Kitchen Ventilation

Homeowner Summary

Kitchen ventilation is one of the most underappreciated systems in a home. A properly sized and functioning range hood removes cooking byproducts -- smoke, steam, grease particles, odors, and (critically for gas cooktops) combustion gases including carbon monoxide, nitrogen dioxide, and formaldehyde -- before they spread through the home and degrade indoor air quality.

Studies have shown that cooking on a gas stove without ventilation can produce indoor nitrogen dioxide levels that exceed EPA outdoor air quality standards. Even electric cooking generates particulate matter and volatile organic compounds that affect air quality. Adequate kitchen ventilation is a health consideration, not just a comfort feature.

Range hoods come in two fundamental types: ducted (vented to the outside) and ductless (recirculating through filters). Ducted hoods are dramatically more effective because they physically remove contaminants from the home. Ductless hoods filter odors and some grease but cannot remove heat, moisture, or combustion gases. For any home with a gas cooktop, ducted ventilation is strongly recommended.

How It Works

Ducted Range Hoods

1. Capture zone -- The hood canopy is positioned above the cooktop to capture rising cooking fumes, heat, and moisture. Wider canopies and lower mounting heights improve capture efficiency.
2. Grease filtration -- Incoming air first passes through grease filters (aluminum mesh, baffle, or stainless steel). These trap airborne grease to prevent it from accumulating in the ductwork and fan.
3. Fan/blower -- A centrifugal or axial fan (measured in CFM -- cubic feet per minute) pulls air through the filters and pushes it into the ductwork.
4. Ductwork -- Rigid metal ducts carry the contaminated air from the hood to the building exterior. The shorter and straighter the duct run, the more effective the exhaust.
5. Exterior termination -- A wall cap or roof cap with a damper prevents outside air, pests, and weather from entering the duct when the hood is off.

Ductless (Recirculating) Range Hoods

Same as above except there is no ductwork. After grease filtration, the air passes through an activated charcoal filter to absorb odors, then is blown back into the kitchen. Ductless hoods:

• Remove odors (partially, until the charcoal is saturated)
• Remove some grease particles
• Do NOT remove heat, moisture, CO, NO2, or other combustion gases
• Are significantly less effective than ducted systems
• Should only be used when ducted installation is truly impossible

Hood Types

| Type | Description | CFM Range | Best For | |------|-------------|-----------|----------| | Under-cabinet | Mounts beneath wall cabinets above the range | 150-600 CFM | Most common residential installation | | Wall-mounted chimney | Mounts to the wall, exposed chimney-style duct cover | 300-1,200 CFM | Kitchens without upper cabinets above the range | | Island hood | Mounts to the ceiling above an island cooktop | 400-1,500 CFM | Kitchen islands (requires more CFM due to cross-drafts) | | Downdraft | Rises from behind/beside the cooktop or is built into it | 300-600 CFM | Island cooktops where ceiling mounting isn't feasible | | Over-the-range microwave | Combination microwave and ventilation | 200-400 CFM | Budget option; limited ventilation performance | | Insert/liner | Fan and filter module inserted into a custom hood enclosure | 300-1,200 CFM | Custom kitchen designs |

CFM Sizing

CFM (cubic feet per minute) measures airflow capacity. Proper sizing depends on the cooking equipment and kitchen configuration:

For gas cooktops: The standard formula is 1 CFM per 100 BTU of total burner output. For example, a gas range with four burners totaling 55,000 BTU needs a minimum 550 CFM hood.

For electric/induction cooktops: The standard formula is 10 CFM per inch of cooktop width. A 30-inch cooktop needs at least 300 CFM.

Adjustments:

• Island installations: Increase CFM by 50% (no wall to help contain fumes).
• Duct length/elbows: Each additional foot of duct beyond 10 feet and each elbow reduces effective CFM. Manufacturers provide derating tables.
• Hood mounting height: Standard 24-30 inches above the cooktop. Every additional inch above 30 reduces capture efficiency significantly.
• Professional-style ranges (30,000+ BTU burners): Often require 600-1,200 CFM hoods.

Minimum recommendations:

• Electric cooktop: 300 CFM minimum, 400+ CFM recommended
• Gas cooktop: Match BTU output (1:100 ratio), minimum 400 CFM
• Pro-style gas: 600-1,200 CFM based on BTU rating
• Island installation: 50% more than wall-mounted equivalent

Maintenance Guide

DIY (Homeowner)

• Clean or replace grease filters monthly. Aluminum mesh filters: soak in hot water with dish soap and baking soda for 15-30 minutes, scrub gently, rinse, and air dry. Many are dishwasher-safe (check the manual). Baffle filters: remove and soak in degreaser solution, scrub, rinse. Replace mesh filters when they are damaged, discolored, or no longer clean effectively (typically every 1-3 years depending on cooking frequency).
• Replace charcoal filters every 3-6 months (ductless hoods). Charcoal filters cannot be cleaned. When saturated, they stop absorbing odors. Mark the installation date on the filter.
• Wipe the hood exterior and interior monthly. Use a degreaser or a mixture of dish soap and warm water. Grease accumulates on surfaces and can become a fire hazard over time. Stainless steel hoods benefit from stainless-specific cleaners.
• Clean the fan blades annually. With the power off, access the fan (usually by removing the filters and the fan cover). Wipe grease and dust from the blades. Heavy grease buildup reduces airflow and causes imbalance/noise.
• Test the light(s) and fan speeds. Ensure all fan speeds work and the lighting illuminates the cooktop. Replace burned-out bulbs promptly.
• Check the exterior vent cap. Ensure the damper opens and closes freely, and that the opening is not blocked by debris, bird nests, or ice.
• Use the hood every time you cook. Many homeowners install a range hood and then don't use it consistently. Run the hood on an appropriate speed setting from the time you start cooking until several minutes after you finish. This is especially important for gas cooking.

Professional

• Annual ductwork inspection: Check for grease accumulation, disconnections, or damage inside the ductwork. Professional duct cleaning may be needed in high-use kitchens (restaurants require this quarterly; residential typically every 3-5 years if properly filtered).
• Fan motor assessment: Check motor bearings, amp draw, and vibration. Lubricate bearings if applicable.
• Airflow verification: Measure actual CFM output at the hood face using an anemometer or balometer. Compare against rated CFM. Significant reduction indicates duct blockage, filter clogging, or fan degradation.
• Makeup air system inspection (if installed): Verify damper operation, airflow balancing, and control integration with the hood.
• Electrical connections: Check wiring, switches, and control board (for electronic hoods with auto-sensing features).

Warning Signs

• Lingering cooking odors throughout the house -- Hood CFM is insufficient, ductwork is blocked, or the hood is not being used.
• Visible grease on cabinets or walls near the cooktop -- Hood is undersized, mounted too high, or filters are clogged/bypassed.
• Condensation on kitchen windows during cooking -- Moisture is not being exhausted effectively.
• Fan noise has increased -- Grease buildup on fan blades, worn motor bearings, or obstructed ductwork causing the fan to work harder.
• Fan runs but doesn't seem to pull air -- Ductwork disconnection, crushed duct, blocked exterior vent, or failed damper.
• Grease dripping from the hood -- Severely overdue filter cleaning or a damaged filter allowing grease past the filtration stage.
• Headaches or irritation during gas cooking -- Inadequate ventilation allowing combustion byproducts to accumulate. This is a health concern requiring immediate attention.
• Hood light flickering or fan speeds not working -- Switch, control board, or wiring issue.

When to Replace vs Repair

Range hoods are mechanically simple, and many issues are maintenance-related rather than true failures.

| Age | Recommendation | |-----|---------------| | 0-7 years | Repair or maintain. Most issues are filter cleaning, light bulbs, or switch replacements. | | 7-12 years | Repair for motor, switch, or fan issues (typically $100-250). Consider upgrading if the hood is undersized for the cooktop. | | 12-15 years | Repair only for simple fixes. If upgrading the cooktop or kitchen, replace the hood to match. | | 15+ years | Replace. Modern hoods are quieter, more powerful, and more energy-efficient. Ductwork may need cleaning or replacement at this age. |

Always replace if:

• The hood is undersized for the cooktop (especially if upgrading from electric to gas or adding a pro-style range).
• The hood is ductless and you have a gas cooktop (upgrade to ducted).
• The fan motor has failed on a unit over 10 years old.
• Grease has significantly accumulated inside the ductwork (replace both hood and ductwork).

Upgrade opportunities:

• Switching from a recirculating OTR microwave to a proper ducted range hood is one of the highest-impact indoor air quality improvements available. This is a strong dealer recommendation for any kitchen with a gas range.

Pro Detail

Specifications & Sizing

• Hood width: Should be at least as wide as the cooktop, ideally 3-6 inches wider on each side for better capture. A 30-inch range should have at minimum a 30-inch hood (36-inch preferred).
• Mounting height: 24-30 inches above the cooktop surface (gas). 20-24 inches for electric. Lower is more effective but must not impede cooking. Follow manufacturer specifications.
• Duct sizing:
  • Under 400 CFM: 6-inch round or 3.25 x 10-inch rectangular
  • 400-900 CFM: 8-inch round or equivalent rectangular
  • 900-1,200 CFM: 10-inch round
  • 1,200+ CFM: 10-12 inch round or dual 8-inch runs
• Duct material: Rigid smooth-interior galvanized steel or stainless steel. Semi-rigid aluminum is acceptable for short runs. Flexible duct is not recommended (high friction loss, grease accumulation, difficult to clean).
• Duct transitions: Every 90-degree elbow adds approximately 10 feet equivalent length. Every 45-degree elbow adds 5 feet. Minimize transitions for best performance.
• Maximum duct run: Varies by CFM and duct size. Typical maximum for a 400 CFM hood with 6-inch duct: 30 feet equivalent length (including elbows). Consult manufacturer documentation.
• Sone ratings (noise):
  • Quiet: 1-3 sones (comfortable background noise)
  • Moderate: 4-6 sones (noticeable but acceptable)
  • Loud: 7-10 sones (conversation becomes difficult)
  • Very loud: 10+ sones (common in high-CFM pro hoods)
  • Remote blowers (mounted in the ductwork or on the roof) can reduce in-kitchen noise by 50%+.

Makeup Air Requirements

This is one of the most important -- and most frequently overlooked -- aspects of kitchen ventilation design.

The problem: A powerful range hood exhausting 400+ CFM creates significant negative pressure inside the home. This can:

• Backdraft gas water heaters, furnaces, and fireplaces (pulling combustion gases into the home -- a life-safety hazard)
• Make exterior doors hard to open
• Draw air through unintended paths (sewer vents, attic, crawlspace) bringing in odors, moisture, or contaminants
• Reduce the hood's effective airflow (it can't exhaust air that it can't pull in)

The solution: Makeup air -- a dedicated supply of outdoor air to replace the air being exhausted.

Code requirements (IRC M1503.6 / IMC 508):

• Any exhaust system exceeding 400 CFM requires a makeup air system in most jurisdictions
• The makeup air volume must approximately equal the exhaust volume
• Makeup air must be automatically controlled (interlocked with the exhaust system)
• Makeup air may need to be tempered (heated or cooled) to maintain comfort

Makeup air types:

• Passive damper: A motorized damper in the exterior wall that opens when the hood runs, allowing outside air to flow in naturally. Simplest and cheapest but doesn't temper the air.
• Powered makeup air unit: A fan and damper (with optional heating element) that pushes conditioned air into the home when the hood operates. More effective, especially in cold climates.
• HVAC integration: Some systems tie into the HVAC ductwork to distribute makeup air throughout the home.

Common Failure Modes

| Component | Typical Failure Age | Symptoms | Repair Cost | |-----------|-------------------|----------|-------------| | Fan motor | 8-15 years | Won't run, slow speed, loud humming | $100-300 | | Motor bearings | 7-12 years | Grinding noise, vibration | $75-200 | | Speed switch/control | 5-10 years | Some speeds don't work | $50-150 | | Light socket/switch | 5-10 years | Lights won't work | $30-100 | | Damper (exterior cap) | 5-10 years | Stuck open (drafts) or closed (no exhaust) | $30-75 | | Makeup air damper | 5-10 years | Stuck open (energy waste) or closed (negative pressure) | $75-200 | | Control board (electronic) | 7-12 years | Erratic, unresponsive, auto-features fail | $100-300 | | Ductwork joint failure | 10-20 years | Grease leak, exhaust in wall/ceiling cavity | $150-400 | | Wiring/connection | Varies | Intermittent operation, no power | $50-150 |

Diagnostic Procedures

1. Low airflow. With the hood on high, hold a tissue or piece of plastic wrap near the filter face -- it should be sucked firmly against the filter. If suction is weak: check for clogged filters, obstructed ductwork, blocked exterior vent, or a failing fan motor. Measure CFM if possible.
2. Fan won't run. Verify power at the outlet or junction box. Test the switch or control board. Test the motor by applying direct power (bypass the switch). Check capacitor (if applicable). Listen for humming (seized motor) vs silence (no power or open winding).
3. Excessive noise. Identify the noise type: rattling (loose filter, loose duct connection, foreign object), grinding (motor bearings), whistling (undersized duct or restriction), vibration (unbalanced fan blade from grease buildup).
4. Backdrafting at other appliances. Turn on the range hood at maximum speed. Check all combustion appliances (water heater, furnace) for proper draft using a smoke pencil or match at the draft hood. If smoke is pulled back into the room, the home needs makeup air.
5. Makeup air system verification. With the hood running, verify the makeup air damper opens. Measure airflow at the makeup air inlet. It should approximately match the exhaust CFM. Test the interlock -- the makeup air should activate and deactivate with the hood.

Code & Compliance

• IRC M1503.4: Kitchen exhaust must terminate to the outdoors. Exhaust must not terminate in an attic, crawlspace, garage, or wall cavity.
• IRC M1503.6 / IMC 508: Makeup air required when exhaust capacity exceeds 400 CFM. Makeup air must be automatically controlled and approximately equal to exhaust volume.
• IRC G2407 / IFGC 304: Combustion air requirements for gas appliances. A powerful range hood can deplete combustion air for a gas furnace or water heater, requiring additional combustion air provisions.
• UL 507 / UL 710: Range hoods must be listed and labeled by a recognized testing laboratory.
• Clearance to combustibles: Minimum 24 inches from cooktop surface to bottom of a combustible hood (30 inches typical). Listed range hoods may have reduced clearances per the manufacturer's installation instructions.
• Fire suppression: Not required for residential range hoods (required for commercial kitchens per NFPA 96). However, a properly maintained grease filter is an important fire safety measure.
• NEC: Range hoods must be on a dedicated circuit or a shared kitchen circuit per local requirements. GFCI protection required if within 6 feet of a sink (varies by jurisdiction).
• ASHRAE 62.2: Requires minimum ventilation in residential kitchens. Intermittent local exhaust (range hood): 100 CFM minimum or continuous: 5 ACH (air changes per hour) in the kitchen.

Cost Guide

| Item | Typical Cost | Notes | |------|-------------|-------| | Grease filter replacement | $15-40 | Per filter; every 1-3 years | | Charcoal filter replacement | $10-30 | Ductless hoods; every 3-6 months | | Under-cabinet hood (basic) | $200-400 | Plus installation $150-300 | | Under-cabinet hood (mid-range) | $400-800 | Better motors, lower noise | | Wall-mount chimney hood | $500-1,500 | Plus installation $200-500 | | Island hood | $800-2,000+ | Plus ceiling duct installation $500-1,500 | | Insert/liner (custom hood) | $500-1,500 | Plus custom enclosure fabrication | | Professional-grade hood | $1,500-3,000+ | For pro-style ranges | | Ductwork installation (new) | $300-1,000 | Depends on run length and complexity | | Makeup air damper (passive) | $200-500 | Installed, including wall penetration | | Makeup air unit (powered) | $1,000-3,000 | With tempering; installed | | Fan motor replacement | $100-300 | Common repair | | Remote blower | $400-800 | Inline or roof-mounted; reduces kitchen noise |

Energy Impact

• Fan energy: A range hood running at 400 CFM uses approximately 100-200 watts. Running 1-2 hours per day costs roughly $5-15/year in electricity -- negligible.
• The real energy cost is conditioned air loss. At 400 CFM, the hood exhausts conditioned air at a rate that equals the output of a small furnace or air conditioner. In heating season, exhausting 400 CFM of 70 degrees F air when it's 30 degrees F outside costs approximately $0.50-1.00/hour in heating energy (varies by fuel type and efficiency).
• Makeup air energy. Introducing unconditioned outdoor air requires tempering. A makeup air heater for a 600 CFM system in a cold climate can draw 3,000-10,000 watts. This is a significant operating cost but is required for safety and comfort.
• Strategies to minimize energy impact:
  • Use the minimum effective fan speed (low for simmering, high for high-heat cooking)
  • Turn the hood off shortly after cooking ends (but run it a few minutes post-cooking)
  • Use a variable-speed or multi-speed hood rather than single-speed
  • Consider a heat recovery ventilator (HRV) for makeup air in cold climates (recovers 60-80% of heat)
  • Ductless hoods use less energy overall (no conditioned air loss) but sacrifice air quality -- not recommended as a solution for energy savings when air quality matters
• Auto-sensing hoods use temperature and/or smoke sensors to activate automatically and adjust speed based on cooking intensity. These optimize the balance between ventilation effectiveness and energy use.

Shipshape Integration

• Indoor air quality monitoring: SAM integrates with indoor air quality sensors to detect elevated levels of particulate matter, VOCs, CO, and NO2 during cooking. If levels exceed health thresholds and the range hood is not running (or is running but insufficient), SAM sends an alert to the homeowner recommending ventilation use or upgrade.
• Maintenance reminders: Monthly grease filter cleaning reminders, charcoal filter replacement reminders (for ductless systems), and annual professional inspection reminders for ductwork and fan motor.
• Ventilation adequacy assessment: SAM evaluates the hood CFM relative to the installed cooktop (type and BTU rating) and flags homes where the ventilation is undersized. This is especially important when homeowners upgrade their cooktop without upgrading the hood.
• Makeup air intelligence: For homes with high-CFM hoods (400+ CFM), SAM checks for makeup air provisions and alerts dealers when a home may be at risk for combustion appliance backdrafting.
• Replacement forecasting: SAM tracks hood age and condition, recommending replacement when the unit approaches end of life or when kitchen upgrades create a mismatch between the cooktop and ventilation system.
• Home Health Score impact: Kitchen ventilation has a significant impact on the Indoor Air Quality subscore, especially in homes with gas cooking. Proper ducted ventilation, regular filter maintenance, and adequate CFM for the cooktop all improve the score. Ductless hoods with gas ranges reduce the score. Missing or non-functional ventilation is flagged as a health concern.
• Dealer actions: Dealers can assess ventilation adequacy during service visits, recommend hood upgrades (ductless to ducted, undersized to properly sized), note ductwork condition, identify makeup air needs, and document ventilation configuration for the home profile. Kitchen ventilation upgrades are a high-value service opportunity, especially paired with cooktop upgrades.