Installed new bathroom exhaust fan in Riccarton where bathroom had terrible mold problem. Their old fan was tiny and barely worked - just moved air around without actually venting outside. We removed old fan, cut proper duct opening through ceiling and roof, installed good quality quiet fan, ran ducting to roof vent, wired fan to light switch with timer delay. Fan now runs automatically when light turns on then continues for 10 minutes after light goes off. Pulls steam out properly instead of letting it sit in bathroom. Family said within couple weeks they noticed less condensation on mirrors and walls. Mold problem cleared up after few months once bathroom stayed drier.
Proper exhaust fan wiring and ducting makes huge difference in moisture control. Just mounting fan in ceiling isnt enough - needs power supply and must actually vent outside to work properly.
Why Proper Exhaust Fans Matter
Good exhaust ventilation solves several problems.
Moisture removal prevents mold growth. Bathrooms and kitchens produce lots of steam and moisture. Without ventilation moisture condenses on walls and ceiling creating perfect mold conditions. Exhaust fan pulls moisture out before it can cause problems.
Odor removal keeps house fresh. Cooking smells and bathroom odors linger without ventilation. Exhaust fan removes odors immediately.
Air quality improves with ventilation. Kitchens produce smoke, grease particles, gas combustion products. Bathroom might have chemicals from cleaning products. Exhaust fan removes all these contaminants.
Paint and wallpaper last longer in well ventilated spaces. Moisture causes paint to peel and wallpaper to lift. Good ventilation protects these finishes.
Building code requires exhaust ventilation. Bathrooms without windows must have exhaust fans. Kitchens need ventilation over cooking surfaces. Not optional - its required.
Types of Exhaust Fans
Different fans for different purposes.
Standard bathroom fans mount in ceiling. Pull air from bathroom and exhaust outside through duct. Typical residential fan moves 50-100 cubic feet per minute. Enough for most bathrooms up to maybe 80 square feet.
High capacity bathroom fans for large bathrooms or ensuites with separate toilet. Maybe 150-200 CFM. Needed for bigger spaces or multiple rooms sharing one fan.
Combination fan lights are common. Fan and light in one unit. Saves ceiling space and installation cost. Can have separate switches or single switch.
Heat lamp fans popular in Christchurch. Fan plus heat lamp for cold mornings. Kids especially like warm bathroom in winter. Draw more power cause of heating element.
Inline fans mount in attic with duct running to bathroom. Quieter cause motor away from bathroom. More expensive and complex installation. Used where ceiling space limited or want really quiet operation.
Kitchen range hoods different from bathroom fans. Much more powerful - 300-600 CFM typical. Designed specifically for cooking ventilation. Some vent outside, some just recirculate through filters.
Ducted vs Ductless Fans
Big difference between ducted and ductless installations.
Ducted fans exhaust outside. Only way to actually remove moisture and odors from house. Duct runs from fan through ceiling and roof or wall to outside. This is proper installation and only kind that really works.
Ductless fans just recirculate air. Have filter but dont exhaust outside. Basically useless for moisture control. Might remove some odors with carbon filter but thats it. We never recommend these for bathrooms.
Some range hoods are ductless. Recirculate through grease filters and carbon filters. Better than nothing for grease but dont remove moisture or combustion products. Ducted range hood always better.
Building code requires ducted fans in most situations. Ductless fan doesnt meet code for bathroom ventilation. Only acceptable in special situations where ducting truly impossible.
Electrical Wiring Requirements
Exhaust fans need proper electrical installation.
Circuit requirements depend on fan. Basic bathroom fan draws maybe 0.5-1 amp. Can share circuit with bathroom lights. Heat lamp fans draw more - maybe 10-15 amps. Might need dedicated circuit.
Cable run from switch to fan. Usually 1.5mm cable adequate for standard fan. Larger cable for high power fans. Run through ceiling space to fan location.
Switch location matters. Usually right by bathroom door. Code requires switch outside bathroom for safety - dont want someone turning off fan while youre showering. Switch can control just fan or fan plus light together.
Timer switches very useful. Fan continues running after you leave bathroom. Removes remaining moisture. Typical timer runs 5-20 minutes after switch off. We install these on most bathroom fans now.
Humidity sensor switches automatically run fan. Sense moisture level and turn fan on when needed. Turn off when air dry. Good option if people forget to use manual switch. More expensive but very convenient.
GFCI protection sometimes required. If fan within reach of shower might need GFCI. We check code requirements for each installation.
Installation Process
Installing exhaust fan involves ceiling work, ducting, and electrical.
Planning location comes first. Center of bathroom usually or over shower. Must be able to duct to outside efficiently. Check for ceiling joists and other obstacles.
Cutting ceiling opening. Mark hole for fan housing. Use drysaw or jigsaw to cut opening. Try to center between joists if possible.
Mounting fan housing. Secure to ceiling joists with screws or brackets. Must be solid - fan vibration loosens poor mounting.
Running ductwork. Flexible duct from fan to roof or wall vent. Keep run as short and straight as possible. Minimize bends which reduce airflow.
Installing roof or wall vent. Cut opening through roof or exterior wall. Install vent cap with proper flashing and weatherproofing. Must be sealed properly or water leaks in.
Electrical connections. Run cable from switch to fan. Connect to fan terminal block. Check connections secure. Some fans have plug connections, others hardwired.
Installing fan cover and light if applicable. Snap on or screw on depending on model. Install light bulb if has light.
Testing operation. Turn on and verify good airflow. Check quiet operation. Test switch and timer if installed.
Ducting Best Practices
Proper ducting critical for fan effectiveness.
Use rigid duct where possible. Metal duct better airflow than flexible duct. Flexible duct easier to install but creates more resistance. We use rigid duct for long runs, flexible just for short connection to fan.
Minimum duct size for airflow. 4 inch duct standard for bathroom fans. Larger diameter for high CFM fans. Undersized duct restricts airflow wasting fan capacity.
Keep duct runs short. Every meter of duct reduces airflow. Every bend reduces airflow even more. Plan shortest route from fan to outside.
Slope duct to outside. Moisture condenses in duct. If duct slopes back toward fan water drips down. Slope toward outside lets water drain out.
Insulate duct in cold attics. Warm moist air in cold duct creates condensation. Insulated duct prevents condensation problems.
Seal all joints properly. Leaky duct wastes fan capacity. Use proper duct tape or mastic sealant. Not regular tape - needs to be duct specific.
Terminate duct properly outside. Roof cap or wall cap with backdraft damper. Damper prevents cold air blowing back in. Must be weatherproofed to prevent water entry.
Switch Options and Controls
Different control options for different needs.
Basic on-off switch simplest. Flip switch to run fan. Remember to turn off when done. Works fine but people often forget leaving fan running or forget to turn on.
Timer switch sets run time. Turn on and set timer for 5, 10, 15, or 20 minutes. Fan automatically shuts off. Ensures fan runs long enough without wasting power. Most popular option.
Humidity sensing switch automatic. Detects moisture and turns fan on automatically. Turns off when humidity drops. Never need to touch switch. Perfect for people who forget. More expensive but worth it.
Combination switches control fan and light separately. Two switches side by side. One for light, one for fan. Gives independent control.
Smart switches connect to home automation. Control fan from phone. Set schedules. Monitor runtime. Integrate with other smart devices. Newest option for tech enthusiasts.
Noise Considerations
Fan noise varies dramatically between models.
Sone rating measures fan noise. Lower number is quieter. 0.5 sones is whisper quiet. 1-2 sones is quiet conversation. 3-4 sones noticeable. Over 4 sones pretty loud.
Good quality fans are quieter. Cheap builder grade fans often 3-4 sones. Premium fans might be 0.5-1.5 sones. Worth paying more for quiet operation.
Installation quality affects noise. Poorly mounted fan vibrates creating extra noise. Loose duct connections whistle and rattle. We mount fans solidly and seal everything properly.
Inline fans quietest option. Motor in attic away from bathroom. Only air movement noise in bathroom. Costs more but near silent operation.
Larger slower fans quieter than small fast fans. Moving same air volume at lower speed is quieter. Another reason to size fan properly.
Sizing Exhaust Fans
Right size fan matters for effectiveness and efficiency.
Bathroom fan sizing based on room size. Rule of thumb is 1 CFM per square foot. So 60 square foot bathroom needs 60 CFM fan minimum. Building code requires minimum 50 CFM regardless of size.
Larger bathrooms need more powerful fans. 100+ square foot bathroom might need 150 CFM. Ensuite with separate toilet area might need even more.
High humidity bathrooms need extra capacity. Bathroom with spa bath or steam shower produces way more moisture. Might need double normal capacity.
Kitchen range hood sizing different. Based on cooktop BTU output. Gas cooktop needs more ventilation than electric. Typical residential range hood 300-500 CFM.
Duct length affects required capacity. Long duct run with multiple bends reduces actual airflow. Might need higher rated fan to compensate for duct losses.
Common Installation Challenges
Exhaust fan installations sometimes hit problems.
No clear duct path to outside. Maybe two story house with bathroom on lower level. Or complex roof structure blocking path. We find alternate routes or use longer duct runs.
Ceiling joists blocking fan location. Fan housing wont fit between joists. Might need offset mounting bracket or different fan model.
Flat roof with minimal slope. Hard to install roof vent properly. Might be better to vent through wall instead.
Insulation everywhere in attic. Modern houses have thick insulation. Working around insulation to run duct is slow. Need to move insulation then put it back properly.
Old houses with no existing ventilation. Adding first fan means new wiring, new ducting, cutting roof - bigger job than replacing existing fan.
Did house in Merivale where bathroom was right in middle of house with no exterior walls nearby and complex roof structure. Had to run duct about 8 meters through ceiling space dodging beams and AC ducts to reach suitable roof location. Took three times longer than typical install but fan works great.
Kitchen Range Hood Installation
Range hoods have specific requirements.
Power requirements higher than bathroom fans. Range hood might draw 3-5 amps. Typically shares circuit with kitchen outlets but check total load.
Mounting height matters. Usually 24-30 inches above cooktop. Too low hits your head, too high loses effectiveness. Follow manufacturer specs.
Ducting usually 6 inch diameter. Kitchen range hoods move more air than bathroom fans. Need larger duct for proper airflow.
Make-up air might be required. High CFM range hoods pull so much air out that house goes negative pressure. Can cause combustion appliance problems. Building code requires make-up air for hoods over 400 CFM. Special system brings outside air in to replace exhausted air.
Grease duct requirements strict. Kitchen exhaust duct must be metal not flexible. Must be cleanable. Fire safety requirements because grease buildup is fire hazard.
Maintenance Requirements
Exhaust fans need regular maintenance.
Clean fan covers regularly. Dust and dirt accumulate. Reduces airflow and looks gross. Most covers pop off for cleaning. Wipe down or wash in sink.
Clean or replace filters if applicable. Range hoods have grease filters needing regular cleaning. Some bathroom fans have filters too. Follow manufacturer cleaning schedule.
Check duct connections annually. Flexible duct can come loose over time. Verify all connections still tight and sealed.
Inspect outside vents for blockage. Bird nests, leaves, or other debris can block vent. Check backdraft damper still operates freely.
Lubricate motor if needed. Some fans have sealed bearings never needing lube. Others benefit from annual oiling. Check manufacturer specs.
Replace fan when worn out. Typical bathroom fan lasts 10-15 years. Motor bearings wear out eventually. Noisy operation or reduced airflow means time for replacement.
Building Code Requirements
Exhaust fan installations must meet building code.
Bathroom ventilation mandatory. Any bathroom without operable window must have exhaust fan. Minimum 50 CFM capacity. Must exhaust to outside not into attic.
Kitchen ventilation required. Range hood or other ventilation over cooktop. Can be ducted or recirculating depending on situation.
Electrical installation must be certified. Licensed electrician required for wiring work. Certificate of compliance issued after installation.
Ducting must terminate outside. Code prohibits exhausting into attic, crawlspace, or wall cavity. Must go completely outside with proper vent cap.
Switch location regulated. Bathroom fan switch must be outside bathroom or must have pullcord inside. Prevents electric shock hazard near water.
Cost of Exhaust Fan Installation
Installation costs vary with complexity.
Basic bathroom fan replacement runs $200-350. Remove old fan, install new fan, simple ducting if needed. Quick job under 2 hours.
New bathroom fan installation $350-600. Cut ceiling opening, install fan, run new duct to outside, install roof vent, wire to switch. More involved job.
Range hood installation $400-700. Mounting range hood, ducting to outside through wall or roof, electrical connection. Depends on duct complexity.
Complex installations cost more. Long duct runs, difficult roof access, structural modifications add $200-500 to price.
Heat lamp fans more expensive. Additional electrical load and more complex wiring. Maybe $300-450 for installation.
Fan itself costs $50-300 depending on quality and features. Basic builder grade fan $50-100. Good quality quiet fan $150-250. Premium fan with all features $250-400.
Operating cost minimal. Bathroom fan running hour per day costs maybe $5-10 per year in power. Heat lamp fan costs more - maybe $50-100 per year if used regularly.
Upgrading Existing Fans
Replacing old fan simpler than new installation.
Duct usually stays in place. New fan connects to existing duct if properly sized. Saves cutting new roof opening.
Wiring might need updating. Old fan might have inadequate wiring. Upgrade to proper size cable if needed.
Modern fans usually quieter than old ones. Technology improved significantly. Replacing 15 year old fan with new one dramatically reduces noise.
Adding timer or humidity sensor when replacing. Good time to upgrade switch. Small extra cost for big convenience improvement.