods ventilate?
No: recirculating hoods give no ventilation. Vent outdoors for real exhaust.
Do ducts change sizing?
Yes: long runs and elbows cut delivered CFM, so size the blower up.
What about islands and pro ranges?
Island rate runs 1.5x wall; pro ranges follow maker specs when higher.
Do downdrafts match canopies?
No: downdrafts capture worse and always need higher rates.