Most homeowners shop for a range hood by asking “how many CFM?” — but that is almost the wrong question. Proper hood capture efficiency can vary 10× depending on design and airflow, meaning placement and ducting matter more than fan “max CFM”. Source. A poorly mounted 1,200 CFM hood can perform worse than a well-placed 400 CFM unit. This guide cuts through the specs and tells you exactly what drives real kitchen air quality — and what gear actually delivers it.

Kitchen Range Hood Efficiency: Why CFM Is Only Half the Story

What Cooking Actually Puts Into Your Air

Every time you cook — especially on gas — you release a cocktail of pollutants that most people never consider. Understanding what you are actually dealing with sets the right context for every decision that follows.

• PM2.5 (fine particles): Frying at high heat can generate PM2.5 spikes that can reach 200–500 µg/m³ within minutes, 25-60 times the EPA’s annual standard of 9 µg/m³. Particles this small, ≤2.5 micrometers, bypass nasal defenses and deposit directly in lung tissue.
• NO2 (nitrogen dioxide): Gas burners routinely push kitchen NO2 above 200–400 ppb during cooking. The WHO’s 24-hour guideline is 25 ppb. Even brief repeated exposures at cooking levels are associated with reduced lung function, particularly in children.
• CO (carbon monoxide): Incomplete combustion — common when burner grates are dirty, or flames are starved of oxygen — produces CO. A poorly ventilated kitchen running a high-BTU gas range can accumulate CO faster than many homeowners expect.
• VOCs (volatile organic compounds): Heated cooking oils and nonstick coatings off-gas VOCs,s including acrolein and formaldehyde. These contribute to odor and are respiratory irritants at elevated concentrations.
• Moisture and grease aerosols: Uncaptured steam sharply raises kitchen RH. Grease aerosols coat duct interiors, reducing airflow over time and creating a fire hazard.

The core point: cooking is one of the single largest episodic sources of indoor air pollution in a home. A range hood that performs well during actual cooking events — not just on a spec sheet — is a genuine health tool.

Cooking Air Quality — Quick Facts

Pollutant	Source	Indoor Peak (Cooking)	Health Benchmark
PM2.5	Frying, searing	200–500 µg/m³	<9 µg/m³ (EPA annual)
NO2	Gas burners	200–400 ppb	25 ppb (WHO 24-hr)
CO	Gas combustion	5–50 ppm (varies)	<9 ppm (EPA 8-hr)
VOCs	Oils, coatings	Variable; often 2–5× baseline	No single standard; minimize
Moisture (RH)	Boiling, steam	Can spike 15–30% RH above baseline	40–50% RH (EPA target)

Summary: Cooking on gas generates NO2, PM2.5, CO, and VOCs at concentrations that routinely exceed health guidelines within minutes. A high-performing range hood — one that truly captures the convective plume rather than simply moving air — is the primary defense against kitchen-generated indoor air pollution.

The Science of Capture Efficiency: Why Your Hood May Be Failing You

Capture efficiency is the percentage of cooking pollutants that a hood actually intercepts before they disperse into the kitchen. It is the most important metric that most product listings never mention.

The Physics of the Cooking Plume

When a burner heats food, the rising column of hot air and combustion gases forms a buoyant convective plume. This plume is roughly cone-shaped, widening as it rises. By the time it reaches hood height — typically 24–30 inches (61–76 cm) above the cooktop — the plume diameter has expanded significantly. If the hood face is smaller than the plume cross-section at that height, a portion of the plume spills sideways into the room before it can be captured. That spillage is irreversible: once pollutants enter the kitchen air, no amount of fan speed retrieves them efficiently.

This is why two hoods with identical CFM ratings can differ dramatically in real performance. A deep-bodied hood with a large capture area and low mounting height catches more of the plume at a stage when it is still narrow and fast-moving. A shallow decorative hood mounted high intercepts the plume only after it has widened and slowed — and misses a large fraction of it regardless of fan speed.

ASTM E3087: The Standard Most Shoppers Have Never Heard Of

ASTM E3087 is the test protocol for measuring residential range hood capture efficiency under realistic cooking conditions. Rather than measuring raw airflow in a lab, it uses tracer gases and cooking simulations to determine what fraction of actual cooking emissions are captured. Hoods tested under E3087 often show efficiency ratings between 30% and 95% at various fan settings — a range that makes raw CFM comparisons almost meaningless without context. Look for manufacturers that reference E3087 data; those that do not are not necessarily failing, but the absence of the data leaves you guessing.

What the 10× Efficiency Difference Looks Like in Practice

Research consistently shows that hood capture efficiency varies by roughly 10-fold between poor and optimal installations of the same equipment in the same CFM class. The variables that drive this gap:

• Mounting height: Every inch above the recommended 24–30 inches (61–76 cm) reduces capture. At 36 inches (91 cm), plume spillage increases substantially on standard burner configurations.
• Hood width relative to cooktop: A hood that matches or extends 3 inches (7.6 cm) beyond each burner edge captures the plume perimeter. A hood narrower than the cooktop prevents the outer burner plumes from escaping entirely.
• Duct diameter and run length: Undersized or kinked flex duct creates static pressure that chokes actual airflow to a fraction of rated CFM. A 6-inch (15 cm) duct on a 600 CFM hood is undersized; an 8-inch (20 cm) round or equivalent rectangular duct is the practical minimum for high-output hoods.
• Number of elbows: Each 90° elbow in a duct run typically reduces effective airflow by the equivalent of 10–15 feet (3–4.6 m) of straight duct. Two tight elbows on a short duct run can cut delivered airflow by 25–35%.
• Crossflows and makeup air: Open windows, HVAC supply vents, or exhaust fans elsewhere in the house create crossflow currents that deflect the cooking plume to the sides, reducing capture even from a correctly sized and positioned hood.

Summary: Capture efficiency — not maximum CFM — determines how much cooking pollution actually leaves your kitchen. Mounting height, hood width, and duct design are the three variables with the largest impact. A well-designed 400 CFM installation can outperform a 1,200 CFM unit that is poorly mounted or under-ducted.

Ducted vs. Ductless Range Hoods: An Honest Comparison

The choice between ducted and ductless (recirculating) hoods is often framed as a convenience decision. It is actually a performance decision with meaningful health consequences.

Factor	Ducted Hood	Ductless / Recirculating Hood
PM2.5 removal	Exhaust particles outdoors — effectively 100% removal	Carbon/charcoal filter captures some VOCs; does not reliably capture fine particles
NO2 removal	Exhaust gas — high removal when capture efficiency is good	Minimal. Activated carbon provides limited NO2 adsorption at typical concentrations
CO removal	Yes, exhausted outdoors	No meaningful CO removal
Moisture removal	Yes — exhausts steam and humidity	No — moisture is returned to the kitchen
Grease removal	Baffle/mesh filters capture grease; exhaust combustion aerosols	Grease filter plus charcoal filter; grease accumulates faster
VOC removal	Good — exhausted outdoors	Moderate — depends heavily on carbon filter freshness and mass
Installation complexity	Requires exterior duct penetration	No duct required; plug-in or standard wiring
Filter replacement	Grease filters only (washable baffle filters preferred)	Charcoal filters every 3–6 months; ongoing cost
Noise	Can use a remote blower to reduce kitchen noise significantly	Blower in unit; typically audible
Best application	Any kitchen where ducting is feasible — especially gas cooktops	Apartments, rentals, light electric cooking only

The verdict for gas cooktops is unambiguous: a ductless hood is not a suitable substitute. It returns moisture, cannot remove CO or NO2, and relies on carbon filters for VOCs that quickly become saturated. Ducted installation is the correct solution wherever structurally possible. For ductless-only situations, maximize the carbon filter’s mass, replace filters on schedule, and supplement with a window opening or a portable air purifier during cooking.

Summary: Ducted range hoods remove virtually all cooking pollutants by exhausting them outdoors. Ductless hoods recirculate air through filters that cannot capture NO2, CO, or moisture, providing only partial VOC removal. For gas cooktops, ducted installation is strongly recommended. Ductless hoods are acceptable options for light electric cooking when exterior ducting is structurally impossible.

Induction vs. Gas: How Your Cooktop Changes Your Ventilation Needs

The type of cooktop you use directly determines the types of pollutants your range hood must handle — and the minimum performance level required.

Gas Cooktops

Gas combustion produces NO2, CO, water vapor, and particulate matter regardless of what is being cooked. Even an idle gas burner emits measurable NO2. When cooking begins, these combustion byproducts combine with food-derived emissions (PM2.5, VOCs, grease aerosols). The result is a complex, multi-pollutant plume that requires genuine exhaust ventilation—not recirculation—to be managed safely. ASHRAE 62.2 recommends a minimum of 100 CFM of continuous or intermittent ventilation for kitchens with gas appliances. Many experts consider 200–400 CFM minimum to be the norm for typical residential gas cooking.

Electric Resistance Cooktops

Electric resistance burners eliminate combustion products. The remaining emissions are food-derived: PM2.5, VOCs, and grease aerosols from the cooking process itself. These are still meaningful pollution sources, particularly during high-heat cooking. Ventilation requirements are lower than for gas, but not negligible. A 200–400 CFM ducted hood remains a reasonable recommendation for regular cooking.

Induction Cooktops

Induction heating produces no combustion byproducts and emits less radiant heat, resulting in a weaker convective plume that rises more slowly. Food-derived PM2.5 and VOCs are still produced, but at generally lower total emission rates than gas. Capture is actually easier because the plume is less energetic. A well-placed 200–300 CFM hood is often sufficient for induction cooking. Some studies suggest that households switching from gas to induction and adding proper ventilation see substantial reductions in kitchen NO2 — reductions comparable to removing a gas appliance entirely.

Cooktop Type	Primary Pollutants	Minimum Recommended CFM	Ducted Essential?
Gas (residential)	NO2, CO, PM2.5, VOCs, moisture	200–400 CFM	Yes
Electric resistance	PM2.5, VOCs, grease aerosols	150–300 CFM	Strongly preferred
Induction	PM2.5, VOCs (food-derived only)	150–250 CFM	Preferred; ductless acceptable for light cooking

Summary: Gas cooktops require a minimum of 200–400 CFM ducted exhaust ventilation to remove combustion-derived NO2, CO, and moisture. Induction cooktops produce only food-derived pollutants, require lower airflow rates, and are more tolerant of well-maintained ductless solutions. Switching to induction and installing proper ventilation are among the highest-impact indoor air quality improvements available to homeowners.

Makeup Air: The Problem Nobody Tells You About Until It’s Too Late

Every CFM your range hood exhausts outdoors must be replaced by an equal volume of air coming in from somewhere. In a tight modern home, a powerful range hood can depressurize the kitchen, causing problems ranging from annoying to dangerous.

What Depressurization Does

• Backdrafting combustion appliances: A depressurized home can reverse the draft in a gas water heater, furnace, or fireplace flue, pulling combustion gases — including CO — back into the living space. This is not a theoretical risk. It is a documented cause of residential CO poisoning.
• Hood performance degradation: When makeup air cannot enter fast enough, the suction at the hood face drops, reducing actual airflow below rated capacity.
• Door and window binding: A well-sealed home under significant negative pressure makes doors difficult to open and can pull outside air through the least-controlled paths — wall penetrations, crawlspaces, and duct leaks — carrying moisture, radon, and pollutants.

The Threshold: 400 CFM

ASHRAE and the Home Ventilating Institute (HVI) recommend providing dedicated makeup air when a range hood exceeds 400 CFM in a tight, well-sealed home. In practice, this means:

• Hoods rated above 400 CFM in newer, well-insulated homes should be paired with a makeup air system — either a passive inlet damper or an active makeup air unit.
• Older, leaky homes have natural infiltration that partially compensates, but relying on this is not a controlled solution and introduces unfiltered outdoor air through uncontrolled paths.
• The simplest, most practical solution for most homeowners: run the hood at a lower speed setting (often 200–300 CFM delivered) and optimize placement and duct design so that lower speed delivers high capture efficiency. This avoids the makeup air problem entirely without sacrificing performance.

Summary: Range hoods exhausting more than 400 CFM in a tight home can depressurize the kitchen zone, risking backdrafting of gas appliances and CO intrusion. Dedicated makeup air is required above this threshold per ASHRAE guidelines. For most homeowners, optimizing hood placement and duct efficiency at moderate fan speeds is a simpler and equally effective solution.

How to Actually Measure Your Hood’s Performance

Buying a better hood is only one path to improvement. Measuring what you already have — and diagnosing where it fails — is often faster and cheaper.

Step-by-Step: Baseline Your Kitchen Air Quality

1. Install an air quality monitor at counter height, 3–5 feet (0.9–1.5 m) from the cooktop. Let it log baseline PM2.5 and VOC levels for 24 hours before any cooking test.
2. Cook a standardized test meal — pan-frying at medium-high heat for 10 minutes on a front burner with the hood off. Record peak PM2.5 reading.
3. Repeat with the hood running at its standard operating speed. Record peak PM2.5 and how quickly levels return to baseline after cooking ends.
4. Measure duct airflow at the wall or roof termination using a digital anemometer. Compare measured CFM to rated CFM. A gap larger than 25% points to duct resistance issues that need fixing.
5. Check for backdraft: With the hood running at high speed, hold a lit incense stick near the draft diverter on your water heater or furnace. If smoke is drawn downward, you have a backdrafting condition that requires immediate attention.

What Good Numbers Look Like

• PM2.5 peak during frying: ideally <35 µg/m³ with hood running (AQI “Good” threshold)
• Return to baseline PM2.5 within 15–20 minutes of cooking end
• Delivered CFM within 20% of the rated value
• No measurable negative pressure at interior doors (they should open and close normally)

Summary: Measuring your hood’s real-world performance with an air quality monitor and airflow meter takes under an hour and tells you more than any spec sheet. If peak PM2.5 exceeds 35 µg/m³ during cooking with the hood running, or if the delivered CFM is more than 25% below the rated CFM, the installation — not the unit — is likely the first problem to address.

Solution First: What to Do Now

1. Log current PM2.5 readings during and after cooking to set a real performance baseline.
2. Check and correct hood mounting height — 24–30 inches (61–76 cm) above the cooktop surface is the effective range for most residential hoods.
3. Inspect duct runs for flex duct kinking, undersized diameter, or excess elbows; replace with semi-rigid metal where possible.
4. Confirm the hood width meets or slightly exceeds the cooktop width; replace the baffle/mesh grease filters on schedule and check that they are not restricting airflow.
5. Install a backdraft damper on the exhaust duct if not already present; verify it opens freely under fan operation.
6. If cooking on gas, supplement with a window crack or passive makeup air inlet when running the hood on high; consider switching front burners to induction as an interim measure.
7. Reassess PM2.5 readings after each change; iterate until performance targets are met.

Recommended Gear: Tools and Upgrades That Make a Real Difference

These are not everyday products — they are the pieces of the system that most homeowners overlook entirely, yet they drive the largest improvements in actual performance. Ratings and review volumes were used to select each.

Product	What It Solves	Shop a Recommended Pick
Hauslane UC-PS38 Under-Cabinet Range Hood (950 CFM)	High-output ducted ventilation with baffle filters and variable speed; covers professional-grade cooking loads	See the Hauslane UC-PS38 on Amazon
Hauslane UC-PS18 Under-Cabinet Range Hood (30″)	Stainless baffle filter, 3-speed, LED lighting; strong delivered CFM for standard residential kitchens	See the Hauslane UC-PS18 on Amazon
ZLINE KB-30 Wall-Mount Chimney Hood (760 CFM)	Wide-body stainless design with dishwasher-safe baffle filters; pairs ducted performance with chimney aesthetics	See the ZLINE KB-30 on Amazon
Cosmo COS-668ICS750 Island Range Hood	Ceiling-mount island configuration for cooktops not against a wall; 380 CFM with baffle filters and halogen lighting	See the Cosmo Island Hood on Amazon
Broan-NuTone 413004 Under-Cabinet Hood	Proven budget performer; top-selling residential hood in the US with straightforward duct-or-ductless convertibility	See the Broan 413004 on Amazon
GoveeLife H5106 Air Quality Monitor (PM2.5, VOC, CO2)	Measures what your hood is actually doing; real-time PM2.5 and VOC data during cooking to verify capture performance	See the GoveeLife H5106 on Amazon
BTMETER BT-100APP Digital Anemometer (CFM + Bluetooth)	Measures actual delivered airflow at your duct termination; confirms whether rated CFM matches real performance	See the BTMETER BT-100APP on Amazon
FAMCO BD6 6″ Backdraft Damper	Prevents cold air intrusion and negative-pressure reversal through the exhaust duct when the hood is off	See the FAMCO BD6 on Amazon
Kasa Smart Plug EP25 with Energy Monitoring	Tracks the power consumption of the hood and cooking appliance; enables scheduling to avoid peak-rate electricity periods.	See the Kasa EP25 on Amazon

Key Points at a Glance

Main	Point
Core principle	Capture efficiency matters more than rated CFM — placement and ducting determine real performance.
Biggest risk	Gas cooktops without proper ducted exhaust generate NO2 and CO at levels that exceed health guidelines during normal cooking.
Best upgrade path	Measure first (air quality monitor + anemometer), fix duct issues second, upgrade hood third if needed.
Makeup air threshold	Homes with hoods above 400 CFM need makeup air; below this, optimize at lower speeds to avoid depressurization.
Ductless verdict	Acceptable for light induction cooking only; not a substitute for ducted exhaust on gas ranges.
Mounting height	24–30 in (61–76 cm) above the cooktop surface; every extra inch above this reduces capture by a meaningful amount.
Duct sizing rule	8-inch (20 cm) round minimum for hoods over 400 CFM; flex duct kinking is the most common cause of underperformance.
Target metrics	PM2.5 <35 µg/m³ during cooking, return to baseline within 20 min, delivered CFM within 20% of rated.

Experience-Based Advice

• Log PM2.5 before and during cooking runs with the hood on to verify actual capture — not assumed capture.
• Use semi-rigid metal duct (26-gauge galvanized or stainless) for all horizontal runs; flexible foil ducts collapse at bends and choke airflow.
• Tape duct joints with UL 181B-listed foil tape, not standard duct tape — it degrades quickly in grease-laden airflow.
• Wash baffle grease filters monthly in a dishwasher; clogged baffles can add static pressure and measurably reduce delivered CFM.
• Install a backdraft damper at the exterior wall cap and the hood collar — dual dampers are worth the cost in cold climates.
• Position the air quality monitor at counter height, not ceiling height, during cooking tests; pollutants are concentrated at breathing level before stratifying upward.
• On island hoods, add 6–9 inches (15–23 cm) to each side of the cooktop footprint when sizing — the plume from island burners encounters crossflow from all directions and spreads faster than wall-mounted configurations.
• If replacing a ductless hood with a ducted unit, increase duct diameter by one size over the minimum; the marginal cost is trivial compared to the retrofit cost of upgrading later.

Glossary (Clear Definitions)

• RH: Relative humidity — moisture content of air as a percentage of the maximum it can hold at that temperature. Target: 40–50% indoors (EPA).
• NO2: Nitrogen dioxide — a combustion byproduct from gas burners with well-documented respiratory health effects at typical cooking concentrations.
• VOC: Volatile Organic Compounds — gaseous chemicals off-gassed from heated oils, coatings, adhesives, and building materials.
• PM2.5: Fine particulate matter ≤2.5 micrometers in diameter. Penetrates deep into lung tissue. Ideally below 8 µg/m³ indoors (EPA guidance).
• CFM: Cubic feet per minute — the volumetric airflow rate of a fan or duct system.
• Capture Efficiency: The percentage of cooking pollutants intercepted by the hood before dispersing into the kitchen—the most important real-world performance metric.
• Capture Velocity: The minimum air speed at the hood face required to pull the cooking plume into the hood rather than allowing it to spill into the room.
• Static Pressure: Resistance to airflow in a duct system. Caused by elbows, undersized ducts, dampers, grease accumulation, and flex duct kinks.
• Makeup Air: Outdoor air intentionally supplied to replace air exhausted by a range hood, preventing depressurization.
• Backdrafting: Reversal of draft in a combustion appliance flue caused by negative pressure, pulling combustion gases into the home.
• ACH: Air changes per hour — the number of times all the air in a room is replaced within one hour.
• Baffle Filter: A metal filter with baffled channels that separates grease from exhaust airflow. Preferred over mesh filters for durability and low static pressure.
• CO: Carbon monoxide — colorless, odorless combustion byproduct. Hazardous at elevated concentrations; produced by gas appliances and incomplete combustion.
• BTU: British Thermal Unit — a measure of heat energy. High-BTU gas ranges (with a total output of 60,000 BTU or more) generally require higher CFM ventilation.
• Convective Plume: The rising column of hot air and combustion gases above a heating source—the primary vehicle carrying cooking pollutants toward the range hood.
• Infiltration: Uncontrolled outdoor air entering a home through unsealed gaps and cracks — the primary source of unintended makeup air in leaky homes.
• Off-gassing: Gradual emission of VOCs from materials such as nonstick coatings, adhesives, and food-contact plastics when heated.
• ASTM E3087: The standard test method for measuring residential range hood capture efficiency under realistic cooking conditions. The most meaningful performance benchmark available.
• Bypass Leak: Air that bypasses a filter by passing around the frame rather than through the filter media, reducing effective filtration.
• Pre-filter: A first-stage filter layer that captures coarse grease, dust, and hair before the main filter stage, extending primary filter life.

Targets to remember: RH 40–50% indoors (EPA); PM2.5 as low as practical, ideally below 8 µg/m³ indoors; ventilate when outdoor air is clean, filter when it is not.

Related Topics You May Find Helpful

Does cooking on a gas stove affect long-term lung health?

Yes, according to published research. Repeated exposure to NO2 at concentrations typical in poorly ventilated gas kitchens (200–400 ppb during cooking) is associated with reduced lung function in children and exacerbated asthma symptoms. A 2023 meta-analysis estimated that gas stove use contributes to approximately 12.7% of childhood asthma cases in the US. The American Lung Association specifically identifies gas cooking as a meaningful indoor air quality concern. The most direct mitigation is ducted ventilation, used consistently during every cooking event.

What is the best CFM range hood for a home kitchen with gas burners?

For a standard residential gas range (30,000–60,000 total BTU), a ducted range hood delivering 200–400 CFM at the cooktop is sufficient when correctly sized and mounted. The practical formula is 1 CFM per 100 BTU of total burner output for wall-mount hoods, and 1.5 CFM per 100 BTU for island configurations. A hood rated at 400–600 CFM, when properly ducted, will deliver 300–450 CFM in practice, which is the correct operating range. Choose a hood rated higher than your minimum so it reaches adequate performance at mid-speed settings, reducing noise and makeup air demand.

How do I know if my range hood is working properly?

The most direct test is measuring PM2.5 at counter height during a standardized cooking event with the hood running. A well-performing ducted installation should keep PM2.5 below 35 µg/m³ during frying and return levels to below 12 µg/m³ within 15–20 minutes of cooking ending. Secondary checks: hold a single sheet of paper at the hood face with the fan on — it should be held firmly against the grille at medium speed. Listen for rattling that signals loose duct connections. Measure duct airflow with an anemometer and confirm it is within 20% of the rated CFM.

Can a range hood reduce exposure to natural gas from cooking?

Yes — and this is an increasingly important context. Recent studies using residential air sampling detected methane and benzene leaking from gas burners even when the burners were not in use. During cooking, a ducted range hood running before ignition and for 5–10 minutes after cooking ends is effective at capturing and exhausting combustion gases, including benzene, formaldehyde, and toluene that would otherwise accumulate in kitchen air. Running the hood before lighting the burner — not after the plume has already formed — meaningfully improves capture of the initial combustion burst.

What should I check before replacing a range hood?

Before buying a new hood, diagnose the installation first. In most cases, underperforming residential range hoods fail because of: (1) flex duct that has kinked or collapsed since installation, (2) a grease-clogged mesh filter adding substantial static pressure, (3) mounting height creeping above 30 inches (76 cm) due to cabinet soffits, or (4) an undersized duct diameter that was acceptable at original rated CFM but cannot support an upgraded blower. Fixing these issues costs less than a replacement hood and frequently restores adequate performance. Only after confirming a clean, correctly sized duct run should you evaluate whether the hood body itself is the limiting factor.

Is an induction cooktop significantly better for indoor air quality than a gas cooktop?

For combustion-derived pollutants — NO2 and CO specifically — the answer is yes, substantially. Eliminating the gas flame removes the primary source of these gases in the kitchen. Studies comparing paired gas and induction kitchens have documented reductions in kitchen NO2 of 35–55% when switching to induction with equivalent ventilation. Food-derived PM2.5 and VOCs remain, but at lower total levels due to the cooler cooking surface and reduced thermal plume energy. For households with children, asthma, or other respiratory concerns, the induction switch combined with ducted ventilation represents the greatest single-step improvement available.

FAQ

How high should a range hood be mounted above the cooktop?

The effective range is 24–30 inches (61–76 cm) above the cooking surface for most residential under-cabinet and wall-mount hoods. Below 24 inches, grease can damage the hood body; above 30 inches, the convective plume widens and spills before being captured. For professional-style high-BTU ranges (over 60,000 BTU total), some manufacturers specify 26–28 inches (66–71 cm) to capture the faster-rising, more energetic plume. Always follow the specific manufacturer height recommendation as the primary source, using the 24–30 inch range as the general boundary.

What duct size is required for a 600 CFM range hood?

A 600 CFM range hood requires a minimum of a 7-inch (17.8 cm) round duct, but an 8-inch (20.3 cm) round duct is the practical recommendation for any run over 8 feet (2.4 m) or with more than one elbow. Using a 6-inch (15.2 cm) duct with a 600 CFM hood adds substantial static pressure, reducing the delivered airflow to approximately 350–450 CFM—a 25–40% loss. Rectangular duct equivalents: 8-inch round ≈ 3.25 × 10-inch rectangular in cross-sectional area.

Do range hood carbon filters actually remove cooking smells and VOCs?

Yes, when fresh, well-specified, and correctly sized. Activated carbon adsorbs VOCs, including cooking odors, some formaldehyde, and certain other gaseous pollutants through surface adhesion. The critical variables are carbon mass (more is significantly better), airflow rate (high flow reduces contact time and adsorption efficiency), and filter age (carbon saturates and must be replaced every 3–6 months under regular cooking). A charcoal filter with less than 2 oz (56 g) of carbon provides minimal real-world VOC removal at typical hood airflow rates. Filters do not remove PM2.5, NO2, CO, or moisture.

Can a powerful range hood pull CO from a gas water heater into my kitchen?

Yes — this is the backdrafting hazard described above, and it is the primary safety reason makeup air matters. A range hood exhausting 400+ CFM in a tight home can create enough negative pressure to reverse the natural draft in the flue of a gas water heater, furnace, or fireplace insert. The result is that combustion gases — including CO — are pulled into the living space rather than venting outdoors. The test is simple: with the hood on high, hold a smoke source near the draft diverter on the water heater. If the moke goes down, depressurization is occurring. Solutions include adding a makeup air inlet or running the hood at lower speeds.

How often should range hood filters be cleaned or replaced?

Baffle and mesh grease filters should be cleaned monthly for daily cooking or every 2–3 months for occasional use. Most baffle filters (stainless or aluminum) are dishwasher-safe; standard mesh filters should be soaked in a hot degreaser solution. A clogged grease filter adds static pressure, reducing delivered CFM and creating a fire hazard. Charcoal/carbon filters in ductless hoods are not washable and should be replaced every 3–6 months; saturated carbon filters provide no meaningful VOC removal and should not be left in service.