Kitchen HVAC Modifications
Proper ventilation is critical in kitchens. Your range hood needs exterior venting, and layout changes may require relocating heating and cooling vents. Getting this right ensures comfort, air quality, and safety.
Quick Summary
Timeline
1-3 days
Hood venting cost
$500-2,000
Make-up air system
$1,500-4,000
Range Hood Venting: The Most Critical HVAC Element
A properly vented range hood removes cooking fumes, smoke, grease, and moisture. Recirculating (ductless) hoods filter air but don't remove it—exterior venting is always better for air quality.
Vented vs. Recirculating: Vented hoods exhaust air outside. Recirculating hoods filter and return air to the room. Vented is always more effective—it removes heat, moisture, and pollutants. Use recirculating only when exterior venting is impossible.
Determining CFM Requirements
CFM (cubic feet per minute) measures how much air the hood moves. The right CFM depends on your range type, cooking style, and kitchen size.
| Range Type | Recommended CFM | Notes |
|---|---|---|
| Standard electric | 200-300 CFM | Lower heat, less exhaust needed |
| Standard gas (30") | 300-400 CFM | Typical residential range |
| Induction | 250-350 CFM | Efficient, less heat waste |
| Pro-style gas (36") | 600-900 CFM | Higher BTU output |
| Pro-style gas (48"+) | 900-1200+ CFM | Often requires make-up air |
Quick CFM Calculation for Gas Ranges
Take total BTU output and divide by 100. A 60,000 BTU range needs at least 600 CFM. Add more for high-heat cooking styles (wok cooking, frequent frying) or hoods mounted higher than 30 inches above the cooktop.
Range Hood Installation Process
Plan the Duct Route
The best duct route is short and straight. Every turn reduces efficiency. Plan before walls close—it's much harder to route ductwork after drywall is up.
Ideal Routing
- • Straight up through roof
- • Straight out through exterior wall
- • One or fewer elbows
- • Under 25 feet total length
Avoid If Possible
- • Multiple elbows (each reduces CFM)
- • Long horizontal runs
- • Downward runs (grease collects)
- • Flexible duct (fire hazard)
Size the Ductwork
Duct diameter affects airflow. Undersized ductwork reduces hood performance and increases noise. Match duct size to hood CFM.
Pro tip: Never reduce duct size below what the hood manufacturer specifies. Use rigid smooth-wall metal duct, not corrugated or flexible—they restrict airflow and collect grease.
Install the Exterior Cap
The exterior cap is where the duct exits your home. It needs a backdraft damper to prevent air from entering when the hood is off, and proper weatherproofing.
Cap Options
- Wall cap:Most common. Installs on exterior wall. Easier to clean and maintain.
- Roof cap:Used when wall venting isn't possible. Requires proper roof penetration and flashing.
- Soffit vent:Exits through soffit. Works but not ideal—heat rises and can damage soffit over time.
Seal All Connections
Leaky duct connections reduce efficiency and can deposit grease in wall or ceiling cavities—a fire hazard. Seal every joint.
Proper sealing method: Use foil tape (not cloth duct tape) on all joints, then apply duct mastic over the tape. Screws alone aren't enough—air will leak through screw holes without mastic.
Make-Up Air: What It Is and Why You Might Need It
Powerful range hoods remove large volumes of air from your home. That air has to be replaced somehow. In newer, tightly sealed homes, this can create problems—and code often requires a make-up air system.
Problems Without Make-Up Air
- Negative pressure makes doors hard to open
- Fireplace and water heater backdrafting
- Carbon monoxide entering the home
- Range hood performs poorly
- Whistling through cracks and gaps
When Make-Up Air Is Required
- Hoods over 400 CFM (varies by code)
- Newer, tightly sealed homes (2010+)
- Homes with sealed combustion appliances
- When local code mandates it
- Passive house or high-performance homes
Make-Up Air System Options
- Passive damper:Opens automatically when hood runs. Brings in outdoor air. Cheapest option ($200-500).
- Powered system:Fan actively brings in outside air when hood activates. Better for very tight homes ($1,500-3,000).
- Conditioned air:Ties into HVAC to temper incoming air. Prevents cold drafts in winter ($2,500-4,000+).
Relocating Heating and Cooling Vents
If your kitchen layout changes significantly, you may need to move floor registers, wall vents, or return air grilles. This ensures proper heating and cooling in the remodeled space.
Cost expectation: Moving a floor register typically costs $150-400. Rerouting ductwork for major changes runs $500-1,500 depending on complexity.
Common HVAC Mistakes
Using flexible duct for range hoods
Flex duct is a fire hazard for range exhaust—it collects grease and restricts airflow. Always use rigid metal duct.
Undersized ductwork
Duct that's too small makes the hood noisy and ineffective. Match duct diameter to hood CFM requirements.
Ignoring make-up air requirements
Powerful hoods without make-up air can cause backdrafting, bringing combustion gases into your home. Check code requirements.
Venting into attic or wall cavity
Never terminate range exhaust inside the building envelope. Grease buildup is a fire hazard and moisture causes mold. Always vent to exterior.
Frequently Asked Questions
How many CFM does my range hood need?
Standard residential ranges need 200-400 CFM. For gas ranges, divide total BTU by 100 (60,000 BTU = 600 CFM minimum). Pro-style ranges often need 600-1200+ CFM. Consider your cooking style too—heavy frying or wok cooking benefits from higher CFM.
Can I use flexible duct for my range hood?
No. Flexible duct is a fire hazard for range hoods because it collects grease and restricts airflow. Code requires rigid or semi-rigid metal duct. Use smooth-wall galvanized or aluminum duct with minimal elbows.
What is make-up air and do I need it?
Make-up air replaces air exhausted by your range hood. In tight modern homes, powerful hoods (400+ CFM) create negative pressure that can cause backdrafting, difficulty opening doors, and poor hood performance. Many codes require make-up air for high-CFM hoods.
Wall venting vs. roof venting—which is better?
Wall venting is usually preferred—it's easier to install, easier to clean, and less prone to roof leaks. Roof venting works when there's no exterior wall access. Choose the shortest, straightest route regardless of termination point.
Ready for the Next Step?
With all rough-in work complete and inspected, it's time to close up the walls with drywall and prepare for cabinets. The structural phase is nearly complete!