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Bath vent fan codes, installation, diagnosis & repair:
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.
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. We also describe bathroom vent fan ducts, where to route vent air, duct condensation, ceiling leaks; Photographs of bad or ineffective bath fan installations.
We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.
Why is Bathroom Ventilation Needed?
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,
moisture, odors, and VOCs from aerosols and various personal
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.
2015 IECC Section R403.6 Mechanical Ventilation (Mandatory)
The building shall be provided with ventilation that meets the requirements of the International Residential Code or International Mechanical Code, as applicable, or with other approved means of ventilation. Outdoor air intakes and exhaust shall have automatic or gravity dampers that close when the ventilation system is not operating.
Guide to Installing Bathroom Vent Fans & Fan Ductwork
Some signs of excessive, uncontrolled bathroom moisture include:
- Stains, thermal tracking, or mold growth on bathroom walls and ceilings, possibly also on bath vanities and cabinets
- Damaged bathroom window trim
- Bathroom window condensation, and frost forming on bathroom windows during freezing weather
- Frost found in the attic on the roof underside over the bathroom area during freezing weather
- Stains and mold growth found on the roof sheathing in attics or roof cavities over bathrooms
- Damaged or curled roof shingles concentrated over a bathroom
- Leak stains in bathroom ceilings, especially around ceiling penetrations for light fixtures or ceiling vent fans
Bathroom vent fan duct installation & routing suggestions begin just below
at BATHROOM VENT DUCT MATERIALS
Also see BATH KITCHEN VENT DUCT SHARING
Bathroom vent fan duct materials: flex duct vs solid metal
IRC M1506.1 Duct Construction
Where exhaust duct construction is not specified in this chapter, construction shall comply with Chapter 16.
IRC Section M1601 Duct Construction
IRC M1601.1 Duct Design
Duct systems serving heating, cooling and ventilation equipment shall be installed in accordance with the provisions of this section and ACCA Manual D, the appliance manufacturer’s installation instructions or other approved methods.
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.
IRC M1601.1.1 Above-Ground Duct Systems
Above-ground duct systems shall conform to the following:
- Equipment connected to duct systems shall be designed to limit discharge air temperature to not greater than 250°F (121°C).
- Factory-made ducts shall be listed and labeled in accordance with UL 181 and installed in accordance with the manufacturer’s instructions.
- Fibrous glass duct construction shall conform to the SMACNA Fibrous Glass Duct Construction Standards or NAIMA Fibrous Glass Duct Construction Standards.
- Field-fabricated and shop-fabricated metal and flexible duct constructions shall conform to the SMACNA HVAC Duct Construction Standards‒Metal and Flexible except as allowed by Table M1601.1.1. Galvanized steel shall conform to ASTM A 653.
- The use of gypsum products to construct return air ducts or plenums is permitted, provided that the air temperature does not exceed 125°F (52°C) and exposed surfaces are not subject to condensation.
- Duct systems shall be constructed of materials having a flame spread index of not greater than 200.
- Stud wall cavities and the spaces between solid floor joists to be used as air plenums shall comply with the following conditions:
- These cavities or spaces shall not be used as a plenum for supply air.
- These cavities or spaces shall not be part of a required fire-resistance-rated assembly.
- Stud wall cavities shall not convey air from more than one floor level.
- Stud wall cavities and joist-space plenums shall be isolated from adjacent concealed spaces by tight-fitting fireblocking in accordance with Section R602.8.
- Stud wall cavities in the outside walls of building envelope assemblies shall not be utilized as air plenums.
Source: IRC SECTION M1601 DUCT CONSTRUCTION (2015) [PDF] Utah state code, retrieved 2019/10/03 original source: https://up.codes/viewer/utah/irc-2015/chapter/16/duct-systems#16 codes as adopted by the state of Utah
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 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 Venting Codes & Vent Fan Codes
Bathroom Ventilation Requirements Summary
The model building codes adopted by most jurisdictions typically require bathroom ventilation to be provided either by an operable window (3 sq. ft. or greater) or by mechanical means – a bathroom vent fan (20 continuous or 50 cfm intermittent, vented to the building exterior.
Lighting as well as mechanical ventilation are both required where there is not an adequate operable window.
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 CODES SPECS – home.
The model ventilation codes, building codes, mechanical codes, plumbing codes do not generally discuss exhaust vent duct direction and routing such as “up” or “down” through attics or crawl areas, but all of the model codes require that the vent fan must exhaust to the building exterior:
- Residential code: R303 Ventilation air from the space shall be exhausted directly to the outside.
- Mechanical code: M1501.1 Outdoor discharge. The air removed by every mechanical exhaust system shall be discharged to the outdoors.
- M1507.1 General. Where toilet rooms and bathrooms are mechanically ventilated, the ventilation equipment shall be installed in accordance with this section.
- M1507.2 Recirculation of air. Exhaust air from bathrooms and toilet rooms shall not be recirculated within a residence or to another dwelling unit and shall be exhausted directly to the outdoors.
- M1507.3 Exhaust Rates for Residential Dwellings – Oregon 2011 Code adopted from IRC
Table M1507.3 Exhaust Rates for Residential Dwellings: Kitchens / Bathrooms – Toilet Rooms
[Click to enlarge any image]
Source: M1507.4 Prescriptive Exhaust Duct Sizing – Oregon 2011 Code adopted from IRC
Table M1507.4 Prescriptive Exhaust Duct Sizing
Watch out: be sure to see the duct length limits given at BATHROOM VENT DUCT LENGTHS
IRC RESIDENTIAL SPECIALTY CODE – CHAPTER 15 EXHAUST SYSTEMS 2017 FLORIDA [PDF] modeled from the International Residential Code or IRC
IRC RESIDENTIAL SPECIALTY CODE – CHAPTER 15 EXHAUST SYSTEMS 2011 OREGON [PDF] modeled from the International Residential Code or IRC
M1507.4 Local exhaust rates
Local exhaust systems shall be designed to have the capacity to exhaust the minimum air flow rate determined in accordance with Table M1507.4.
TABLE M1507.4 – MINIMUM REQUIRED LOCAL EXHAUST RATES FOR ONE- AND TWO-FAMILY DWELLINGS
Area to be
|Kitchens||100 CFM intermittent or 25 CFM continuous|
|Bathrooms-Toilet Rooms||Mechanical exhaust capacity of 50 CFM intermittent or 20 CFM continuous|
Note that for bathrooms the ventilation specification is for mechanical exhaust and is not considering ventilation through a bathroom window.
Bathroom Venting Exhaust Fan CFM Adequacy
The model codes are specifying the minimum bathroom vent fan capacity needed. If your bathroom includes a steam bath, steam shower, or jetted tub, sources of additional moisture, you will need to increase the total bathroom exhaust vent capacity in CFM.
Industry experts recommend 60 cfm to 80 cfm for small bathrooms and 200 to 300 cfm for a large bathroom with a steam generator
. And if your vent fan ducting is long or includes bends that too will require added fan capacity.
Watch out: higher CFM bath fans, and some low-cost cfm bathroom ventilators can be so noisy that nobody wants to operate them – leading to indoor moisture, mold, even rot problems. Details about how to determine the necessary vent fan capacity in cubic feet per minute and about bath vent fan noise control options are
at BATHROOM VENT FAN SIZING & NOISE RATINGS
Watch out: while recirculating or in my view faux-vent fans are sold by some building suppliers, they are not permitted for bathrooms, are ineffective, and will probably leave the bathroom wet and smelly.
2018 Bath Exhaust Vent Duct Lengths
Exhaust duct length vs diameter vs CFM per the building codes and discussion of use of fan duct calculators are given
at BATHROOM VENT DUCT LENGTHS
2006 ICC Ventilation Code, Chapter 4, Ventilation
The U.S. state of Virginia adopted the ICC model ventilation code that we cite here.
Required Bathroom vent fan ventilation rate in CFM
This ventilation code specifies a bathroom exhaust airflow rate for toilet rooms and bathrooms (not served by a window of adequate size) 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]
2018, 2015, 2009 & 2006 IRC Bathroom Ventilation Code Excerpts for Ventilation
Where no window: 20 cfm continuous, 50 cfm intermittent, vent to building exterior
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.
See BATHROOM VENT DUCT TERMINATION for details about how to terminate the bath exhaust vent duct.
Example Model Ventilation Codes
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:
§[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
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 & Kitchen Vent Air-Flow Measurements & Standards
Question: can you measure the air flow at my New York City Apartment Kitchen & Bathroom Vents to Show They’re Inadequate?
I come to you because I need a professional of HVAC.
I moved in in a new building on Harlem – NYC – mid December, and since then I have a problem with the exhaust fans in the kitchen and the bathroom. The strength of the aspiration seems very low and so the fans are not efficient. (ie: the bathroom stays humid)
I asked the management of the building to take care of this but they just did a test with a tissue that stays on the grill. But this test does not mean the strength is OK.
I want to be sure I am right, so I would like to know if you guys can come over to measure the flow of the air with a flood hood or another dedicated appliance.
Do you know a serious, reliable, reasonable price contractor who could provide this service ? – Anonymous by private email 2017/08/01
Sketch above was provided courtesy Carson Dunlop Associates a Toronto home inspection, education, and report-writing firm.
Reply: Recommendations & OPINION
A tissue is a reasonable way to see which way air is moving – in or out of a register, as we discuss
at RETURN AIR, INCREASE,
or in and out of a window in a high-rise building (photo shown here and discussed further
at AIR MOVEMENT in BUILDINGS).
But it is impossible to translate the thin tissue of that observation to an objective measure of air flow rates nor to a reliable statement about the adequacy of a vent system since even the most slight air flow will move a light tissue against the intake grille of the vent.
In NYC there are quite a few HVAC companies, some of whom might be willing to send over someone to measure your exhaust fan performance but frankly I’m doubtful that the cost is worth the benefit.
Exhaust fans in the U.S., especially in older buildings, are typically of very modest capacity – to put it politely. Historically or at least before the city’s adoption of modern energy and ventilation codes, New York City (NYC) buildings vented into an air-shaft, by windows or by convection and without electricity.
I suspect the cost of even a simple site visit and report (probably $250 to $400.) would cost not much less than the cost to install a higher capacity fan, even more-likely if the higher-capacity fan were also a low-sones-rated (that is to say less noisy) unit. A Panasonic ceiling vent fan unit itself is about $125. U.S. + installation. Figure $400+ in NYC.
Most of those HVAC engineering companies are interested in working on larger projects involving building air conditioners and are not interested in vent fan systems in an individual apartment.
A local HVAC installation company (not an engineering firm per-se) may have a qualified design engineer on staff who could do what you ask, but they too are not very interested in small jobs and may price consulting accordingly -unless you are going to install a more expensive air-to-air heat exchanger unit (HRV or a more-sophisticated “ERV” – energy (enthalph) recovery unit, – loosely-called “heat -recovery-ventilators”.)
Here is an NY City company familiar with ventilation codes – you could call to see what they charge and what they will do (and let me know what you’re told)
- New York Engineers, 275 West 39th Street, 2nd Floor New York, NY 10018 212-575-5300, http://www.ny-engineers.com/blog/ventilation-options-for-residential-buildings
If you own or intend to have a long term lease on the apartment, those improvements may be worth doing.
But when you rent, usually the landlord is not legally bound to improve your bath venting. The landlord may not be complying with city mechanical codes on ventilation (given below) but they still may not be too anxious fix inadequate ventilation unless faced with a larger issue than one tenant who wants proper design, ventilation, and indoor air quality.
Note: For a helpful discussion of just what constitutes “adequate venitlation”, see Offermann, Francis (Bud) J., P.E., C.I.H., ASHRAE & Mark Nicas, Ph.D., MPH, C.I.H., USE WITH ADEQUATE VENTILATION ? [PDF], ASHRAE Journal, May 2018.
I suspect that only if you could make a case that the present unit is dangerous as a fire hazard or unsafe (creating an expensive mold contamination problem) might you get anywhere without having to hire a lawyer.
If you take a look in the ductwork and see an accumulation of grease in a kitchen exhaust I’d consider that a potential fire worry that might get action.
You could buy your building manager an air flow measuring device –
see AIR FLOW MEASUREMENT CFM –
for less than the cost of a service call. Then let your building super use the measuring tool instead of a piece of tissue – if they’re willing to do it. (The gift of the cfm tool might be taken as generous and prompt action or as annoying and … depending on personalities. )
Compare the readings at your kitchen and bath vents with what NY City building mechanical code requires:
- Kitchen ventilation fan requirements: 100 cfm (intermittent) or 25 cfm (continuous) (cfm = cubic feet per minute)
- Bathroom ventilation fan requirements: 50 cfm (intermittent) or 20 cfm (continuous)
At BUILDING CODE DOWNLOADS I provide links to New York City codes that specify that mechanical ventilation is required for kitchens and bathrooms regardless of whether there is a window or not (Chapter 12, INTERIOR ENVIRONMENT) and a link to the city’s mechanical code where the engineering firm whose page I gave above got those vent-rate requirements. There you’ll find
- NEW YORK CITY MECHANICAL CODE (2008) [PDF] adapted from the ICC Mechanical code, Chapter 4, VENTILATION, retrieved 2017/08/01,original source: http://www2.iccsafe.org/states/newyorkcity/Mechanical/PDFs/Chapter%204_Ventilation.pdf
- NEW YORK CITY CODE: INTERIOR ENVIRONMENT [PDF],. Chapter 12, INTERIOR ENVIRONMENT, retrieved 2017/08/01,original source: http://www.nyc.gov/html/dob/apps/pdf_viewer/ viewer.html?file=2014CC_BC_Chapter_12_Interior_Environment.pdf§ion=conscode_2014
1201.1 Scope.The provisions of this chapter shall govern ventilation, temperature control, lighting, yards and courts, sound transmission, room dimensions, surrounding materials and rodent proofing associated with the interior spaces of buildings
- NEW YORK STATE HVAC ENERGY CODE REQUIREMENTS [PDF] for Heating, Ventilation, & Air Conditioning Code & Specifications retrieved 2017/08/01, original source: https://www.dos.ny.gov/dcea/pdf/ Energy/RmanHVAC.pdf
and other codes and standards.
Also see more specifications for ventilation of baths and kitchens at
Bath Vent Fan Duct Duct Damage Protection
Protect 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.
Discussion of 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
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.
Bathroom Vent Fan Ductwork Insulation
This topic has moved to a new article at BATHROOM VENT DUCT INSULATION
Bathroom Vent Fan Duct Routing
Please see BATHROOM VENT DUCT ROUTING
Bath exhaust fan duct length specifications and restrictions are discussed separately
at BATHROOM VENT DUCT LENGTHS.
See BATHROOM VENT DUCT TERMINATION for details about how to terminate the bath exhaust vent duct. The fan must vent to the building exterior.
Bath Exhaust Fans Routed Up Through the Roof
This 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
Reader Q&A – also see the FAQs series linked-to below
If I understand your original question, you have a bath exhaust that is discharging into a roof cavity or space not to outside.
In no case is it acceptable to just dump any exhaust fan directly into an attic. It needs to exhaust to the exterior.
this is only a toilet room, adjacent to the master bath which contains a ventilation fan that vents externally. How are half bathrooms handled? Any differently? Our house passed final inspection when the house was built 7 years ago, but failed in this area when the buyers hired a home inspector.
Bath exhaust vents need to be directed to the outdoors, not into an enclosed building cavity.
The answer to your code question is given in the article above on this page
See BATHROOM VENT CODES
Is it okay to vent a ceiling fan into the attic for just a toilet room? What is the IRC code referencing this?
The exhaust vent duct should not terminate in an attic or roof space; it needs to vent to the building exterior.
What is California code on bathroom exhaust fans, primarily at the point of how the tubing and what tubing is connected to. Is it legal to have the flex tube vented to a dormer vent but the tube ends 1ft short of the actual vent and not connected directly to it?
Its ok if the length, slope, etc. are following the manufacturer’s guidelines.
Is it acceptable to use 4″PVC pipe as an exhaust duct in a small Powder Room?
It will go straight up through an insulated interior wall into the attic, and then outside via roof vent installed by a roofer.
Or do I need to use a duct of other material ? Please advise.
Thank you so much for asking. I’m embarrassed to report that reading our two main articles on bath exhaust fan duct length here and at the link I give below, I found no clear answer.
The reason that there is no one right answer to “how long can I make my bath exhaust vent duct run?” is that … it depends on
– the fan model (its size and CFM rating)
– the vent material (smooth vs. corrugated or worse)
– the vent diameter
– the number of elbows
– the required or “design” flow rate in CFM (from your local code, such as 40 CFM).
The exhaust vent must comply with local codes that in turn are typically adopted versions of
the 2015 IRC Section M1506.2
or the 2018 IRC Section M1504.2 (ft)
So we need to know the Brand and model of your exhaust fan and then to look at that manufacturer’s specific installation instructions (that will include duct length and length-equivalent numbers for each elbow or bend)
Bath exhaust fan duct length specifications and restrictions are discussed further at BATHROOM VENT DUCT LENGTHS. inspectapedia.com/ventilation/Bathroom_Vent_Duct_Lengths.php
Also, though I emphasize that following the instructions for your specific exhaust fan are the first place to check, the fan manufacturers also include exhaust vent fan length calculators.
For example Broan’s calculator is at www.broan.com/Support/Specifier-Tools/Allowable-Duct-Length-Calculator
There you’ll see that for higher CFM flow rates some fan models won’t be acceptable period while others (according to Broan and I doubt this) are shown as “NL” or “no limit on length”
Example: for a 40 CFM flow rate and a 3″ smooth duct diameter and using just 2 elbows
Broan Fan Model EZ80N can run up to 34 ft.
But this isn’t enough: Industry experts recommend 60 cfm to 80 cfm for small bathrooms and 200 to 300 cfm for a large bathroom with a steam generator
When we change the design CFM to 60 we see that with a 3″ duct this fan WILL NOT WORK period.
When we then change the DUCT DIAMETER to 5 inches, the calculator says yeah, you’re good, no limit.
Watch out: using these fan calculators you can quickly get in trouble: that means having a fan that won’t actually work or that will give a fire hazard – if you do not watch every parameter you enter with great care. Some of the fan models will show “no limit” to duct length (that I question) but look again: the calculator may have changed the vent duct diameter from 3″ up to 7″ or 8″.
I’ll add more data tables, code citations and examples to the article above.
Thanks for asking
Finishing out basement bathroom the only wall I can run my exhaust outside is 32’ away can I use 3” glued pvc and can I have a run of this distance
I’m not sure what kind of fan we’re discussing, Matt, but certainly if an exhaust fan is too close to a supply or return air register for a heating system, when the exhaust is running it may interfere with the delivery of heated air to the space.
A typical guideline will require that the exhaust fan inlet be at least two meters or six feet away from the hearest HVAC register. Some inspectors require a 10 foot separation. Section M1602.2 of the 2006 IRC is an example.
Is there a requirement for seperation between ac/ heat registers and the exhaust fan housing
You cannot necessarily put all plumbing vents out through a roof at a single point – the distances involved may be too great to jam all of the plumbing vents together – it depends on the building size, plumbing routing, etc.
Is it possible and up to code to put all you vents together so there is only one stack coming out of the roof
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
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
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Technical Reviewers & References
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- “Panasonic® Ventilating Fan Installation Instructions, FV-05VQ3, FV-08VQ3, FV11VQ3, FV-15VQ3”, X120-4-8189Panasonic Consumer Electronics Co., Div. of Panasonic Corp. of North America, One Panasonic Way, Seacaucus NJ 07094 & Panasonic Canada, Inc., 5770 Ambler Dr., Imssissauga, ON L4W 2T3, Website: www.panasonic.com, retrieved 4/7/14
- “Brink Renovent HR Installation and Operation Manual”, Brink Climate Systems, P.O. box 11
NL-7950 AA Staphorst
+31 522 46 99 44
www.brinkclimatesystems.nl retrieved 4/7/14 This is the installation guide for medium & large Brink Renovent HR systems.
- “Installation Instruction, Heat Recovery Unit, Renovent Small”, Brink Climate Systems, P.O. box 11
NL-7950 AA Staphorst
+31 522 46 99 44
www.brinkclimatesystems.nl retrieved 4/7/14 This is the installation guide for the small Brink Renovent HR system. [copy on file]
- “About the House – Bathroom Vents”, Henri deMarne, New England Builder, November 1985
- “Bathroom Vent Fan Beats Open Window”, James Dulley, Poughkeepsie Journal, 11/4/1987 p. 12D.
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 [email protected]
- John Cranor [Website: /www.house-whisperer.com ] is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-873-8534 or by Email: [email protected]
- Eric Galow, Galow Homes, Lagrangeville, NY. Mr. Galow can be reached by email: [email protected] or by telephone: 914-474-6613. Mr. Galow specializes in residential construction including both new homes and repairs, renovations, and additions.
References for Bathroom Vent Fan Installation
- Fantech Installation, Operation, and Maintenance Manual, PB Series Premium Bath Fans. These fan models use a remote fan motor and
are available in 4″ duct and 6″ duct models. Web search 7/26/11 – original source http://fantech.net/docs-resi/412889-pb-install.pdf
Fantech in the United States
10048 Industrial Blvd.,
Lenexa, KS 66215
Phone: 800.747.1762; 913.752.6000
Fax: 800.487.9915; 913.752.6466
www.fantech.net; [email protected]
Fantech in Canada
50 Kanalflakt Way,
Bouctouche, NB E4S 3M5
Phone: 800.565.3548; 506.743.9500
Fax: 877.747.8116; 506.743.9600
www.fantech.ca; [email protected]
- Nutone Bathroom Exhaust Fan/Light Combination Installation Instructions, Model 8663RP, 8673RP, 8664RP suitable for use
in shower or tub enclosure when used with GFCI protected branch circuit. Suitable for use in insulated ceilings.
Nutone, 4820 Red Bank Road, Cincinnati, Ohio 45227, web search 07/27/2011, original source:
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
- Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews – InspectAPedia.
- “Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] – “, U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print
- “Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] – “, U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870
- “Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] – “, U.S. Department of Energy
- “Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] – “, U.S. Department of Energy
- “Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] – “, U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900
- “Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] – “, U.S. Department of Energy
- “Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] – “, U.S. Department of Energy
- Fiberglass: Indoor Air Quality Investigations: Health Concerns About Airborne Fiberglass: Fiberglass in Indoor Air from HVAC ducts, and Building Insulation
- Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
- “Weather-Resistive Barriers [copy on file as /interiors/Weather_Resistant_Barriers_DOE.pdf ] – “, how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
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