The short answer
Performance is essentially identical when both are designed correctly. Interior routing hides the pipe and protects it from sun and weather but costs more and requires a usable chase. Exterior routing is faster and cheaper but puts a visible white pipe on the side of your house.
Side by side
| Interior routing | Exterior routing | |
|---|---|---|
| Appearance | Pipe hidden inside a closet, chase, or garage | Visible pipe on an exterior wall |
| Cost | Higher — more labor, possible drywall repair | Lower |
| Fan location | Attic or garage attic | Exterior wall, above grade |
| UV exposure | None | Requires UV-resistant pipe or paint |
| Condensate | Drains back to the suction point naturally | Needs correct slope; cold-climate freezing risk |
| Noise | Fan hum enters the attic; keep away from bedrooms | Fan hum is outside, but audible near windows |
| Serviceability | Requires attic access | Easy ladder access |
| Best for | New builds, remodels, appearance-sensitive homes | Retrofits, brick or stucco walls with no chase |
Where each route usually wins
Choose interior when
- A closet, mechanical chase, or garage corner offers a clean vertical path.
- The home's street-facing elevation matters to you or to a future listing.
- You want the pipe and fan protected from weather and sun.
Choose exterior when
- There is no practical interior chase without cutting finished space.
- The suction point is near an exterior wall on the far side of the house.
- You want to keep the cost and the disruption down.
- Service access matters more than appearance.
Requirements that apply either way
- 1The fan must be outside conditioned space so the pressurized side cannot leak indoors.
- 2The exhaust must terminate above the roof eave line.
- 3The termination must be at least 10 feet from any window, door, or air intake, and away from adjacent structures.
- 4Pipe must be sealed and supported so it does not sag and trap condensate.
- 5Exterior pipe must be UV resistant or painted with an approved coating.
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