Having proper ventilation is crucial in bathrooms to remove moisture, odors, and pollutants. While one exhaust fan is usually sufficient for a standard bathroom, sometimes two exhaust fans are needed to meet ventilation requirements. The quick answer is yes, you can have two exhaust fans in one bathroom, provided some key factors are considered.
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Why Would You Need Two Exhaust Fans?
There are a few main reasons why you might need or want two exhaust fans in a bathroom:
- The bathroom is large and one fan cannot adequately ventilate the entire space.
- The bathroom has two separate areas like a water closet and shower that require dedicated venting.
- Improved moisture and humidity control is needed in a humid climate.
- Faster air exchange is desired after showering.
- There is an exterior venting issue and two fans are an alternative solution.
For large, open bathrooms one exhaust fan may not be able to effectively ventilate the entire space. The fan capacity in cubic feet per minute (CFM) needed is based on the square footage of the bathroom. A bathroom over 100 sq ft may require two fans to meet the ventilation CFM requirements.
Bathrooms with distinct zones like a water closet and shower room may benefit from dedicated exhaust fans in each space. This allows focused venting where the moisture and odors originate.
In hot and humid climates, reducing moisture and humidity are especially important. Dual exhaust fans can help keep bathrooms dry and prevent mold growth. This also helps remove odors from the air more effectively.
For bathrooms frequented by multiple people, like in a family home, a dual exhaust fan setup can help clear moist air and odors more quickly after showering.
Sometimes an exterior venting issue makes installing one powerful exhaust fan unfeasible. Using two lower CFM fans and ducting them to separate soffit vents is an alternative.
Sizing Guidelines
When installing two exhaust fans, follow these general sizing guidelines:
- Choose ENERGY STAR rated fans to get good performance while saving energy.
- Select fans that meet or exceed the recommended CFM for the bathroom’s square footage.
- The combined CFM of the two fans should meet the bathroom’s ventilation needs.
- Size the fans to run at 0.1 CFM per square foot of bathroom space.
- For humid climates, size up to 0.5 CFM per square foot.
Many bathroom exhaust fans range from 50-110 CFM for residential use. Combining two 90 CFM fans would provide 180 CFM – adequate for bathrooms up to 180 square feet. Choose quieter fans rated for continuous use to allow ventilation to run during and after bathing without annoyance.
Exhaust Fan Placement
Optimizing where the two exhaust fans are installed improves their ventilating effectiveness:
- Position each fan on opposite ends of the bathroom space.
- Place fans high on walls or ceilings to pull moisture upwards.
- Locate fans near and over key moisture sources like tubs and showers.
- Avoid installing both fans on the same wall.
- Allow for duct runs to exterior vents in optimal locations.
Installing the exhaust fans on opposite walls creates cross-ventilation which improves air circulation. Mounting the fans high on walls or ideally on the ceiling also encourages upward moisture movement.
Positioning fans close to and above high humidity sources like showers enables them to capture and remove that moist air most effectively. Avoid locating both fans on the same wall if possible.
Take into account duct run requirements when determining fan locations. Try to limit lengths and turns for optimal air flow.
Ducting Considerations
Properly ducting the two exhaust fans to the exterior is key for proper moisture removal:
- Use rigid, smooth metal ductwork to maximize air flow.
- Each fan should have its own dedicated ductwork.
- Minimize duct run length and elbows as much as possible.
- Use short, straight duct runs with minimal bends.
- Vent each fan duct independently through roof or soffit.
- Seal duct connections thoroughly with aluminum tape.
Rigid metal ductwork works best for bathroom exhaust fans versus flexible plastic ducts. Less airflow resistance allows the fans to ventilate as intended. Each fan should have its own ductwork running to a separate exterior vent. This allows both fans to function optimally.
Limiting duct length and turns is also important to maximize air flow. Duct runs over 15 feet or with multiple sharp elbows can decrease exhaust fan performance. Take routes to the exterior that are as short and straight as possible. Seal all duct connections thoroughly with metal tape to prevent leakage.
Electrical Wiring
The electrical wiring needs consideration when installing dual exhaust fans:
- Fans should be on separate circuits with dedicated switches.
- Use at least 14/2 gauge wire for each exhaust fan.
- Follow all local electrical codes and regulations.
- Consider wiring both fans to a single 20 amp circuit.
- Use a dual function switch for independent fan control.
Running the two exhaust fans on separate electrical circuits with dedicated switches allows each fan to be controlled independently. 14/2 gauge wire is typically recommended for bathroom ventilation fans. Follow all local building codes and regulations when wiring the fans and switches.
As an alternative, the fans can be wired to a single 20 amp circuit if the combined load is less than 20 amps. Install a dual function switch to allow turning on each fan separately while on the same circuit.
Controlling Humidity
Strategies for controlling humidity with dual exhaust fans include:
- Run both fans during and for at least 20 minutes after showering.
- Use a timer switch to run fans for a set duration.
- Install a humidity sensor switch to automatically control the fans.
- Let the fans run continuously at low speed during humid conditions.
- Turn on the fans manually when additional ventilation is needed.
Use the dual exhaust fans to maximize moisture removal while showering and for a period after. A timer switch can allow setting the fans to run for a set time, like 30 minutes. An electronic humidity sensor allows automatically turning the fans on when the relative humidity rises to a certain point, usually around 50-60%.
In humid climates, run the fans continuously at low speed to keep the air drier. Turning the fans on manually when needed is also an option for controlling humidity levels in the bathroom.
Cost Considerations
The main costs of installing two exhaust fans in a bathroom include:
- Purchase price of the exhaust fans – $50 – $250 each.
- Vent hoods, ductwork, and roof/soffit vents – $100 – $300 total.
- Wiring and electrical work if needed – $100 – $250.
- Labor for installation work – $200 – $500.
Higher CFM, more features, and better quality increase the exhaust fan cost. Venting materials, extensive ductwork, electrical work, and professional installation add more to the total project budget. Luxury bathrooms with twin exhaust fans can cost over $2,000 installed. However, a basic dual exhaust fan setup suitable for most bathrooms can be implemented for under $500 – $800 in many cases.
Maintenance
Regular maintenance helps dual exhaust fans work properly and last longer:
- Clean fan covers and grilles regularly.
- Dust or vacuum fan blades and housings once a year.
- Confirm vent hoods are not obstructed outside.
- Check wiring connections are tight.
- Replace filters if applicable.
- Re-seal any leaking ductwork connections.
Wipe exhaust fan covers and grilles periodically to keep dust buildup minimal. The fan blades and housings should be cleaned annually to remove dirt and debris accumulation. Make sure vent hood openings outside stay clear of obstructions like plants or debris. Check that wiring connections are still tight on both fans. Replace any filters in duct fan housings per the manufacturer’s recommendations. Use aluminum tape to re-seal any leaking or disconnected duct joints.
Key Takeaways
- Two bath exhaust fans help ventilate large bathrooms, separate zones, and improve humidity control.
- Select ENERGY STAR models sized for the bathroom’s CFM needs.
- Proper placement over moisture sources improves ventilation efficiency.
- Dedicated, short duct runs for each fan keep airflow optimal.
- Fans should be on separate circuits with individual switches.
- Humidity can be managed by running fans at key times and using controls.
- Regular maintenance keeps dual exhaust fans working properly.
Conclusion
Having two exhaust fans can greatly improve ventilation and humidity control in bathrooms, especially larger spaces. When properly sized and installed, dual exhaust fans are an effective solution for removing moisture, controlling odors, and clearing the air after showering. Following key guidelines for fan selection, placement, ducting, and wiring creates an optimal dual exhaust setup. With periodic maintenance, two exhaust fans can provide superior bathroom ventilation for many years.