How to Install a Range Hood Exhaust Duct

A range hood is only as good as the duct behind it. You can buy the most powerful hood on the market, but if the exhaust path is undersized, poorly sealed, or twisted with unnecessary bends, smoke and grease will still hang around your kitchen. The duct is the part nobody thinks about until it fails, and by then you are usually looking at weak airflow, grease stains on the ceiling, or a failed inspection.

Getting this right matters even more in a commercial setting, where fire marshals and health inspectors expect exhaust systems built to exact specifications. Restaurant owners in the area rely on CRS Hoods for Commercial Hood Installation in Newark precisely because a single mistake in the ductwork can shut down a kitchen until it is corrected, and getting it right the first time saves both time and money.

Below is a practical walkthrough of what goes into a proper exhaust duct installation, along with the mistakes that trip people up most often.

What Makes a Good Exhaust Duct System

Before picking up any tools, it helps to understand what separates a duct system that works well from one that quietly underperforms for years. Three factors matter more than anything else: the material, the path, and the seal.

Metal duct with smooth interior walls moves air far more efficiently than flexible foil duct. A shorter, straighter path outperforms a long run full of turns. And a fully sealed system keeps grease laden air inside the pipe instead of leaking into your walls or ceiling. Get these three things right and the rest of the installation tends to fall into place.

Selecting the Right Duct Material

Rigid metal duct is the standard choice for most installations. Its smooth walls let air pass through with minimal resistance, and it holds up against heat and grease far better than softer materials.

Semi-rigid duct offers a middle ground. It flexes enough to work around minor obstacles while still outperforming fully flexible options.

Flexible foil duct is common in budget hood kits because it is cheap and easy to install, but its ridged interior chokes airflow. Most commercial kitchen codes do not allow it for grease duct runs, and even in residential settings it should be limited to very short distances.

Gathering What You Need

• Rigid or semi-rigid metal ductwork sized to match the hood outlet

• A roof or wall vent cap with a built in backdraft damper

• Metal duct tape or mastic sealant

• Sheet metal screws

• Jigsaw or hole saw

• Stud finder

• Level and tape measure

• Exterior grade caulk

• Ladder, safety glasses, and gloves

Installing the Duct, Start to Finish

Map the route first. Walk through the space and decide the shortest, straightest path between the hood and the outside of the building. Every bend you add costs you airflow, so a route with one gentle turn will always outperform one with three sharp corners.

Decide on wall or roof venting. A range against an exterior wall usually makes wall venting the simplest option. Island hoods or ranges positioned away from an outside wall typically need roof venting instead, which is a bigger job and often calls for a licensed contractor familiar with roof flashing.

Confirm the correct duct diameter. Check the hood's manual for the required outlet size and match your ductwork to it. A duct that is even slightly undersized will bottleneck the entire system.

Cut a clean opening. Locate studs or joists first so you avoid cutting into framing or wiring, then cut the opening for the duct using a jigsaw or hole saw.

Assemble the sections in the direction of airflow. Slide each upstream section into the downstream one so condensation and grease drain forward instead of pooling at a seam. Fasten with sheet metal screws.

Seal every single joint. Skip the cloth duct tape entirely and use metal foil tape or mastic sealant instead. This is the step most people rush, and it is also the one that determines whether grease stays inside the duct or ends up inside your walls.

Support long runs. Add hanger straps every few feet on longer sections to stop the duct from sagging, since a sagging section creates a low point where grease and moisture collect over time.

Mount the exterior vent cap. Install it with the backdraft damper facing the correct direction, then caulk thoroughly around the outside edge to keep water out.

Connect everything to the hood. Attach the top of the duct run to the hood's outlet collar, using a transition piece if the shapes do not match, and seal this final connection just as carefully as the rest.

Verifying the System Actually Works

Once everything is connected, turn the hood on and check the exterior vent for steady airflow. Holding a strip of tissue paper near the outside cap is an easy way to confirm air is moving out. While the fan runs, run your hand along each interior joint to feel for escaping air, since even a small leak will reduce performance over time and slowly deposit grease outside the duct itself.

Listen closely too. Rattling, whistling, or excess vibration usually points to a loose connection, a sagging section, or something obstructing the duct.

Pitfalls That Undermine Performance

• Choosing flexible foil duct for anything beyond a very short run

• Routing the duct through more bends than necessary

• Relying on screws alone without sealing the seams

• Leaving long duct sections unsupported

• Skipping the backdraft damper, which lets outside air and pests in when the fan is off

• Sizing the duct too small for the hood's actual output

Why Commercial Kitchens Need a Stricter Approach

Residential kitchens have some flexibility in materials and routing, but commercial kitchens do not. Health departments and fire marshals typically require welded black iron or stainless steel grease ducts, specific clearances from combustible materials, and access panels built in for routine cleaning. An improperly built commercial duct system is one of the most common reasons kitchens fail inspection, and it is not something most restaurant owners want to troubleshoot on their own.

This is exactly the gap that a specialized team fills. Businesses across the region turn to CRS Hoods for Commercial Hood Installation in Newark because the team understands the code requirements inspectors are checking for, not just how to run a pipe from point A to point B.

Wrapping Up

A range hood is only ever as effective as the duct connected to it. Take the time to plan a short, straight route, choose the right material, and seal every joint completely, and your hood will perform the way it was designed to. For a home kitchen, this is a project a careful do it yourselfer can usually manage in a weekend. For a commercial kitchen, where inspections and fire safety are non negotiable, bringing in a team that installs these systems every day is the safer bet.

Frequently Asked Questions

1. What size duct do I need for a range hood?

Match the duct to the outlet size listed in your hood's installation manual. Going smaller than that recommendation will bottleneck airflow no matter how strong the fan is.

2. Is flexible duct okay to use for a range hood exhaust?

It can work for very short residential runs, but its ridged interior slows airflow noticeably. Longer runs and any commercial kitchen should use rigid or semi-rigid metal duct instead, which most codes require anyway.

3. How many bends can an exhaust duct have before it hurts performance?

There is no fixed number, but every bend adds resistance. Stay within the equivalent length your hood manufacturer recommends, and use wide sweeping turns rather than sharp 90 degree angles wherever a bend is unavoidable.

4. Why does my exhaust duct need a backdraft damper?

The damper opens when the fan runs and closes when it is off, which keeps outside air, insects, and debris from entering your kitchen through the vent when the hood is not in use.

5. How often should a commercial kitchen duct be cleaned?

Cleaning frequency depends on cooking volume, but many fire codes call for cleaning every three to six months in high volume kitchens, with longer intervals for lighter use. Local fire marshals usually set the exact requirement.

6. Is it okay to vent a range hood into the attic instead of outside?

No. Venting into an attic or any enclosed space traps grease, heat, and moisture, which can lead to mold, structural damage, and fire risk. The duct always needs to terminate outside through a proper wall or roof cap.