Range hood CFM calculator: start with the cooking surface, not a long questionnaire
Most people looking for a range hood do not have a duct static-pressure calculation, a complete kitchen drawing and every appliance specification ready. This calculator therefore starts with the information that is normally easiest to know: cooktop type, cooktop width, hood location and whether the hood exhausts outdoors.
Those basic inputs produce a practical airflow target in CFM or m³/h. Gas BTU, kitchen volume, a candidate hood and duct details are optional checks rather than obstacles placed in front of the answer.
- Range hood airflow target in CFM or m³/h
- Wall-mounted versus island hood sizing
- Optional gas-burner BTU cross-check
- Optional 15-ACH kitchen-volume cross-check
- Candidate-hood comparison
- Ductwork, recirculation and make-up-air warnings
- England Part F 2026 local-extract check when selected
For a quick shopping answer, use the four main fields and stop there. Open Advanced settings only when you know the gas BTU, want to test a hood model, have an unusually large kitchen or need to review the exhaust path.
The quick rule: CFM per linear foot of cooktop
The Home Ventilating Institute publishes a useful residential planning rate based on cooking-surface width and hood position. A hood against a wall has an easier capture job than a canopy hanging over an island, where cross-currents can approach from every side.
HVI range hood planning rates
| Hood location | Recommended rate | Quick example |
|---|---|---|
| Against a wall | 100 CFM per linear foot | 30 in cooktop = 2.5 ft → 250 CFM |
| Over an island | 150 CFM per linear foot | 36 in cooktop = 3 ft → 450 CFM |
The calculator uses that width-based result as the first sizing check. It does not automatically inflate the number for every possible complication; instead, optional checks are shown separately so you can see why a higher target appears.
Gas range hood CFM: add total burner BTU when you know it
A high-output gas range can need more ventilation than width alone suggests. Broan-NuTone publishes the common planning guideline of approximately 1 CFM per 100 BTU/h for high-output gas cooking. The calculator compares that BTU result with the width result and keeps the larger value.
What happens with a 36 in wall-mounted gas range rated at 60,000 BTU/h?
Answer: The width method gives 3 ft × 100 = 300 CFM. The gas-output check gives 60,000 ÷ 100 = 600 CFM. The practical selection target is therefore driven by the 600 CFM gas result.
Explanation: Two ranges can be the same width but have very different total burner output. The BTU check prevents a high-output gas appliance from being treated like a modest cooktop simply because both fit in the same cabinet opening.
BTU is optional. If the range specification is not available, leave the field at zero rather than guessing. The width-based result remains usable as a first estimate.
Why an island hood needs more airflow
A wall helps contain the plume from the cooktop. An island canopy has no back wall, so smoke, steam and grease can drift away in more directions before the hood captures them. That difference is why the HVI planning rate increases from 100 to 150 CFM per linear foot for an island installation.
How much airflow does a 30 in island cooktop produce in the quick calculation?
Answer: Thirty inches is 2.5 ft. At 150 CFM per linear foot, the result is 375 CFM. A shopper would normally compare models around 400 CFM or higher, subject to the appliance and installation instructions.
Explanation: The rounded shopping class makes model comparison easier while the calculator still preserves the exact 375 CFM check in the detailed result.
Optional kitchen-volume check for large or tall rooms
If you enter kitchen length, width and ceiling height in Advanced settings, the calculator adds a 15-air-changes-per-hour cross-check, equivalent to replacing the room volume about once every four minutes. Zephyr publishes this as a second way to assess kitchen airflow and recommends comparing it with cooking-surface sizing.
Do not blindly use the entire volume of a huge open-plan floor. A range hood is primarily a source-capture device above the cooking surface. Treat the room-volume method as a cross-check, not a reason to turn every open kitchen into a commercial exhaust system.
Duct length and elbows: why this calculator does not fake a CFM penalty
Ducted vs ductless range hoods
A ducted hood sends captured air outdoors. A recirculating or ductless hood passes air through filters and returns it to the kitchen. The blower may still have a CFM rating, but that does not mean the two systems remove moisture, heat and combustion pollutants in the same way.
When recirculating mode is selected, the calculator still provides a blower-size planning target but clearly separates it from outdoor-extract ventilation requirements.
The 400 CFM make-up-air question
Powerful kitchen exhaust can depressurize a tight house. In the 2024 IRC, Section M1503.6 addresses exhaust systems capable of more than 400 CFM where qualifying gas, liquid or solid-fuel appliances that are neither direct-vent nor mechanically drafted are located inside the dwelling air barrier. Local code adoption and amendments matter, so the calculator flags the issue rather than claiming every 401-CFM hood has the same legal requirement everywhere.
Make-up air is not simply another number to add to the hood CFM. It is a building-system issue involving pressure balance, combustion safety, outdoor-air path, dampers and local requirements.
England Part F 2026: the kitchen extract minimum is a different question
Approved Document F 2026 for dwellings in England gives 30 L/s for intermittent kitchen extract where a cooker hood extracts to the outside. Where there is no cooker hood, or the cooker hood does not extract outdoors, Table 1.1 gives 60 L/s for kitchen extract. The 2026 edition takes effect in England on 24 March 2027, or 24 September 2027 for higher-risk buildings. Check the transitional provisions and the edition applicable to your project before using this mode for a compliance assessment.
Those figures are minimum local ventilation rates, not a replacement for capture sizing above a particular range. A 30 in or 36 in cooktop may reasonably lead to a much larger practical hood airflow than the Part F minimum. The calculator therefore shows the Part F figure as its own check instead of pretending the two methods answer exactly the same question.
Three worked range hood examples
Quick sizing examples
| Kitchen setup | Checks | Planning target |
|---|---|---|
| 30 in electric/induction, wall hood | 2.5 ft × 100 CFM/ft | 250 CFM → compare roughly 300-CFM models |
| 36 in electric/induction, island hood | 3 ft × 150 CFM/ft | 450 CFM → compare roughly 450–500 CFM or higher |
| 36 in gas, wall hood, 60,000 BTU/h | 300 CFM by width; 600 CFM by gas output | 600 CFM because the BTU check is higher |
Common range hood sizing mistakes
What goes wrong and what to do instead
| Mistake | Why it fails | Better check |
|---|---|---|
| Sizing only from kitchen floor area | It ignores source capture over the cooktop | Start with cooktop width and hood location |
| Ignoring gas burner output | A high-BTU range can be undersized by width alone | Add total BTU when available |
| Adding a fixed CFM number per elbow | Duct resistance is system-specific | Use manufacturer duct limits and performance data |
| Treating recirculation as outdoor exhaust | Filtered air remains indoors | Separate blower sizing from ventilation compliance |
| Buying the highest CFM available | Noise, duct size and make-up air can become harder problems | Choose enough airflow with good capture and a proper duct path |
What to check on the actual hood specification
- Rated airflow and whether it is an HVI-certified or manufacturer maximum figure
- Hood width and depth relative to the cooktop
- Allowed mounting-height range
- Required duct diameter or rectangular duct size
- Maximum equivalent duct length and fitting limits
- Noise at the speeds you will actually use
- Recirculation kit and filter requirements if outdoor exhaust is impossible
- Make-up-air and local-code requirements before choosing a very high-CFM model
Range Hood CFM Calculator FAQ
How many CFM do I need for a 30 inch range?
A 30 in cooktop is 2.5 ft wide. The HVI planning rate gives 250 CFM for a wall installation and 375 CFM for an island installation. A high-output gas range may require a larger result when total burner BTU is checked.
Is 400 CFM enough for a gas range?
Sometimes, but not always. A 40,000 BTU/h gas appliance gives about 400 CFM under the 1-CFM-per-100-BTU planning rule. A 60,000 BTU/h appliance gives 600 CFM. Width, hood location and the appliance manufacturer's instructions still need to be checked.
Should I add extra CFM for a long duct?
Do not rely on one universal percentage or fixed number. A long duct can reduce delivered airflow, but the effect depends on duct size, fittings and the blower curve. Choose the permitted duct layout first and verify the selected hood's performance data.
Does a ductless range hood need the same CFM?
The blower still moves air, but a ductless hood returns filtered air to the kitchen. Its CFM therefore should not be interpreted as the same outdoor-pollutant removal provided by a ducted hood. Follow the recirculating kit and appliance instructions for the selected model.
Why does the calculator not ask for kitchen dimensions immediately?
Because cooktop capture is the primary question for a range hood and most users know the range width before they know the exact kitchen volume. Room dimensions remain available as an optional cross-check for large or tall kitchens without making every user fill in unnecessary fields.
Use the result as a model-selection target, not a duct design
Start with the recommended airflow, then compare real hoods that fit the cooktop width and mounting position. Before purchase, check the installation height, duct size, equivalent-length limit, sound level and any make-up-air requirement. A correctly sized hood with poor capture geometry or restrictive ductwork can perform worse than a slightly smaller hood installed as designed.
How HomDera documents calculator formulas, assumptions and limitations