Rangehood and Exhaust Fan Installation: Getting It Right

Extraction is the least interesting part of a kitchen or bathroom, and the part people notice most when it’s wrong. Steam on the mirror, mould in the corner of the ceiling, and a house that smells like last night’s dinner at breakfast.

The good news is that getting it right isn’t complicated. It just has to be sized properly and vented somewhere sensible.

Ducted or recirculating? Duct it.

This is the decision that matters most, and it’s the one most often got wrong.

Ducted rangehoods and exhaust fans move air outside the building. The moisture, grease and odour leave.

Recirculating rangehoods pass air through a charcoal filter and blow it back into the kitchen. They catch some grease and some smell. They do nothing at all about moisture or heat, because there’s nowhere for it to go.

Recirculating exists for apartments and situations where ducting genuinely isn’t possible. If you can duct, duct. It’s a meaningfully better outcome for a modest additional cost at installation, and it’s very expensive to change your mind about later.

The same logic applies in bathrooms, with an extra warning: an exhaust fan that vents into the roof cavity is worse than no fan at all. You’re taking a bathroom’s worth of moisture and putting it into a sealed timber space. We find this constantly, and the giveaway is a stained roof cavity or mould appearing on the ceiling near the fan. It must vent through the eave or the roof, to outside.

Sizing a rangehood

Two things: width and extraction rate.

Width. The rangehood should be at least as wide as the cooktop, and ideally 100–150mm wider on each side. Steam and smoke rise in a plume that spreads — a 600mm hood over a 900mm cooktop will always be playing catch-up.

Extraction rate, measured in m³/hr. A workable rule is to size for ten to twelve air changes per hour in the kitchen volume. For a typical Melbourne kitchen of around 20m³, that’s 200–240 m³/hr as a bare minimum — and in practice, for an open-plan kitchen or serious cooking, we’d want considerably more. Gas cooktops and woks need more than induction.

Height above the cooktop. Follow the manufacturer’s specification, but generally 650–750mm above an electric or induction cooktop and a little higher over gas. Too high and it doesn’t capture; too low and it’s a fire risk and you’ll hit your head on it.

Ducting matters as much as the unit. A powerful rangehood connected to narrow, flexible, kinked ducting with four bends performs like a weak one. Use rigid ducting, the full diameter of the outlet, with as few bends as possible and the shortest practical run. This is where cheap installs cut corners, and it’s invisible once the cabinetry goes back on.

Sizing a bathroom exhaust fan

Same principle, different numbers. Aim for around 10–15 air changes per hour.

Calculate the room volume — length × width × height in metres — and multiply by 10 to 15. A 2m × 3m bathroom with a 2.4m ceiling is 14.4m³, so you want roughly 150–220 m³/hr.

Position it over or near the shower, which is where the moisture is, not by the door.

Add a run-on timer. The bulk of the moisture in a bathroom is still in the air after you’ve left. A timer that keeps the fan running 10–20 minutes after the light goes off is a small addition that makes a real difference to mould.

Zone rating matters. Fans in the shower zone need an appropriate IP rating. This isn’t optional and it’s an easy thing for a cheap install to skip.

Consider a three-in-one (fan, light, heater) in a bathroom without other heating — but be aware the heater element draws serious current and may need its own circuit, which means checking there’s room on the switchboard.

Noise

Rated in sones or dB. A fan you find unpleasant is a fan you won’t switch on, which defeats the exercise entirely.

Two things reduce noise: a larger fan running slower moves the same air more quietly than a small one working hard, and an inline fan mounted remotely in the roof cavity puts the motor noise away from the room. Inline units cost more and are noticeably quieter — worth it in a bathroom next to a bedroom.

Rangehoods are quietest at the lower speed settings, which is another argument for buying one with more capacity than you strictly need: you’ll run it on two instead of four.

Common problems we’re called to fix

Venting into the roof. Covered above. Very common, causes real damage over time.

Undersized units. Usually chosen on price or looks. A rangehood that doesn’t extract is decoration.

Flexible ducting run the long way round. Halves the effective performance.

No dedicated circuit. A rangehood or a three-in-one with a heater drawing off a lighting circuit is a nuisance-tripping problem waiting to happen.

Missing external cowl or damper. Without one you’ve got an open hole into your roof space, which lets weather and wildlife in and lets warm air out.

What’s involved in the install

For a rangehood: mounting, ducting out through the roof or wall with the correct cowl, and connecting to a suitable circuit — usually a dedicated one. If it’s replacing an existing unit in the same location, straightforward. If it’s a new location, or a change from recirculating to ducted, more involved.

For a bathroom fan: cutting in, mounting, ducting to an eave or roof vent, and wiring in with the switching and any timer. If we’re already in the ceiling we’ll often suggest sorting out the lighting at the same time.

Both are electrical work and both need a licensed electrician in Victoria.

Talk to us

We install rangehoods, exhaust fans and kitchen appliances across Melbourne’s eastern suburbs. We’ll size it properly, duct it outside, and tell you honestly when the unit you’ve picked isn’t going to do what you want it to.

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Get in touch.