Can a fart fan vent to the attic?

Whether or not a fart fan can vent into an attic space is a common question for homeowners and builders. The answer depends on several factors related to building codes, attic conditions, and the performance of the fan itself.

Building Codes

Most building codes do not allow bathroom exhaust fans to vent directly into attics for a few key reasons:

• Attic ventilation – Venting moisture into an attic can lead to problems with proper attic ventilation and moisture buildup.
• Mold and mildew – Excess moisture in attics can lead to mold, mildew, and wood rot issues.
• Insulation performance – Moisture can reduce the effectiveness of attic insulation.

Instead, building codes require bathroom exhaust fans to vent outside the home. This is usually done by running ductwork from the fan through the attic and out through the roof or gable end. The ducting helps remove moist air from the home and prevent moisture issues in the attic space.

Attic Conditions

Even if building codes would allow venting a fart fan directly into an attic, the conditions in the attic may not be suitable. Key factors to consider include:

• Attic ventilation – Does the attic have proper ridge, soffit, and gable vents to allow moisture to be removed?
• Insulation – Is insulation blocking airflow and moisture dissipation in the attic?
• Climate – Cooler, drier climates may be more forgiving than hot, humid climates.

Venting moist bathroom air directly into an attic in a hot, humid climate with poor attic ventilation would almost certainly cause moisture problems over time.

Fan Performance

Bathroom fans meant for roof venting are designed differently than inline fans meant for short indoor duct runs:

• CFM rating – Roof fans have higher airflow (CFM) ratings to overcome the resistance of long ductwork.
• Sone rating – Roof fans are designed to be quieter (lower sone ratings) so fan noise is less noticeable inside the home.
• Dampers – Roof fans have backdraft dampers to prevent air flowing back into the attic.
• Ducting – Long lengths of insulated, sloped ducting is recommended.

An inline fan would likely underperform if only venting into a short attic run. The lower airflow could lead to moisture buildup.

Alternatives to Consider

If directly venting into the attic is not permitted or ideal, what are the options?

• Roof venting – Install a powerful roof-mounted fan and properly insulated ductwork.
• Gable venting – Duct the fan out through a gable vent.
• Soffit venting – Vent through the home’s soffits or overhangs.
• Inline fan to roof jack – Use an inline fan connected via a roof jack.
• Condensation fan – Use a condensation type fan that reduces moisture without venting out.

Roof venting is the most thorough solution. But the other options can also work if designed and sized properly. In a pinch, even venting into a well-ventilated attic crawl space could work, but consult local codes first.

Conclusion

In summary, building codes prohibit venting bathroom exhaust fans directly into attics due to concerns over proper attic ventilation, moisture accumulation, mold growth, and insulation performance. Even if allowed by code, typical attic conditions and standard inline fan performance usually make direct attic venting inadvisable. The best practice is to vent bathroom fans to the building exterior via roof or wall termination. For attic installation, the use of roof-mounted fans and properly installed insulated ductwork is recommended.

Factors to Consider When Venting a Bathroom Fan into an Attic

While venting a bathroom fan directly into an attic is not usually recommended, there are some factors to consider if this will be attempted:

Ventilation

• Is there proper ridge venting and soffit venting to allow airflow through the attic?
• Can additional gable end vents or roof vents be added to improve airflow?
• Is insulation blocking ventilation pathways in the attic? Can baffles be added?

Climate Conditions

• What is the typical relative humidity in the area? High humidity climates increase concerns.
• How extreme is the temperature range? High attic temperatures increase ventilation needs.

Fan CFM Rating

• Is the bathroom fan CFM rating high enough for just an attic duct run? Most building codes require 50-80 CFM.
• Can a higher CFM fan be installed to improve airflow and moisture removal?

Attic Volume

• Is the attic space large enough to dissipate moisture? Small attics are higher risk.
• Does the attic space cover just the bathroom or multiple areas? The more area the better.

Ducting

• Can the fan ducting be lined with insulation to reduce condensation?
• Is ducting sloped down and away from the fan to improve drainage?

Improving these factors can help mitigate risks, but directly venting to the exterior is still the recommended approach in most cases.

Building Code Requirements for Bathroom Fan Venting

Most building codes have specific requirements for bathroom exhaust fans to avoid venting directly into attics. Common code requirements include:

Code	Requirement
Vent Termination	Fans must terminate outside the building, not into attics or interstitial spaces.
Ducting	Ducts must have smooth interior surfaces, be air tight, and insulated in attics.
Minimum CFM	Fans must provide adequate airflow, typically 50-80 CFM depending on room size.
Sone Rating	Maximum sound rating of 1.5-3 sones, depending on fan location.
Clothes Dryer Venting	Clothes dryers cannot share the bathroom fan ducting.

Building codes aim to reduce moisture issues in attics and prevent problems like mold growth or wood rot. Homeowners should consult local building codes when installing bathroom ventilation.

Health Risks of Venting Bathroom Fans into Attics

Venting bathroom exhaust fans into attics can potentially lead to some health hazards if moisture issues occur:

Mold Growth

• Moisture buildup can lead to mold growth in attics.
• Some types of mold release spores that can be inhaled and cause health issues.
• Allergies, asthma, and respiratory issues are concerns with mold exposure.

Wood Rot and Wall Damage

• Trapped moisture can rot and weaken attic wood, roof sheathing, and wall materials.
• Eventually, excess attic moisture can penetrate into living areas leading to interior wall mold.

Pests

• Moist attics can attract pests like insects, bats, squirrels, and rodents.
• Some pests can spread diseases or trigger allergies and asthma.

Reduced Air Quality

• Excess humidity reduces indoor air quality and makes environments feel stale.
• Poor indoor air quality can worsen respiratory problems like allergies and asthma.

Following proper bathroom fan venting procedures helps keep attics dry and prevents associated health hazards.

Tips for Installing Bathroom Fans to Minimize Attic Moisture

When installing a bathroom exhaust fan, there are some tips to follow to minimize attic moisture:

• Vent exhaust outside whenever possible, not into the attic.
• Select a powerful, quiet fan – typically 70-80 CFM and ≤ 1.5 sones.
• Use insulated rigid ductwork rated for bathroom exhaust.
• Slope ducts downward to allow condensation to drain.
• Install a backdraft damper at the roof termination.
• Seal all duct connections with aluminum tape or mastic.
• Install a timer switch to run the fan for 20+ mins after showering.
• Consider wiring the fan to a humidity sensor controller.

Following best practices for installing bathroom ventilation can dramatically reduce problems with attic moisture, mold growth, pests, and indoor air quality.

Solutions for Removing Moisture from an Attic after Venting a Fan

If a bathroom fan was vented into an attic causing moisture issues, there are solutions for removing that moisture:

Improve Attic Ventilation

• Add more soffit, ridge, and gable end vents to increase passive airflow.
• Install a powered attic ventilation fan to actively push out moist air.
• Ensure insulation baffles are keeping vents open and clear.

Use Dehumidifiers

• Use heavy-duty dehumidifiers designed to operate in high temperatures.
• Automatically drain the dehumidifiers outside rather than emptying buckets.
• Seal attic hatches/doors to contain moisture to the attic space.

Vent the Fan Outside

• Reroute the bathroom fan ducting from the attic to vent outside.
• Replace inline fans with a roof-mounted fan and insulated ductwork.

Replace Insulation

• Remove and replace any moisture-damaged or moldy insulation.
• Seal gaps where moisture could enter from the attic into wall voids.

Acting quickly to remedy excessive attic moisture can often prevent lasting damage. But the ultimate solution is venting bathroom fans to the outdoors.

Alternatives to Venting Bathroom Fans into the Attic

For homeowners seeking bathroom ventilation without attic venting, there are several options:

Roof Venting

• Roof vents provide the best moisture removal.
• Roof fans with insulated ductwork are recommended.
• May require penetrating the roof or a dormer/chimney chase.

Wall Venting

• Vent through a gable end wall or exterior soffit overhang.
• Short duct runs often work with many inline fans.
• Watch noise levels as exterior vents are harder to muffle.

Recirculating Fans

• Use a fan with a charcoal filter to recirculate indoor air.
• Good option when exterior venting isn’t possible.
• Removes odors but less effective at moisture removal.

Dehumidistat Fan

• Fan cycles on/off based on a humidity sensor reading.
• Removes moisture without running continually.
• Can be installed with or without exterior venting.

With careful planning, there are good alternatives to venting into attics in most situations.

Conclusion

Venting bathroom exhaust fans directly into attics is never advisable. Building codes prohibit this practice as it can lead to excessive attic humidity, mold growth, pest infestations, insulation issues, and other moisture related problems. There are significant health hazards associated with improper ventilation. The proper technique is to route ducting from bathroom fans to the building exterior. Roof venting with an insulated ductwork is ideal. Wall venting or recirculating fans are also options. With careful planning and proper installation, there are solutions available to avoid the risks of venting bathroom fans into attics.