Bathroom ceiling vent fan, heater, light combination (C) Daniel Friedman Bathroom Ventilation Fan Installation / Repair

  • BATHROOM VENTILATION - CONTENTS: How to install, specify or improve bathroom venting, reduce indoor condensation, avoid bathroom mold. Bathroom vent fans, required bath vent fan capacity, fan noise and sones. Bathroom vent fan ducts, where to route vent air, duct condensation, ceiling leaks; Photographs of bad or ineffective bath fan installations
  • POST a QUESTION or READ FAQs about bathroom vent fan and fan ducting installation procedures, codes, standards
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Bath vent fan installation, troubleshooting, repair:

This article series describes how to install bathroom ventilation systems, fans, ducts, terminations. We include bathroom venting code citations and the text also explains why bathroom vent fans are needed and describes good bath vent fan choices, necessary fan capacity, and good bath vent fan and vent-duct installation details. We discuss bathroom exhaust vent codes, specifications, advice.

We explain 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. We discuss bath vent routing, insulation, slope, termination, airflow rate requirements and other specifications.

Green links show where you are. © Copyright 2017, All Rights Reserved.

Why is Bathroom Ventilation Needed?

Wet attic around bad bath vent fan (C) Daniel Friedman

Ventilation in bathrooms is important to prevent moisture damage to wall and ceiling surfaces, decay of wood trim, saturation of building insulation, and mold contamination.

And as Steven Bliss writes in a companion article at BATHROOM VENTILATION DESIGN, "Bathrooms produce moisture, odors, and VOCs from aerosols and various personal hygiene products. Effective spot ventilation in these areas is critical for maintaining healthy levels of indoor humidity levels and an overall healthy indoor environment."

Especially in bathrooms where a shower is used, large amounts of moisture are added to room air and are concentrated in this area.

Our photo (above-left) shows a horrible bathroom ceiling vent fan ductwork job: multiple ducts sprawl around in the attic, all joining to terminate at an attempted through-roof vent that has fallen back into the attic.

Notice how wet the roof sheathing is? These conditions are inviting an attic mold problem too.

Guide to Installing Bathroom Vent Fans & Fan Ductwork

Bath vent spills into attic (C) D Friedman

Some signs of excessive, uncontrolled bathroom moisture include:

Bathroom vent fan duct installation & routing suggestions begin just below at BATHROOM VENT DUCT MATERIALS

Bathroom vent fan duct materials: flex duct vs solid metal

Vent fan spilling into attic (C) D Friedman Uninsulated fan ducts in an attic (C) Daniel Friedman

Flexible plastic vent fan ductwork: shown at above left is a common use of un insulated, flexible ventilation fan duct. In this installation the duct is improperly installed, spilling directly into the attic space of the building. This duct material is least costly at the time of installation but may be most costly when a combination of accumulated condensation and duct damage leaks into the building insulation or ceiling cavity.

Flexible metallic exhaust fan ductwork: shown at above right is flexible metal exhaust fan ductwork. This material is more smooth-surfaced than the plastic product shown at above left and by its flexibility, can eliminate the need to install many elbows in the system. The installation shown is too long and should have been insulated.

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

Metal vent ducts: kitchen vent fans require, and good bath vent duct design also uses solid metal ducting, not flexible "dryer vent" material. Solid ductwork has a smoother interior surface that improves airflow, though it is indeed more trouble and a bit more cost to install.

Solid metal vs flex duct for kitchen and bath vent fans: For optimum venting use insulated 4" or larger metal ductwork rather than flexduct that may sag, giving you areas that collect water and risk leaking into a ceiling below. Kitchen vent fans require metal ductwork for fire safety.

Our photo at above left illustrates a solid metal bathroom exhaust duct along with the bath vent housing installed in a cathedral ceiling during new construction. The ceiling cavity between the I-Joists was later insulated with solid foam, as shown at above right.

Because this is a sloped cathedral ceiling it was not possible to slope the fan ductwork back down towards the shower below the fan. Instead we vented this fan out through the soffit in the roof eaves. (/ventilation/Bathroom_Vent_Termination.php)

Smooth metal duct also maximizes vent fan airflow performance. But flex duct and insulated flex duct are approved by bath vent fan manufacturers are very widely used for fan venting because of its ease of installation and low cost, as we describe next.

Question: using spray foam to seal around a bathroom vent fan

(Mar 12, 2014) John said:

Hi. I sprayed insulation foam ( not the fire block ) around the bathroom vent fan in an attempt to seal small air leak from the attic . Is this a fire hazard ? Thank you



You should be OK if - the following:

- foam did not enter the fan enclosure
- the fan installation data including stickers inside the fixture specify that it can be installed in direct contact with building insulation.

I'd have preferred using a fire-resistant foam, but if the above conditions are met you should be ok. Take a look at the bathroom vent fan duct installation in the photographs above and you'll see a successful bath vent installation in a foam-insulated cathedral ceiling.

Bathroom Vent Fan Duct Routing


Uninsulated fan ducts in an attic (C) Daniel Friedman

Bath exhaust fan duct length specifications and restrictions are discussed separately at BATHROOM VENT DUCT LENGTHS.

Bath Exhaust Fans Routed Up Through the Roof

Sources of makeup air for a bath vent fan (C) Daniel FriedmanThis discussion is now found at BATHROOM VENT UP THROUGH ROOF

I prefer to run a bath vent to outdoors via a horizontal line that goes across an attic and out through a gable-end wall or one that vents down and outside through a roof overhang or soffit. The vent run needs to be designed to drain any condensate outside not back into the bathroom ceiling; in a freezing climate I'd insulate such a vent line as well; If we run a bath vent vertically up through a roof we have two risks I'd prefer to avoid:

A vertical bath exhaust fan duct run guarantees that any condensation runs back down into the fan (risking damaging the wiring or fan motor) and back into the bath or bath ceiling.

The vertical run also means another roof penetration. I prefer to minimize the number of roof penetrations on any building since every penetration is a potential leak point, more so if the penetration flashing is not installed correctly.

Also, for bathrooms over 100 sq ft, the HVI recommends a ventilation rate based on the number and type of fixtures as shown in Table 6-12 - data discussed in more detail at BATHROOM VENTILATION DESIGN

Bathroom Vent Fan Routing Down & Out Through a Floor or Crawl Space

We moved this discussion to a full article at BATHROOM VENT DOWN THROUGH FLOOR / CRAWL AREA

Bathroom Venting Codes

The model building codes adopted by most jurisdictions typically require bathroom ventilation to be provided either by an operable window or by mechanical means - a bathroom vent fan. Below we excerpt key bathroom ventilation code specifications. More complete bathroom venting design and installation specifications such as discussions of vent duct lengths, insulation, slope, air supply, wiring, are listed at BATHROOM VENTILATION - home.

The model ventilation codes do not generally discuss exhaust vent duct direction and routing such as "up" or "down" through attics or crawl areas.

2006 ICC Ventilation Code, Chapter 4, Ventilation

The U.S. state of Virginia adopted the ICC model ventilation code that we cite here. This code specifies a bathroom exhaust airflow rate for toilet rooms and bathrooms of

25 or 50 cfm/ft for hotels, motels, resorts and dormitories,

and a slightly more modest 20 / 50 cfm for private dwellings.

Rates are per room unless otherwise indicated. The higher rate shall be provided where the exhaust system is designed to operate intermittently. The lower rate shall be permitted where the exhaust system is designed to operate continuously during normal hours of use. - [Table 403.3, Minimum Ventilation Rates]

This model ventilation code also specifies that the ventilation system

Exhaust openings shall have a minimum and maximum size in louvers, grilles and screens, measured in any direction of not less than 1/4" and not more than 1/2"

Intake openings in residential occupancies shall be not less than 1/4" and not more than 1/2"

Intake openings in other than residential occupancies shall be not less than 1/4" and not more than 1" - [Table 401.5, Opening Sizes in Louvers, Grilles and Screens Protecting Outdoor Exhaust and Air Intake Openings]

2006 IRC Bathroom Ventilation Code

The 2006 (or later) International Residential Code IRC R303.3 Bathroom Ventilation - requires that

when natural ventilation requirements (3 sq ft of windows 50% operable) can't be met,

the bath should be vented by either a 20 cfm continuous vent fan or a 50 cfm vent fan that is intermittent (or switched).

Exhausting of the bath vent fan must indeed be to the building exterior.

Exhaust Air from toilet rooms and bathrooms shall not discharge into attic, crawl space or other areas inside building.

New York City Title 27 / Subchapter 12: Light, Heat, Ventilation & Noise Control Code

A very detailed building code guideline beyond the IRC I cited below is the New York City housing code from which I excerpt this Bathroom Ventilation Code:

ยง[C26-1207.3] 27-759 Bathrooms and toilet rooms.- Bathrooms and toilet rooms shall be ventilated as follows:

(a) When ventilated by natural means, the natural ventilation sources shall comply with section 27-749 of article six of this subchapter and shall have an unobstructed free area of at least five percent of the floor area. In no case shall the net free area of the ventilation sources be less than one and one-half square feet except that in occupancy groups H-1 and H-2, provided the ventilation opening conforming with section 27-749 of article six of this subchapter may be in a vent shaft provided that the net free area of the opening is not less than three square feet. The vent shaft cross-sectional area shall be increased by one-fifth of a square foot for every foot of height, but shall not be less than nine square feet in area and open to the outer air at the top; or, the vent shaft may be open at the sides above the roof with louvers providing an equivalent net free area at the top, equal to the area of the shaft.

(b) By individual vent shafts or ducts constructed of noncombustible materials with a minimum cross-sectional area of one square foot and one-third additional square foot for each additional water closet or urinal above two in number. The upper termination of such ducts shall be equipped with a wind-blown ventilator cap.

(c) When a bathroom or toilet room is not ventilated by natural ventilation as required by this section, it shall be mechanically ventilated as follows:

(1) Rooms containing only one water closet or urinal shall be mechanically ventilated by an exhaust system capable of exhausting at least fifty cubic feet of air per minute. Means shall be provided for air ingress by louvres in the door, by undercutting the door, or by transfer ducts, grilles, or other openings.

(2) Rooms containing more than one water closet or urinal, and any auxiliary spaces such as those used in hand basins, slop sinks, and locker rooms, shall be mechanically ventilated by an independent exhaust system capable of exhausting at least forty cubic feet of air per minute per water closet or urinal. The outdoor air supply shall conform to the requirements of article seven of this subchapter.

(3) Toilet exhaust systems shall be arranged to expel air directly to the outdoors.

Bathroom Vent Fan Ductwork Insulation

This topic has moved to a new article at BATHROOM VENT DUCT INSULATION

Proper Bath Vent Fan Duct Slope & Slope Direction

This topic has moved to a new article at BATHROOM VENT DUCT SLOPE

Bath Vent Fan Duct Terminations & Clearance Distances

This topic has moved to a new article at BATHROOM VENT DUCT TERMINATION

Bath Vent Fan Duct Termination Clearance Distances

This topic has moved to a new article at BATHROOM VENT CLEARANCES

Bath Vent Fan Duct Duct Damage Protection

Damaged bath exhaust vent duct (C) D FriedmanProtect the bath exhaust fan exhaust vent from damage during installation. Our photo (left) illustrates damage we found in a building ceiling where the exhaust vent duct had been torn during installation. A result was moisture and ultimately mold contamination in the bathroom ceiling.

Bathroom Vent Fan Duct Length Specifications

Bathroom vent fan duct length restrictions: keep the fan duct length as short and straight as possible.

Some manufacturers require a minimum distance between the duct outdoor termination and the fan assembly; a review of installation guides for several bathroom vent fan models did not come up with a maximum distance. Long vent fan duct runs reduce the ability of the fan to move air.

Details about maximum and minimum bath fan duct run distances or lengths are at BATHROOM VENT DUCT LENGTHS.

Bathroom Exhaust Fan Heat Recovery Ventilator Systems

This bathroom vent fan topic has moved to BATH EXHAUST FAN HEAT RECOVERY

Bath Vent Fan Wiring Connections

Simple fan only wiring for a Nutone Model 8814R and similar bath vent fans (C)  adapted from Nutone Typically the bathroom vent fan motor is powered by the bathroom ceiling light fixture circuit; some installers, particularly in hotels or rental units, hard-wire the bath exhaust vent fan to force it on when the bathroom ceiling light is on - thus assuring that the vent fan is in fact used. If the bath vent fan is noisy this forced-on status can annoy everybody.

In the simplest case there will be just three fan wires to connect: black to black (the hot or live or power wire), white to white (the neutral wire), and ground to ground, typically a bare ground in the house wiring to a green ground wire in the fan housing wiring set.

The most general fan wiring instructions will state: "Hook up the bath vent fan wiring by removing the electrical junction box cover. Next connect the house wires to the fan wires: ground to ground, neutral white to neutral white, and hot black to hot black."

[Click to enlarge any image]

But when the fan includes also a light and perhaps an electric heater there are actually three circuits to complete, each with its own controlling switch.

At BATHROOM FAN WIRING you will find detailed electrical wiring connections for a typical fan, light, & heater combination vent fan system, adapted from installation instructions for the Delta Breez Model RAD80L installation manual and other bath fan installation guides cited there.

Article Series Contents


Continue reading at BATHROOM VENTILATION DESIGN or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.







Suggested citation for this web page

BATHROOM VENTILATION at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


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

Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman