Bathroom exhaust fans serve an important purpose – they remove moisture, odors, and pollutants from bathrooms. But where should they vent these things to? Through the roof, or elsewhere? There are pros and cons to venting bathroom fans through the roof versus other locations. In this article, we’ll explore the options and help you decide what’s best for your home.
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What does a bathroom exhaust fan do?
A bathroom exhaust fan, also known as a bath fan or bathroom vent fan, is a mechanical fan designed to remove air from your bathroom to the outside of your home. Here are some of the main things it does:
- Removes humidity and moisture – Bathrooms generate a lot of humidity from hot showers and steam. If left to linger, this excess moisture can lead to mold and mildew growth.
- Eliminates odors – Bathroom exhaust fans remove unpleasant odors from toilets, dirty laundry, etc.
- Vents air pollutants – Things like chemical fumes from cleaning products are vented outside instead of spreading through your home’s air.
- Improves indoor air quality – By regularly exchanging indoor bathroom air with fresh outdoor air, it improves overall IAQ.
- Helps prevent condensation – Moisture condensing on cool bathroom surfaces can drip and cause water damage.
- Adds ventilation – Most bathrooms don’t have windows, so fans provide needed air circulation.
Basically, bath fans create a negative pressure to pull moist, smelly air out of the bathroom and replace it with clean, dry air from the rest of your home and outside. This keeps bathrooms comfortable and helps prevent mold, mildew and structural damage.
Should they vent through the roof or wall?
When installing a new bathroom vent fan or replacing an existing one, one of the big decisions is where to vent it. The two main options are:
- Through the roof – Ductwork runs vertically from the fan through the attic and out the roof.
- Through the wall – Ductwork runs horizontally from the fan directly through the exterior wall.
Venting through the roof is generally considered the preferred method by contractors and building codes. But venting through the wall is also acceptable in many cases. Let’s compare the pros and cons of each approach.
Venting through the roof:
Pros:
- Shorter duct run – For most bathrooms, the distance from the fan to the roof is shorter than running ductwork to an exterior wall. This improves airflow and performance.
- Uses straight ductwork – Vertical ducts are less likely to accumulate moisture and clog than horizontal ducts with bends.
- Less condensation – Moist exhaust has less chance to condense before exiting outdoors; condensation can damage ducts.
- Easier to pitch – Ductwork can be sloped to allow condensate to drain back; harder to pitch horizontal ducts.
- Less noise outside – Exhaust is less noticeable since it’s high up on the roof, not closer to ground level.
Cons:
- Harder installation – Getting ductwork up through the attic and roof is more labor-intensive than going through a wall.
- Roof penetration – Cutting through the roof sheathing introduces an opportunity for leaks.
- Higher cost – Extra materials, labor, and roof flashing raise the installation price over wall venting.
Venting through the wall:
Pros:
- More direct route – Ductwork runs straight through the wall, often taking the shortest path outside.
- Easier installation – Going through the wall avoids navigating ductwork through attics/soffits and roof venting.
- Lower cost – Less ducting, roof work and labor results in cheaper installation costs.
Cons:
- Increased duct maintenance – Bends and horizontal runs increase chances of moisture buildup and clogging.
- Higher condensation risk – Longer horizontal ducts allow more moist air to condense inside.
- Hard to pitch – Pitching horizontal ducts to drain condensate is more difficult.
- More exterior noise – Exhaust is released closer to ground level where it’s more noticeable.
- Aesthetics – Wall vents are visible on the exterior of your home.
As you can see, both options have their merits. The “best” venting approach depends on your specific bathroom layout, home construction, budget and personal preferences.
Key installation considerations
Here are some other important considerations when installing bath fan ducting:
- Use rigid or flexible metal ducting – Vinyl, plastic or “flex duct” have more airflow resistance and trap moisture.
- Insulate ductwork – Insulation reduces condensation buildup and prevents exhaust air from freezing in ducts.
- Make as straight a run as possible – Minimize turns and bends which can trap humidity and clog with lint/dust.
- Seal all connections – Use duct tape, mastic or caulk to seal duct joints so exhaust can’t leak into walls/attic.
- Install a backdraft damper – Dampers prevent outside air from entering when the fan is off.
- Pitch ducts downward – Pitching the duct helps drain any collected moisture back into the fan.
Proper ducting improves ventilation and reduces the chance of moisture issues down the road. Consult local building codes for any additional ducting requirements in your area.
Cost comparison
Here is a general cost comparison of venting a bathroom fan through the roof vs. through the wall:
Roof venting
- Fan unit – $80 to $250
- Metal ductwork – $1 to $2 per linear foot (often around 15-30 ft. total)
- Roof flashing & caps – $20 to $60
- Labor – $200 to $500
- Total installed cost – $400 to $1000
Wall venting
- Fan unit – $80 to $250
- Metal ductwork – $1 to $2 per linear foot (often 5-15 ft. total)
- Exterior vent cover – $10 to $30
- Labor – $100 to $300
- Total installed cost – $200 to $600
As you can see, the shorter duct run and simpler roof work generally makes venting through the wall a cheaper DIY or contractor job. But this needs to be weighed against potential added maintenance.
Main factors in deciding vent route
Here are some of the key factors to help decide the best venting approach for your specific bathroom:
- Bathroom location in home
- Attic accessibility and pitch
- Roof type and overhang
- Wall space and exterior finishes
- Existing ductwork runs
- Local venting codes
- DIY skills vs. hiring a contractor
- Budget and overall cost
Carefully consider all these factors before deciding on roof or wall venting. In some cases, one option may clearly stand out as better. Other times, you may need to weigh the pros and cons of each.
Conclusion
While venting bathroom exhaust fans through the roof is often preferred, venting through an exterior wall is also acceptable in many cases. The right choice depends on your home’s layout, system capacities, exterior finishes, installation costs and other factors. With good ducting practices, either roof or wall venting can safely remove moisture, odors and pollutants from bathrooms. Consult with HVAC and roofing pros to determine the best fan setup for your unique needs and home construction.