When installing a bathroom fan, choosing the right type of vent is crucial for proper ventilation and moisture removal. Bathroom fans help remove humidity, odors, and other pollutants from the air, creating a healthier bathroom environment. Selecting the wrong vent can lead to mold, mildew and moisture damage over time. There are several factors to consider when deciding what type of vent to use with your bathroom fan, including climate, attic or roof type, and building codes. In this article, we will discuss the most common types of bathroom venting and provide recommendations to help you choose the best option for your home.
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Should bathroom fans vent into attic or outside?
Bathroom fans should always vent to the outdoors if possible. Venting into an attic or ceiling space allows moisture to accumulate and can lead to mold growth in these areas over time. Proper venting to the exterior will remove moisture from the home more effectively. Building codes typically require bathroom exhaust fans to be vented outside whenever feasible.
Venting a bathroom fan into the attic can be acceptable only if the attic has proper ventilation itself. Passive attic vents or gable vents can allow any residual moisture from the bathroom fan to escape the attic space. However, venting directly through the roof or wall to the outside is still the preferred method.
Some of the benefits of venting bathroom fans directly outdoors include:
– More effective moisture removal
– Reduced risk of mold and mildew growth
– Odors expelled from the home
– Compliance with most building code requirements
If venting a fan outside is not possible, installing a high-quality, ENERGY STAR rated fan with a moisture sensor and timer can help minimize moisture buildup when venting into the attic. The fan should run for 20-30 minutes after use to fully clear humidity. Proper attic ventilation is also crucial.
Through the roof vents
Venting a bathroom fan through the roof is the most direct and effective venting method. This involves running ductwork from the fan housing up through the attic and penetrating the roofline. The ductwork is covered by a weatherproof roof cap on the exterior of the home.
There are several types of roof caps that can be used:
– **Round roof caps** – These are the most common. Round caps have a hood that helps prevent backdrafts.
– **Gooseneck roof vents** – Goosenecks allow for a more vertical duct run. This can help optimize airflow when space is tight.
– **Flashing roof caps** – Flashing vents integrate with the roof shingles for a low profile. No hood is needed.
– **Roof jack covers** – Roof jack kits include a cover that fits over top of the ducting. These are easy DIY options.
Some benefits of roof vents include:
– Short, direct duct run improves airflow
– Duct run is fully concealed in attic
– Vapor barrier can be maintained
– No exterior wall penetration needed
Potential downsides include:
– Penetrating the roof requires proper sealing
– Exposure to wind and weather may reduce airflow
– More difficult to install or replace fans in the future
Overall, a through-the-roof vent is an ideal solution in most cases, provided it is properly installed and sealed. This offers the most effective ventilation.
Wall vents
Venting a bathroom fan through an exterior wall is another common option. This involves running ductwork horizontally from the fan housing until it penetrates the siding. A weatherproof cap is installed to cover the outside ventilation opening.
There are several types of wall caps that can be used:
– **Round wall caps** – Directly fitted to round ductwork. A rear damper prevents backdrafts.
– **Rectangular wall caps** – Designed for rectangular ducting. Also available with dampers.
– **Exterior wall louvers** – Blend in with siding and provide airflow. No rear damper.
– **Wall plates** – Grilles covering a wall hole. Provide minimal weather protection.
Some potential advantages of wall vents are:
– Usually easier to install than roof vents
– Accessible for inspection, cleaning and replacement
– Does not penetrate the roof
Possible disadvantages include:
– Ductwork is not concealed
– Turns and bends in ductwork can hinder airflow
– Outdoor contaminants may enter through wall penetration
Wall vents work best for shorter duct runs up to about 10-15 feet. Maintaining smooth ducting without tight turns boosts air velocity. Wall vents are a convenient option, but not as effective for moisture removal as direct roof vents.
Types of ducting
The type of ducting used when installing a bathroom vent can impact airflow performance. Here are some key types of ducting to consider:
– **Smooth metal** – This includes aluminum and galvanized steel. It offers the best airflow and is easiest to clean. Sturdy round or rectangular shapes available.
– **Flexible plastic** – Easy to install around corners, but more prone to sagging and kinks which reduce airflow. Should be kept short.
– **Flexible insulated** – Has an insulation layer to reduce condensation buildup inside the duct. Preferred for long cold-climate runs.
– **Rigid PVC** – Lightweight plastic that holds its shape well. Flow is good, but hard to cut and install. Louvered section are available.
– **Dryer vent** – Not recommended as it traps moisture and lint. Poor flow when extended. For emergency use only.
Key ducting best practices:
– Use smooth metal or rigid plastic whenever possible
– Size ducting to match fan outlet
– Limit flexible ducting to short runs under 10 feet
– Keep duct runs as straight as possible
– Slope ducts downwards 1/4″ per foot if venting through roof
Proper ducting is essential for adequate airflow. Smooth metal ducting is ideal, but flex ducting will suffice for shorter runs. Overly long or restrictive ducting can cause a fan to be noisy and ineffective.
Passive vents
Passive attic vents should be used to provide background ventilation to an attic space. However, they should not be relied upon as the primary ventilation method for a bathroom fan. Passive vents include:
– **Gable vents** – Located in the attic gable ends under the eaves. Effective for air crossover.
– **Roof vents** – Installed along the roof ridge or eaves. Mostly for hot air release.
– **Soffit vents** – Mounted under roof overhangs to connect attic to exterior. Work best with ridge vents.
While passive vents help exchange attic air, they do not offer the directed exhaust airflow needed for bath humidity control. At best they may serve as secondary attic ventilation if bathroom fans must vent into the attic. Active ventilation using properly installed ducting is still the recommended approach for bath fans.
CFM and Sones
When selecting a bathroom vent fan, the CFM rating and sones level are two key specifications to consider:
– **CFM** – This stands for cubic feet per minute. The higher the CFM, the more air a fan can move. Look for a CFM rating that matches or exceeds the bathroom’s square footage.
– **Sones** – This measures how loud the fan is during operation. Lower sones means a quieter fan. Look for 1.5 sones or less for a reasonably quiet fan.
The chart below provides some guidelines for CFM and sones based on bathroom size:
| Bathroom Size | Recommended CFM | Recommended Sones |
|---|---|---|
| Small bath under 100 sq. ft. | 50-80 CFM | 1.0 or less |
| Average bath 100-150 sq. ft. | 80-110 CFM | 1.0 – 1.5 |
| Large bath over 150 sq. ft. | 110-150 CFM | 1.5 or less |
Choosing a fan with adequate CFM will ensure it can remove moisture, odors and air pollutants. Selecting a quieter sones rating will provide pleasant, unobtrusive operation.
ENERGY STAR fans
Selecting an ENERGY STAR qualified bathroom vent fan is recommended for several reasons:
– **Higher efficiency** – ENERGY STAR models must meet minimum CFM/watt standards that translate to better airflow using less energy. This saves on utility costs.
– **Quieter operation** – They must meet sound rating requirements at various CFM levels meaning less noise.
– **Moisture-sensing** – Many are designed with humidity sensors and timers that allow intermittent, as-needed operation during and after use.
– **LED lighting** – If lighting is included, it must use efficient LED bulbs.
– **Higher quality** – Products must meet performance criteria tested by third parties. This results in more durable, long-lasting products.
While ENERGY STAR fans may have a higher upfront cost, the performance and energy savings make them worth the investment for most homeowners. Their energy-efficient operation will save money over years of use.
Smart vents
Smart vents are a newer category of bathroom fans incorporating technology for added performance and convenience:
– **Automated operation** – Occupancy sensors or humidity sensors activate the fan automatically when needed.
– **Variable speeds** – Speeds are increased as humidity levels rise to reduce noise.
– **Timed run-on** – Fans are programmed to run for a set time after use ends to fully exhaust moisture.
– **Night light/fogger** – Motion sensing lights and steam assisting features are available.
– **Mobile app control** – Fans can be operated remotely via phone apps and voice assistants.
– **Indicators** – Provide filter change, humidity level, error code and other alerts.
Smart bathroom fans provide automated, hands-free operation for improved air quality and lower humidity levels. Features like app controls and speed adjustments add high-tech convenience. Prices are coming down on smart models.
Condensation concerns
Excessive condensation around a bathroom vent is an indication of improper installation or dysfunction:
**Causes of condensation around vents:**
– Inadequate CFM for space size
– Leaks around fan housing
– Wrong exhaust location allowing air backflow
– Under-insulated or improperly sealed ductwork
– Extended runs causing moist air to cool and condense
– Outdoor humidity levels exceeding fan capacity
**Correcting excessive condensation:**
– Seal all connections with duct tape or mastic
– Insulate ducting runs, especially in cooler climates
– Slope longer duct runs down towards outlet
– Increase ventilation capacity with higher CFM
– Redirect exhaust away from eaves overhangs
– Upgrade to fan with higher cfm and moisture-sensing
– Run fan for longer periods during and after bathroom use
– Consider installing supply air ventilation.
Condensation issues indicate the need for fan improvements and properly sealing ductwork. Adjusting the vent location or upgrading the fan may be required in severe cases.
Conclusion
Choosing the proper bathroom vent configuration involves considering climate, duct run length, attic space, and building factors. Direct roof vents provide the most effective moisture removal whenever feasible. Wall vents also work well for shorter runs. Smooth metal ducting maintains maximum airflow.
Look for a quiet yet powerful ENERGY STAR fan sized for the bathroom’s square footage. Smart model bathroom fans offer automated, high-tech operation for the greatest hands-free convenience. With the right bathroom vent properly installed, humidity and condensation can be efficiently removed from the home.