02/22/2026
Neither! They are both not without flaws. "A" releases moisture under the soffit and into the roof attic. "B" allows, cold or hot air in, rain and condensation to flow into the interior envelope.
The best design is horizontal through the gable with the pitch outward and exhaust air and water away from the roof line.
If you must go through the roof, use PVC pipe and use a 180° bend with the opening pointed down at least 18" above the roof material.
If you must go through the soffit, extend the piping past the roof line and gutters and point the opening down.
Bathroom Ventilation Done Right: Type A vs. Type B 🏠💧
1️⃣ Why bathroom moisture is a real issue
A hot shower can fill the room with steam in minutes. That moisture sticks to cold surfaces, turns into condensation, and slowly feeds mold. Many people only notice the problem when paint peels or the ceiling starts to smell musty.
2️⃣ What the fan is actually supposed to do
A bathroom fan isn’t just noise on the ceiling. Its job is to pull humid air out and send it completely outside. If that moisture stays in the attic or duct, it can cause hidden damage over time.
3️⃣ Type A: Venting to the soffit
This setup sends the air toward the soffit area under the roof edge. It can work, but if the duct is long, poorly angled, or exposed to cold air, condensation may build up. Sometimes the humid air even gets pushed back into the attic.
4️⃣ Type B: Venting through the roof
Here, the duct runs upward and exits through a roof cap. Moist air goes straight outside, with less chance of backflow or trapped condensation. In many homes, this ends up being the more reliable option.
5️⃣ The tiny mistakes that cause big trouble
Long, twisted ducts, no insulation, weak fans, or vents ending in the attic are common issues. Everything may look fine… until mold shows up months later.
6️⃣ Simple habits that help a lot
Keep the duct short and straight, insulate it in cold areas, and let the fan run for 15–30 minutes after showers. A small timer switch can save years of headaches.
Relatable moment 😅
Many people install a fan and assume the job is done… only to discover later that the moisture was never actually leaving the house. A good vent path makes all the difference.