A range hood does two things essential for kitchen function: removes cooking grease and smoke from the air, and exhausts steam and combustion byproducts to the outside. Vented hoods (ducted to outside) are the standard; recirculating hoods (filter air and return to kitchen) are inferior alternatives where ducting isn't possible. The Ontario Building Code requires range hoods on gas cooktops to vent to outside.

This guide covers a standard under-cabinet range hood install with vented exhaust. Wall-mount chimney hoods, island hoods, and downdraft systems use similar principles with different mounting.

Before you start

Three things to settle:

1. CFM rating to range size. Standard rule: 100 CFM per linear foot of range. A 30-inch range (2.5 ft) needs 250 CFM minimum; a 36-inch (3 ft) needs 300 CFM. Higher-output ranges (gas vs electric) need higher CFM. Undersized hoods can't keep up; oversized hoods waste energy.

2. Duct path to outside. Vented hoods must terminate outside (not in attic, not in soffit cavity). Plan the duct path during install: through the cabinet bumper above hood → through wall or roof → outside cap. Standard duct sizes: 6 inches for 200-400 CFM; 7-8 inches for higher CFM.

3. Make-up air requirements. Modern hoods over 400 CFM may require dedicated make-up air per Ontario code — without it, the powerful hood depressurizes the home, sucking dangerous gases (carbon monoxide) from gas appliances back into the home. Verify code requirements for your specific hood and home.

What you'll need

Tools

Drill with bits
Hole saw (matched to duct size, typically 6 inch)
Reciprocating saw or jigsaw (for cutting into wall/ceiling)
Voltage tester
Phillips screwdriver
Stud finder
Tape measure and level
Wire strippers
Caulking gun

Materials

Range hood (matching size to range, CFM to needs)
Duct (rigid metal preferred over flexible; 6-8 inch matching hood)
Wall or roof cap (with backdraft damper) for exterior termination
Foil tape (NOT standard duct tape) for sealing duct joints
Wire connectors
Mounting screws (typically included)
Cable clamp (for electrical entry into hood)

Vented to outside, not into the attic

Recirculating hoods (filter and return air to kitchen) are inferior. Vented hoods (duct to outside) are the standard for any meaningful cooking.

Ducting must terminate outside the building envelope — through a wall cap or roof cap. Venting into the attic dumps grease-laden moisture into the attic, causing mold and ice dams. It's also a code violation.

Step-by-step instructions

Remove existing hood (if replacing)

Turn off the breaker. Verify with voltage tester.

Disconnect electrical wires. Disconnect duct connection.

Unscrew mount fasteners. Lower the existing hood out of the cabinet.

Verify duct path and rough out hole if new

If replacing: existing duct hole should align with new hood. Verify dimensions match.

If new install: cut hole through cabinet bumper above the hood, then through the wall/ceiling along the duct path, finally through the outside wall or roof for the termination cap.

Use hole saw matched to duct size. Make holes slightly larger than duct for easier routing.

Install the duct termination cap

From outside, install the wall cap or roof cap. Apply exterior caulking around the cap to prevent water intrusion.

The cap has a backdraft damper that prevents cold air from blowing back through the duct.

Run the duct from termination back to the hood location

Connect duct sections from the exterior cap, through the building, to the hood location. Use rigid metal duct where possible — flexible duct restricts airflow.

Seal every joint with aluminum foil tape (rated for HVAC). Do NOT use standard duct tape — it dries out and fails.

Verify the duct path is as straight as possible. Each elbow reduces airflow by ~10%.

Wire the hood (with power off)

At the hood location, the wiring connects to a junction box on the back or top of the hood. Connect:

Black to black (hot), white to white (neutral), green/bare to ground.

Use wire connectors. Pull-test.

Lift the hood into position

With a helper, lift the hood up to the underside of the cabinet. Align with mounting holes (in the cabinet bumper above) and the duct connection.

The hood's duct flange should fit into the duct connection. Wiring should connect to the existing electrical.

Secure the hood with mounting screws

Drive the included mounting screws through the hood's mounting holes into the cabinet bumper. Typically 4-6 screws.

Tighten until the hood sits firmly against the cabinet underside.

Seal the duct connection

At the joint between the hood's duct flange and the duct, wrap with aluminum foil tape. Verify no air can escape around this joint.

Air leaks here reduce the hood's effective CFM and let grease coat the cabinet bumper above.

Restore power and test

Switch the breaker on. Test the hood — fan should start, lights should work.

With the hood running, hold a tissue near the air intake. The tissue should be sucked toward the hood.

Outside at the cap, the backdraft damper should be open and air flowing out.

Common mistakes that cost you

Recirculating instead of venting. Recirculating hoods just filter; they don't remove moisture and combustion byproducts. Always vent outside if possible.
Standard duct tape on duct joints. Dries out and fails within 2 years. Always use aluminum foil tape rated for HVAC.
Undersized CFM rating. 100 CFM per linear foot of range minimum. Undersized doesn't keep up with cooking output.
Restrictive duct path. Multiple elbows and long runs reduce airflow significantly. Plan duct path to minimize bends.
Skipping make-up air on high-CFM hoods. Hoods over 400 CFM can depressurize home and pull combustion gases back. Verify code requirements.

Frequently asked questions

How much CFM do I need?

Standard: 100 CFM per linear foot of range. A 30-inch range needs 250 CFM minimum; a 36-inch needs 300 CFM.

Higher-output ranges (especially gas) benefit from higher CFM. Lower-output (electric coil) work fine at minimum spec.

Can I install a recirculating hood instead?

Recirculating hoods filter and return air to the kitchen. They're inferior to vented hoods because they don't remove moisture or combustion byproducts.

For gas cooktops, code requires venting to outside. For electric, recirculating is allowed but vented is strongly preferred.

Do I need make-up air?

Hoods over 400 CFM may require dedicated make-up air per Ontario code. Without it, the hood depressurizes the home and can pull dangerous gases (CO from gas appliances) back into the home.

Verify code with local building inspector for your specific hood capacity.

When to call us instead

If you're installing a high-CFM commercial-grade hood, a chimney hood with custom ducting, or replacing in a kitchen with old wiring or no existing duct, this becomes a significant project. We do range hood installation as part of kitchen renovations.

Book a free 60-minute site visit →

Related Ottawa services

If you're updating kitchen ventilation and appliances, our kitchen renovation team handles ducting, electrical, and appliance installation as fixed-price scopes. Book a free 60-minute consultation.