Extractor Fan Airflow Calculator
Calculate Your Bathroom's Ventilation Needs
The right extractor fan prevents mold growth and maintains healthy air quality. This tool calculates the minimum airflow required based on room dimensions.
Enter room dimensions to calculate your minimum airflow requirement (m³/h)
Based on New Zealand Building Code Clause G12 requirements, your bathroom needs at least 10 air changes per hour.
Remember: Improperly sized fans cause mold growth (60% of failures within 3 years). Professional sizing is critical for health and safety.
If your extractor fan is making a noise like a dying dragon, or it’s not pulling out steam at all, you’re not just dealing with an annoying appliance-you’re risking mold, mildew, and poor air quality. Replacing it isn’t just about swapping out a broken part. You need someone who knows how to handle ductwork, electrical safety, and building codes. So who actually replaces an extractor fan? It’s not your handy neighbor with a screwdriver and a YouTube tutorial.
Electricians Are the Most Common Choice
Most extractor fans run on household electricity, and they’re wired directly into your home’s circuit. That means any replacement job requires someone licensed to handle live wires. In New Zealand, only registered electricians can legally connect or modify fixed wiring. Even if you buy the new fan yourself, you still need a qualified electrician to install it safely.
Electricians don’t just hook up power. They check if your existing circuit can handle the load, test for grounding issues, and make sure the fan is on a dedicated circuit if required by the Electrical (Safety) Regulations 2010. Many older homes have outdated wiring that can’t support modern, high-efficiency fans. A good electrician will spot that before you pay for a new unit.
Plumbers Can Sometimes Do It Too
Wait-plumbers? Yes, especially if your extractor fan is part of a larger ventilation system connected to bathroom or kitchen plumbing. In homes with complex ducting that runs through walls or ceilings near pipes, plumbers with experience in ventilation systems often handle the replacement. They’re used to working around moisture, condensation, and waterproofing.
Plumbers are especially helpful if your fan vents directly into a roof cavity or through an external wall where flashing or sealing is needed. A bad seal here means water gets in during rain, and that leads to rot, insulation damage, and expensive repairs down the line. A plumber knows how to flash a roof penetration properly. An electrician might not.
Specialist Ventilation Technicians Are the Best Option
If you want the job done right the first time, hire a ventilation technician. These specialists focus only on extractor fans, range hoods, and whole-house ventilation systems. They don’t just install-they diagnose airflow problems, measure cubic meters per second, and recommend the right fan size for your room.
For example, a bathroom that’s 4m x 3m x 2.4m needs at least 180 m³/h of extraction. A ventilation tech will calculate that, not guess. They also know which fans meet the Building Code Clause G12 for moisture control. Most DIY fans sold at hardware stores don’t. You could end up with a fan that’s too weak, too loud, or both.
These technicians often work with builders and renovators. If you’re doing a bathroom remodel, they’ll coordinate with your carpenter and tiler to ensure the duct runs cleanly and the fan is placed where it’ll actually work.
Why Not a General Handyman?
Handymen are great for hanging shelves, fixing leaky taps, or replacing light switches. But replacing an extractor fan? That’s risky. Most handymen aren’t licensed electricians. If they wire it wrong, you could face:
- Electrical fires from overloaded circuits
- Insurance claims denied after a fire
- Fines from local councils for unapproved electrical work
Even if they claim they’ve done it before, they can’t legally sign off on the work. In New Zealand, electrical work must be certified by a licensed professional. Without that certificate, you can’t sell your house. Buyers’ lawyers will check for it.
Some handymen team up with electricians. That’s fine-but make sure you get the paperwork. Ask: “Will you provide a Certificate of Compliance?” If they hesitate, walk away.
What About the Manufacturer’s Installer?
Big brands like Extract, Broan, or Vent-Axia often list certified installers on their websites. These are usually electricians or ventilation specialists who’ve been trained on their products. They know the exact mounting brackets, duct adapters, and noise dampening techniques for each model.
Using their installer means you get full warranty coverage. If you buy a fan online and install it yourself-or hire someone unqualified-the warranty is void. That’s a $500 fan you just turned into scrap.
Check the manufacturer’s website for “Authorized Installers” near Wellington. It’s worth the extra $50-$100 to keep your warranty intact.
What to Look for Before Hiring Anyone
Not everyone who says they do extractor fan replacement is qualified. Here’s how to spot the real pros:
- Ask for their Electrical Registration Number-you can verify it on the Electricians Registration Board website.
- Check if they provide a Certificate of Compliance-this is mandatory for all fixed wiring changes.
- Ask about experience with your fan type-is it a ceiling-mounted bathroom fan? A ducted kitchen hood? Make sure they’ve installed the same kind before.
- Get a written quote-it should include removal of the old unit, disposal, new fan cost, labor, and any extra materials like ducting or insulation.
- Look for reviews mentioning ventilation-not just “fixed my sink.”
A good installer will explain why they’re choosing a particular fan model. They’ll mention airflow ratings, noise levels in sones, and whether the fan has a timer or humidity sensor. If they just say, “This one’s good,” they’re guessing.
Common Mistakes People Make
Even when you hire someone, mistakes happen. Here are the top three:
- Using flexible ducting too long-it kinks, traps moisture, and reduces airflow by up to 50%. Rigid metal ducting is better.
- Not sealing duct joints-air leaks mean your fan works harder, uses more power, and pulls in dust from the attic.
- Installing the fan too far from the source-a fan mounted far from the shower won’t pull steam effectively. It needs to be within 1.5 meters of the wet area.
These aren’t minor issues. They’re why 60% of extractor fans fail within three years-not because they break, but because they were installed wrong.
What Happens If You Don’t Replace It?
Ignoring a broken extractor fan isn’t just inconvenient. It’s dangerous. In Wellington’s damp climate, moisture builds up fast. Without proper ventilation:
- Mold grows on bathroom tiles within weeks
- Wooden window frames swell and rot
- Insulation becomes damp and loses its R-value
- Indoor air quality drops, triggering allergies and asthma
Studies by the Ministry of Health show homes without working extractor fans have 3x higher mold counts than those with properly installed units. That’s not just a cleaning problem-it’s a health risk.
And if you ever sell your house? A building inspector will check your ventilation. If the fan’s missing or broken, you’ll be asked to fix it before closing-often at a higher cost than if you’d replaced it earlier.
Final Advice: Don’t Delay
Extractor fans are one of the most ignored appliances in the home. But when they fail, the damage isn’t just on the ceiling-it’s in your health, your walls, and your wallet. Don’t wait until you see black spots on the grout. Don’t try to fix it yourself with duct tape and hope.
Call a licensed electrician or a certified ventilation technician. Get a quote. Ask for proof of registration. Make sure they’ll provide a Certificate of Compliance. And choose a fan that’s right for your space-not the cheapest one on sale.
It’s not a luxury. It’s basic home safety.
Can I replace my extractor fan myself?
You can physically remove the old fan and install the new one, but you can’t legally connect it to your home’s wiring unless you’re a licensed electrician. In New Zealand, any fixed electrical work requires certification. Doing it yourself means no Certificate of Compliance, which can void your home insurance and block a house sale.
How much does it cost to replace an extractor fan?
The total cost ranges from $250 to $700, depending on the fan model and complexity. A basic bathroom fan with simple wiring might cost $250-$350. A ducted kitchen hood with new metal ducting and a wall penetration could run $500-$700. Labor usually makes up $150-$300 of that. Always get a written quote that breaks down parts and labor.
How long does an extractor fan replacement take?
Most replacements take 2 to 4 hours. Simple bathroom fan swaps take about 2 hours. If new ducting is needed, or if the old unit is stuck behind tiles or insulation, it could take half a day. A good technician will give you a time estimate before starting.
Do I need a permit to replace an extractor fan?
You don’t need a building permit for a like-for-like replacement. But you do need a Certificate of Compliance from a licensed electrician if the wiring is changed. If you’re moving the fan location, enlarging the duct, or adding a new vent through an external wall, you may need council approval. Always check with your local council if you’re unsure.
What’s the best extractor fan for a bathroom in Wellington?
Look for a fan with at least 180 m³/h airflow, a humidity sensor, and a timer. Brands like Extract, Vent-Axia, and Broan have models designed for humid climates. Avoid cheap fans under $100-they’re loud, underpowered, and won’t last. A good fan costs $150-$250 and runs quietly on low speed most of the time, only kicking into high when needed.
