Uninsulated fan ducts in an attic (C) Daniel FriedmanBath Exhaust Fan Duct Insulation
Why & how should we insulate the exhaust duct on a bathroom exhaust fan system?

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Bath Exhaust Fan Duct Insulation: how should we insulate the exhaust duct on a bathroom exhaust fan system to prevent condensation and leaks into the building or wall?

This article series explains how to install bathroom exhaust fans or vents, the vent ducting, the vent termination at the wall, soffit or roof, vent fan wiring, bath vent duct insulation, bath vent lengths, clearances, routing, and we answer just about any other bathroom ventilation design or installation question you may have.

Green links show where you are. © Copyright 2015 InspectApedia.com, All Rights Reserved.

Bathroom Vent Fan Ductwork Insulation

Insulate the bathroom exhaust vent fan ducts: In un-conditioned space such as an attic, where otherwise your fan duct will be exposed to cold attic air in winter, use insulated solid metal ducting or insulated flex duct.

Uninsulated fan ducts in an attic (C) Daniel Friedman

We insulate the bath vent ductwork to minimize the condensation that will otherwise occur as warm moist bathroom exhaust air passes through cool ductwork in the building attic or roof cavity.

Our photo shows a long routing of bath vent fan ducts across an attic floor to an exit at the building soffit or eaves and the condensation of moisture in such vent lines.

These ducts should be insulated (or replaced with pre-fab insulated ductwork or flexduct), and a better installation would have shortened that very long duct as much as possible, exiting to a soffit closer to the bathroom.

Metal bath exhaust fan duct installation in new construction (C) Daniel Friedman Bath exhaust fan in insulated ceiling after foam insulation installation (C) Daniel Friedman

Above we illustrate bath exhaust vent ducting before and after it is covered by a spray foam insulation job in a cathedral ceiling.

Watch out: we do not recommend purchasing vent ducts with insulation on the duct interior. Although fiberglass-lined HVAC ducts are widely used in heating and air conditioning systems as well as in heat recovery ventilator systems, for a standard bath exhaust fan vent duct, the combination of permeable fiberglass or other insulating material and very high moisture levels is asking for mold or other trouble inside the vent line.


Continue reading at BATHROOM VENT DUCT SLOPE or select a topic from the More Reading links shown below.

Suggested citation for this web page

BATHROOM VENT DUCT INSULATION at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

More Reading

Green link shows where you are in this article series.


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

HTML Comment Box is loading comments...

Technical Reviewers & References

Publisher's Google+ Page by Daniel Friedman

Click to Show or Hide Citations & References

Support InspectApedia.com & See Fewer Advertisements

From Google's Contributor website: Contribute a few dollars each month. See fewer ads. The money you contribute helps fund the sites you visit.

Google-Contributor supports websites while reducing advertisements. You can support InspectApedia with a contribution of any amount you wish. Or you can contribute nothing and we'll still keep our website free to all readers - supported by advertising. Either approach is OK.