Questions & answers on bath vent fan codes, installation, diagnosis & repair.

This article series describes how to install bathroom ventilation systems, fans, ducts, terminations.

Bathroom Exhaust Vent Fan Code & Installation Q&A

These FAQs on bathroom exhaust vent wiring, installation, capacity, ducting etc. were posted originally at BATHROOM VENTILATION CODES SPECS - you will want to review the bath vent installation guidelines there.\

Photo: using an LED type light over a shower, sealed from below for safety, wiring accessed from an attic above the shower area.

[Click to enlarge any image]

On 2020-10-17 by (mod) - New Mexico bathroom venting code

Lisa, New Mexico has adopted the Uniform Mechanical Code on bathroom venting with a few minor exceptions.

401.2 Ventilation Required

Every occupied space shall be ventilated by natural means in accordance with Section 402 or by mechanical means in accordance with Section 403.

Where the air infiltration rate in a dwelling unit is less than 5 air changes per hour when tested with a blower door at a pressure of 0.2-inch water column (50 Pa) in accordance with Section R402.4.1.2 of the International Energy Conservation Code, the dwelling unit shall be ventilated by mechanical means in accordance with Section 403.

Ambulatory care facilities and Group I-2 occupancies shall be ventilated by mechanical means in accordance with Section 407.

401.3 When Required

Ventilation shall be provided during the periods that the room or space is occupied.

Section 402 Natural Ventilation

Natural ventilation of an occupied space shall be through windows, doors, louvers or other openings to the outdoors. The operating mechanism for such openings shall be provided with ready access so that the openings are readily controllable by the building occupants

402.2 Ventilation Area Required

The minimum openable area to the outdoors shall be 4 percent of the floor area being ventilated.

Section 403 Mechanical Ventilation

403.1 Ventilation System

Mechanical ventilation shall be provided by a method of supply air and return or exhaust air except that mechanical ventilation air requirements for Group R-2, R-3 and R-4 occupancies three stories and less in height above grade plane shall be provided by an exhaust system, supply system or combination thereof.

The amount of supply air shall be approximately equal to the amount of return and exhaust air.

The system shall not be prohibited from producing negative or positive pressure. The system to convey ventilation air shall be designed and installed in accordance with Chapter 6.


Details from New Mexico's bathroom venting code:

New Mexico Building Code, 14.9.2.12 CHAPTER 4 VENTILATION AIR SUPPLY:

See this chapter of the UMC and add the following material to section 405.0 Evaporative cooling systems:

"Barometric relief dampers shall be installed on all new residential evaporative cooling systems to allow conditioned air from occupied spaces to exit the occupied space tiirough a discreet opening in tiie ceiling, allowing tiie required air change to pass tiirough tiie attic space to tiie outdoors.

The authority having jurisdiction shall determine whether relief dampers shall be required on retrofits. Barometric relief dampers shall not be required on flat roof construction. Water saving or water management pumps shall be installed on all new and replaced evaporative coolers."

[14.9.2.12 NMAC - Rp, 14.9.2.12 NMAC, 1-1-08, A, 2-24-081

14.9.2.13 CHAPTER 5 EXHAUST SYSTEMS: See tiiis chapter of the UMC except as provided below.

A. 504.3.2.2 Length limitation. See this section of the UMC except delete everything after the
words "total combined horizontal and vertical length" and substitute:

of 23 feet (7m) with two ninety- degree (90-) elbows and a full 4 inch (102 mm) vent cap opening, or 33 feet (10 m) with one ninety- degree (90-) elbow and a full 4 inch (102 mm) vent cap opening. Ten feet (3.05 m) shall be deducted for each additional ninety-degree (90-) elbow in excess of the number allowed.

B. 507.6 Hoods required. Add this new section:

hoods shall be installed at or above all commercial-type deep fat fryers, broilers, fry grills, steam-jacketed kettles, hot-top ranges, ovens, barbecues, rotisseries, dishwashing machines and similar equipment that produce comparable amounts of steam, smoke, grease, or heat in a food- processing establishment.

For the purposes of this section, a food- processing establishment includes any building or portion thereof used for the processing of food, but does not include a dwelling unit.

C . 511.3 Replacement air. See this section of the UMC except add the following:

windows and doors shall not be used for the purpose of providing replacement air. The exhaust and replacement air systems shall be connected by an electrical interlocking switch.

[14.9.2.13 NMAC - Rp, 14.9.2.13 NMAC, 1-1-081

504.6 Gypsum Wallboard Ducts. Bathroom and laundry room exhaust ducts may be of gypsum wallboard subject to the limitations of Section 602.1.

4.9.2.12CHAPTER 4 VENTILATION AIR SUPPLY:See this chapter of the UMC and add the following material to section

405.0 Evaporative cooling systems:

“Barometric relief dampers shall be installed on all new residential evaporative cooling systems to allow conditioned air from occupied spaces to exit the occupied space through a discreet opening in the ceiling, allowing the required air change to pass through the attic space to the outdoors.

The authority having jurisdiction shall determine whether relief dampersshall be required on retrofits.

Barometric relief dampers shall not be required on flat roof construction. Water saving or water management pumps shall be installed on all new and replaced evaporative coolers.”[14.9.2.12 NMAC -Rp, 14.9.2.12 NMAC, 8-1-11]14.9.2.13CHAPTER 5

EXHAUST SYSTEMS:See this chapter of the UMC except as provided below. 511.3 Replacement air.See this section of the UMC except add the following:

windows and doors shall not be used for the purpose of providing replacement air.

The exhaust and replacement air systems shall be connected by an electrical interlocking switch.

When using equipment that is not listed for make-up air, a device to sense continued air movement within the replacement air plenum shall be installed initiating a complete system shut-down if air-flow is interrupted.[14.9.2.13 NMAC -Rp, 14.9.2.13 NMAC, 8-1-11]

On 2020-10-17 by Lisa Wojcik

My previous question refers to multi-family residential (apartment building of greater than 3 stories).

Is a bathroom vent fan (electrical/mechanical) required by building code where there is a tub or shower and no window in New Mexico (Bernalillo County)? Can you please cite regulation section numbers?

On 2020-09-29 - by (mod) -

Glad to assist;

On 2020-09-29 by Katalin

thanks again! Love short answers :) Yes, we live in Ohio USA. I was curious and looked it up also and came to the same conclusion = what is ETL certified, complies also with UL (speaking of the US).

So unless there is a specific OHIO regulation which is against the general standards for overhead shower vent/light, we are good to go. That is definitively good news! Have a nice day and thanks for the quick and helpful support!

On 2020-09-28 by (mod) - ETL Compliance Listing explained

Thank you for a helpful follow-up question, Katalin: is an ETL Compliance Listing acceptable for a device being installed in my building?

Short answer: most-likely, yes.

Where is your home: Country & city? To avoid a hassle with your code compliance inspector you want to be sure that the certifications are acceptable in your country of device installation.

ETL is accepted in the U.S. and Canada; I'm not sure about Mexico, which, for some of you presidents out there, also is in North America!

ETL is a North American certifying agency that is probably perfectly fine if that's where your home is located. The difference between ETL and UL listings is princiipally that UL develops standards as well as providing testing for standards compliance while ETL performs only the latter. Both are OSHA certified and both are accepted in most North American building jurisdictions.

"The ETL Mark is proof of product compliance to North American safety standards. " provided by Intertek - https://www.intertek.com/marks/etl/

On 2020-09-28 by Katalin

Thanks so much for the detailed explanation! It looks good to me however the model i picked states ETL compliance for wet application... is that equivalent to UL compliance? Sorry if I seem hesitant but I’m not an expert and really need advice on the model I am asking about. Thanks again for your support!

On 2020-09-28 by (mod) - U.S. Electrical Code citations on installing a light and/or fan over a shower or bath tub

Katalin

Electrical code for installing a fan and light over a shower

You can install a combination fan & light in a shower ceiling provided

1. the light and fan are on a protected GFCI circuit
and

2. the specific light/fan product is designed UL-Listed, and stated by the manufacturer as suitable for a shower ceiling or wet location. It's not quite correct that you "can't put a fan in a shower area".

Here is an excerpt from the US NEC (2014) that is also found in the 2020 US National Electrical Code.

US NEC 314.15 Damp or Wet Locations.

In damp or wet locations, boxes, conduit bodies, and fittings shall be placed or equipped so as to prevent moisture from entering or accumulating within the box, conduit body, or fitting.

Boxes, conduit bodies, and fittings installed in wet locations shall be listed for use in wet locations.

Approved drainage openings not larger than 6 mm (1⁄4 in.) shall be permitted to be installed in the field in boxes or conduit bodies listed for use in damp or wet locations.

For installation of listed drain fittings, larger openings are permitted to be installed in the field in accordance with manufacturer’s instructions.

You can buy a copy or you can obtain free access to view the current 2020 NEC at NFPA at https://www.nfpa.org/ where you can view all of article 314.



There are bathroom or shower or tub lighting installation details required such as meeting an 8 ft. height over the shower floor (or tub rim) and more in NEC 410.10 (A) and (D).

US NEC 410.10 (A) Wet and Damp Locations

Luminaires installed in wet or damp locations shall be installed such that water cannot enter or accumulate in wiring compartments, lampholders, or other electrical parts.

All luminaires installed in wet locations shall be marked, "Suitable for Wet Locations." All luminaires installed in damp locations shall be marked "Suitable for Wet Locations" or "Suitable for Damp Locations."

and

US NEC 410.10 (D) Bathub and Shower Areas

A luminaire installed in a bathub or shower area shall meet all of the following requirements:

(1) No parts of cord-connected luminaires, chain-, cable-, or cord-suspended luminaires, lighting track, pendants, or ceiling suspended (paddle) fans shall be located within a zone measured 900 mm(3 ft) horizontally and 2.5 m (8 ft) vertically from the top of the bathub rim or shower stall threshold.

This zone is all-encompassing and includes the space directly over the tub or shower stall.

(2) Luminaires located within the actual outside dimension of the bathtub or shower to a height of 2.5m (8 ft.) vertically from the top of the bathtub rim or shower threshold shall be marked suitable for damp locations or marrked 'suitable fo wet locations."

Luminaires located where subject to shower spray shall be marked suitable for wet locations.



Let's look again at US NEC 410.10 (D) (1) more-closely: this prohibition is for types of lights (or certain fans) that are over the tub or shower and that involve cords, chains, pendants, hanging cords, etc.

Below is an example of a "legal" water-tight (LED in this case) ceiling light fixture (no fan, this bath vents via a window) that installed over a shower stall.

The light fixture was listed as "Suitable for Wet Locations" by the manufacturer, is UL listed, and has no exposed wiring, cords, switches, etc. and is sealed against water entry. (The electrical box and connections for this device are accessible from an attic over this area. )

On 2020-09-28 by Katalin - we heard from an electrician friend that we can’t put a fan in the shower are

Hello,
We live in Hudson-OH.
Planning to update our small master bathroom (approx 6 feet by 8 feet surface). It has a std. standing shower, tiny vanity and toilet bowl. It has a std size window.

Actually the fan is a separate unit and we have a shower overhead light. We would like to install a 2 in 1 overhead shower exhaust fan/light. Is it okay with the regulations to install this unit directly in the shower ceiling?

Aero Pure Quiet Adjustable 50-80-110 CFM White Energy Star Bathroom Exhaust Fan with LED Light/Nightlight 0.4 Sones - ETL listed for wet application when used with a GFCI branch circuit wire.

I am concerned because we heard from an electrician friend that we can’t put a fan in the shower area. Want to be 100% sure before proceeding.
Thanks!

On 2020-09-15 by (mod) - My bathroom vent is vented to my attic

Grandfathering won't eliminate the risks of mold contamination; the vent needs to be routed outside. I hope that the cost of that fix is trivial compared with the value of the home being sold; in my OPINION, if I were selling my home and the only issue were the one you cite, I'd leap to get it fixed and close the deal.

On 2020-09-14 by Joann

My house is 20 years old, built by Toll Brothers. My bathroom vent is vented to my attic. Obviously it passed inspection 20 years ago. I am no selling my house and I am being told this is not to code, it must be vented to the outside. I am trying to determine if I am grandfathered in since I have not done any structual changes to the bathroom, it is exactly how it was when I purchased it 15 years ago. Can you please tell me if I am grandfathered in?

 

On 2020-09-12 by (mod) - bathroom ceiling fan vents into concrete ceiling space

Brian,

Your vent needs to exhaust to the outdoors. [Photo above]

The reason the model building and ventilation codes specify that such vents need to be directed to the building exterior is that dumping moist air into a ceiling space or plenum is inviting a future mold contamination problem that can be both unsafe and expensive to cure.

On 2020-09-12 by Brian

I am on the the 3rd floor of a 3 story hollow core concrete condo. I have a concrete ceiling, and I have a sheetrock ceiling in my bathroom about a foot below the concrete ceiling.

There is a soffit that runs from my LR, around my kitchen and to my bath which houses the water pipes.

My bath fan vents to this space between the ceiling and sub ceiling and then into the soffit. Is this how it should be ?

On 2020-08-21 by Barry

my bathroom exhaust fan has vent line which is vertical exiting through the roof, Should the venting line be straight to the exit port or should there be a loop or dip in it to catch condensation from going back into the fan?

On 2020-07-06 - by (mod) -

Caryn

We give venting specs above on this page and in this article series.

Also,
The IO manual for your vent fan will tell us exactly what the manufacturer wants you to use - they're an even better source than the specs given here and in this article series, as they are an exact match for your fan.

On 2020-07-06 by Caryn

I live in San Diego, CA. I am adding two bathrooms exhaust fans in new construction. I need to know the required specifications for the ducting length and material. They are both currently 80 cfm. I am considering switching them out to a 110 cfm. Can you get me the specs for both sizes?
Thank you

On 2020-07-01 by (mod) - Bath exhaust vented to gutter: when we had a large rain storm, the water came pouring in through the vent

James

Good grief,

A nutty installation and wierd advice.

The wise lady from Philadelphia would say find a better contractor.

On 2020-06-30 by James

Hi,
Our contractor just put in a vent for our upstairs bathroom. When we had a large rain storm, the water came pouring in through the vent. I finally managed to figure out where it was vented to the outside.

It was opened right into our gutter!! I called the contractor, who just couldn't believe his group would do that.

Anyway, he has suggested fitting the current opening with an extended pipe that will go through the gutter (from one side to the other).

My concern is the pipe will take up too much space in the gutter, thus causing overflow of the gutter during heavy rains and the possibility of leaves or other debris getting stuck underneath the pipe and causing a back up in the gutter. Also, it doesn’t look cosmetically proper. My question is his fix suggestion even to code? Thanks in advance, James.

On 2020-05-15 - by (mod) -

Bathroom exhaust vent clearance above ground

Terry

Thanks for a question that bothers lots of people.

Bathroom exhaust vent clearance above ground:

The words "above ground" do not appear in the Chapter 15 - Exhaust Systems of the IRC. I'll give articles that include code citations below in this reply.

Instead in the IRC Chapter 15 we have more general:

IRC M1506.3 Exhaust Openings

Air exhaust openings shall terminate not less than 3 feet (914 mm) from property lines; 3 feet (914 mm) from operable and nonoperable openings into the building and 10 feet (3048 mm) from mechanical air intakes except where the opening is located 3 feet (914 mm) above the air intake. Openings shall comply with Sections R303.5.2 and R303.6.

R303.5.2 Exhaust Openings

Exhaust air shall not be directed onto walkways. All exhaust ducts shall terminate outside the building. Terminal elements shall have at least the equivalent net free area of the duct work.

R303.6 Outside Opening Protection [for air intake & exaust openings]

Air exhaust and intake openings that terminate outdoors shall be protected with corrosion-resistant screens, louvers or grilles having an opening size of not less than 1/4 inch (6 mm) and a maximum opening size of 1/2 inch (13 mm), in any dimension.

Openings shall be protected against local weather conditions.

Outdoor air exhaust and intake openings shall meet the provisions for exterior wall opening protectives in accordance with this code.

Please take a look at BATHROOM VENT DUCT TERMINATION

and

More specifications are at BATHROOM VENT CLEARANCES

Separately at CLOTHES DRYER VENTING

we discuss ground clearances that ARE given explicitly, probably because unlike a bath exhaust vent that, if blocked, may lead to odor or moisture problems, a blocked dryer exhaust vent can or at least in older dryer installations risked a building fire.

So I'm left with OPINON that 24" is a minimum and that you do not want your exhaust vent to be covered or blocked by accumulated snow (or anything else).

On 2020-05-15 by Terry

I have a bathroom below grade that we are remodeling. How high must the external facing exhaust cap be above the ground? We live in the northeast and get a fair amount of snow every year.

On 2020-03-18 by (mod) - North Carolina's 2012 mechanical code on exhaust ventilation

Rock

North Carolina's 2012 mechanical code gives lots of detail on exhaust ventilation but I don't see a specification of the exhaust duct material itself.

Note that exhaust duct specifications in the NC code will differ from specifications for heating or air conditioning ductwork.

On 2020-03-17 by Rocklin D

Are metal or rigid ducting required by code for bathroom exhausr fans in NC

On 2020-02-26 - by (mod) - Bath exhaust vents need to be directed to the outdoors - not just dumped anywhere inside the building

Anon

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.

On 2020-02-26 by Anonymous

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.

On 2020-02-25 - by (mod) - Bath exhaust vents need to be directed to the outdoors

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

On 2020-02-24 by Jeff

Is it okay to vent a ceiling fan into the attic for just a toilet room? What is the IRC code referencing this?

On 2020-02-19 - by (mod) -

Joe

The exhaust vent duct should not terminate in an attic or roof space; it needs to vent to the building exterior.

On 2020-02-19 by joe

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?

 

On 2020-01-31 - by (mod) - use 4"PVC pipe as an exhaust duct

Its ok if the length, slope, etc. are following the manufacturer's guidelines.

On 2020-01-30 by Curt G

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.
cjnsg@tds.net

On 2019-10-02 - by (mod) - maximum bath exhaust vent fan duct length

Joe,

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

On 2019-10-02 by Joe

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

On 2019-08-19 - by (mod) -

Matt

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.

On 2019-08-16 by Matt

Is there a requirement for seperation between ac/ heat registers and the exhaust fan housing

On 2019-08-18 - by (mod) - possible and up to code to put all your vents together "

Sarah:

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.

On 2019-08-15 by Sarah

Is it possible and up to code to put all you vents together so there is only one stack coming out of the roof

On 2019-08-16 by (mod) - requirement for seperation between ac/ heat registers and the exhaust fan housing?

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.

On 2019-08-16 by Matt

Is there a requirement for seperation between ac/ heat registers and the exhaust fan housing?

On 2019-08-18 by (mod) - cannot necessarily put all plumbing vents out through a roof at a single point

Sarah:

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.

On 2019-08-15 by Sarah

Is it possible and up to code to put all you vents together so there is only one stack coming out of the roof

On 2019-07-15 by (mod) - bad idea to step down the vent duct diameter

It's always a bad idea to step down the vent duct diameter. You will significantly reduce the air flow rate

On 2019-07-12 by Molly

I am installing a FV-11VHL2 bath fan which moves 110 CFM. For ducting, I would use rigid, smooth, metal ducting. I will have a 3 foot run before I make a 90 degree turn and go another 1.5 feet to exit home laterally.

Planning to slope 1/4 inch per foot toward the outside (live in CA, non freezing weather) But there is a tight spot under an eve where I will exit (I will extend past the eve as its against code to exit under an eve)

My question is, since the exit spot is tight, I was wondering if I could transition from a 4 inch vent diameter to a 3 inch diameter before exiting the home. Is this ok or would it be a very bad idea? Anyone know CA codes because I am not sure if there is a minimum diameter required for this.
. Thanks for help.

On 2019-05-31 by Dan Want to install exhaust fan vent with light and night light.inside tub.

Want to install exhaust fan vent with light and night light.inside tub.
How to wire gfic to vent and switch?

Thank you!

On 2019-02-23 by (mod) - reddish liquid dripping back in through the bathroom vent fan in the second floor bathrooms

Michael

I suspect that either there are ice dam leaks in your roof
or condensate inside the fan duct is dissolving debirs and leaking back
through the fan.

Take a look in the attic above the bath and let us know what you see.

On 2019-02-23 by Michael

Hi we are having reddish liquid dripping back in through the bathroom vent fan in the second floor bathrooms. We mainly get it after a significant snowfall and when the weather warms and the snow begins to melt from the roof.

This was the amount from two bathroom fans over a 6 hour period where it dripped consistently. We got the same amount again today when we arrived home. No other condensation or dripping occurs during a shower or bath. We are extremely frustrated and people we've paid to fix it haven't and no one will help. I just came across your website and thought I'd give it a shot. Thanks for your help.

IMAGE LOST by older version of Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2018-11-28 by (mod) -

Sure Jack,

Please see BATHROOM VENT OUT THROUGH SOFFIT at https://inspectapedia.com/ventilation/Bathroom-Vent-Through-Soffit.php

take a look at the discussion, illustrations, and also the soffit vent termination kit instructions we provide there from the major manufacturers.

Then help me out by asking for more information or offering a critique about what's unclear or missing.

Thanks.

On 2018-11-28 by Jack

Can you direct me to a detail of a properly vented bathroom fan thru a soffit?

On 2018-11-18 by (mod) - odors from the apartment below mine

Stench

Perhaps a combination of fresh air inlet supply and finding and sealing air leaks in from your neighbors will help

On 2018-11-18 by SecondStoryStench

When I turn on my bathroom exhaust fan in the bathroom of my apartment odors from the apartment below mine come up from the floor in the little alcove immediately outside the bathroom door. Tge apartment is carpeted.

Even when my fan is off I'll get odors from adjacent apartments. I should just move. Right? I mean, the whole ventilation system probably needs to be replaced and installed properly. That's my guess.

On 2018-11-18 by (mod) - odors from the apartment below mine come up from the floor

Stench

Perhaps a combination of fresh air inlet supply and finding and sealing air leaks in from your neighbors will help

On 2018-11-18 by SecondStoryStench

When I turn on my bathroom exhaust fan in the bathroom of my apartment odors from the apartment below mine come up from the floor in the little alcove immediately outside the bathroom door.

The apartment is carpeted. Even when my fan is off I'll get odors from adjacent apartments. I should just move. Right? I mean, the whole ventilation system probably needs to be replaced and installed properly. That's my guess.

On 2018-09-09 by (mod) - Never should a bathroom fan terminate by simply blowing into the attic.

Never should a bathroom fan terminate by simply blowing into the attic. You're inviting a moisture and mold problem. The fan should be ducted to the exterior of the building. You should see that in just about every building code.

On 2018-09-04 by ronald.zielinski@sbcglobal.net

Question: do bathroom fans have to ventilate outside through roof or soffit or just up into the attic according to St Joseph County, Indiana code.

On 2018-08-31 by (mod) - Can bathroom exhaust fan share the vent from a drier to exit roof?

No.

See BATH KITCHEN VENT DUCT SHARING for details or read my summary and citations just below.

Your vent duct sharing proposal is a bad idea in my view for several reasons including

- violation of building codes for both types of vents; clothes dryer vents must be independent of other vent systems

See CLOTHES DRYER VENT CLEARANCES & TERMINATION https://inspectapedia.com/Appliances/Clothes_Dryer_Vent_Clearances.php

and for code examples see

New Jersey Mechanical Code Chapter 5 EXHAUST STSTEMS [PDF] (2006), https://inspectapedia.com/ventilation/NYC-Chapter-%205-Exhaust-System-Codepdf.pdf

Excerpt:

504.1 Installation [of clothes dryer exhaust vents]

Clothes dryers shall be exhausted in accordance with the manufacturer's instructions. Dryer exhaust systems shall be independent of all other systems and shall convey the moisture and any products of combustion to the outside of the building.

- inadequate capacity

- condensate drain-back into the bath or into the dryer bottom

- fire spread hazards

- violation of instructions provided by the manufacturers of both appliances

- possibly the vent distance is too long, raising a fire hazard at the dryer

Some dryer manufacturers permit installations with dryer exhaust venting of much greater lengths [though perhaps combined with a requirement to avoid use of 90 degree turns in the duct system]

Note: Fantech notes that "The 2012 International Residential Code (IRC) is pretty specific when it comes to dryer exhaust venting.

The maximum length for dryer exhaust duct cannot exceed 35 feet from the dryer location to the wall or roof termination. " (Fantech 2012)

IBC / ICC Code: Clothes dryer exhaust, Section 504.4

On 2018-08-31 by Larry Brown

Can bathroom exhaust fan share the vent from a drier to exit roof?

On 2018-07-25 by (mod) - galvanize steel snap-together exhaust duct

In our own installation(s) I like to use galvanize steel snap-together duct like the one shown below. That's 26-gauge.

The material is sold in various diameter, 4" is shown.

If you need more-durable heavier gauge or longer runs the same product is sold in 30-gauge (and also in very common 24-gauge).

On 2018-07-25 14:37:02.053477 by Kevin

What gauge solid metal duct do you recommend for bathroom fan ventilation ?

On 2018-07-21 13:20:24.857035 by (mod) -

If it were my project I'd take the short route, figuring that overall it'll be more-reliable and less-expensive.

If you connect a vent to a drain take care for proper air gaps, avoiding back drafts, sewer gas hazards, bacterial hazards etc.

On 2018-07-21 02:42:04.582127 by Scott

Thanks Dan. I was anticipating using pvc piping which wouldn’t be an issue with being wet. And also easy to install a tee at the low point. Thinking 1/2” routed down to the drain. I will check some fan specs to see if it can push air that far

. A booster may be necessary....and if that doesn’t work, I do have another direction to run. Much shorter (less than 10’) but I would need to remove a section o my front porch and it would be vented out the side wall under the porch. Probably not ideal for anyone sitting there when the fan runs.

On 2018-07-20 by (mod) - too-long exhaust vent duct runs mean trouble

Scott

I see trouble just as do you

The length of your run is excessive even without the two 90 degree elbows, resulting in inadequate fan performance.

The solutions, that you would review with your fan manufacturer probably involve a larger duct and/or some booster fans.

A low spot in bath exhaust fan ducting will collect water just as you anticipate. Installing a drain may solve the blockage problem but I'm not sure that your duct material is designed to be constantly wet. Perhaps you'll put your exhaust booster past that point.

On 2018-07-20 by Scott

I am installing a new basement bathroom that will not have a window.

The routing for the exhaust fan duct I want to use is about 50 feet long with two 90s in it. Due to the length of the run and layout of the joists, I am struggling with sloping it to the outside. I am wondering if I can slope it in two directions.

From the fan downward and then back up again towards the outside. This will create a low point, but it will be in the mechanical room of the basement.

I can install a low point drain to a floor drain. Is this acceptable? Will it work?

On 2018-06-14 01:08:07.472812 by (mod) -

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.

On 2018-06-13 13:59:12.145495 by Crescent

What cfm should be of a bàthroom fan in a town house

On 2018-06-01 15:07:05.745135 by (mod) -

Simply put, NO. You cannot (by code) and should not (by practical reasoning) share exhaust venting between a kitchen exhaust and a bathroom exhaust fan.

The design requirements and materials are different between bath exhaust vent systems and kitchen exhaust vent systems, and such sharing is prohibited by the model mechanical codes and shared ducting are likely to be prohibited by local building codes and code inspectors.

Authority: 2015 International Mechanical Code, Section 505, Domestic Kitchen Exhaust Equipment, 505.1, excerpt: Such ducts shall have smooth inner walls, shall be air tight, shall be equipped with a backdraft damper, and shall be independent of all other exhaust systems. - https://www.up.codes/viewer/utah/imc-2015/chapter/5/exhaust-systems#505.1

I will add details and more code citations here and in our article KITCHEN VENTILATION DESIGN at https://inspectapedia.com/BestPractices/Kitchen_Vent_Fan_Specifications.php

Also see VENTILATION CODES - https://inspectapedia.com/Design/COPIES-of-BUILDING-CODES.php#Ventilation

On 2018-06-01 12:08:31.436982 by John

Can the bath fan and kitchen fan use the same exhaust pipe through the roof?

On 2018-05-26 00:42:58.162795 by (mod) -

That is an interesting opinion, Newbie. Thank you for the comment.

I have not come across a claim in any scholarly or building research that supports the hypothesis that venting out of the soffit fouls attic ventilation.

The vent, when it's running, blows air out and down away from the structure sufficiently that in my OPINION there's no risk of a backdraft of wet or moist air into the attic.

Certainly while it's not scholarly research, in the inspection of several thousand buildings over 40 years, where I have found soffit exit vents I have not once seen evidence of condensation or moisture blowback from the vent's exit.

There are, of course, critical design points for attic venting to work, including ridge outlet and soffit intake venting.

Details are at ROOF VENTILATION SPECIFICATIONS https://inspectapedia.com/ventilation/Roof_Ventilation_Specs.php

Where I have found bath vents that caused trouble in the attic, and I have certainly seen that, it has not been from moisture backdrafting into the attic from the soffit.

Rather it has been where the vent is not properly installed, such as venting directly into the attic - a very bad idea, or improper duct routing (sags, too long, too many bends), or duct damage and leaks - any of which can dump moist bathroom air into the attic.

We see related building problems with side-wall vents if the vent is leaky or improperlhy installed, though there the moisture may blow into the wall cavity rather than the attic.

If you have photos or links to photos showing the problems you describe I would very much like to see those and thus to do further research.

On 2018-05-26 00:33:52.484297 by NewHomeGuy

The one part about all of this that concerns me: I have read so many articles saying that hooking a vent to a soffit is highly undesirable because, at least where I am from, those are designed to take air into an attic and keep it ventilated and, in the winter, cool. They say the risk of humid, hot air entering the attic with this setup is too great. I've even seen photos of mold forming around bathroom vents that exit through a soffit.

On 2018-04-24 15:57:45.211112 by (mod) - How far away does a bath fan exhaust have to be from the furthest open point on a window.

Jordan

Please see

BATHROOM VENT CLEARANCES

On 2018-04-19 by Jordan

How far away does a bath fan exhaust have to be from the furthest open point on a window.

On 2013-04-01 by (mod) - recirculating bath vent air?

I'm not sure what you mean by "recirculating" replacement. We don't want to recirculate bath air we want to vent it out.

Expensive; maybe possibly reasonable if the vents are run for a long time every day.

About tying a bath vent and dryer vent together - I worry you're asking for back-venting when the dryer is running; I don't see these vents in common.

Doing so is unsafe and violates building codes.

See BATH KITCHEN VENT DUCT SHARING

Perhaps you are asking about an air-to-air heat exchanger type ventilator that preserves building heat while venting exhaust outdoors?

See VENTILATION, BALANCED

On 2013-03-31 by wendy

Our existing bathroom fan is a recirculating fan (with no dryer or air conditioner). It was an in-wall unit 5"w x 12"h and only 4"d (stud width).

This fan is in both of our first floor, condo bathrooms which have no windows.

We had assumed they were just old and inefficient, but now we understand why the ventilation in our bathroom is so terrible. I have been unable to locate a recirculating replacement - though am not sure that would suffice for current building codes anyway

So all that said, we have very limited options but must have something. To run venting to the exterior, would be challenging (and expensive) since we would be modifying the exterior of the building - monitored by the HOA. The only exterior venting we have is for our in-unit dryer venting.

Can we tie into that venting? My intuition says no, but I can't find any confirmation online.

This fan is in both of our first floor, condo bathrooms which have no windows. We had assumed they were just old and inefficient, but now we understand why the ventilation in our bathroom is so terrible.

I have been unable to locate a recirculating replacement - though am not sure that would suffice for current building codes anyway. So all that said, we have very limited options but must have something.

To run venting to the exterior, would be challenging (and expensive) since we would be modifying the exterior of the building - monitored by the HOA.

The only exterior venting we have is for our in-unit dryer venting. Can we tie into that venting? My intuition says no, but I can't find any confirmation online.

On 2013-03-30 by (mod) - Landlord hooked up the bathroom vent to the stove exhaust vent

Watch out: Jason I'm nervous about offering anything diagnostic when I'm unclear on EXACTLY what's installed, but certainly if there are bath vents connected to a vent designed to exhaust from a kitchen stove I'm afraid there may be a serious fire hazard. (and be a code violation)

If we simply have too many bath vents tied together with too-long runs and too much flex-duct, then the bath vents are not going to ventilate successfully, risking high bath moisture and perhaps mold growth.

If you are convinced there are unsafe conditions in the home first ask the landlord to have someone competent take a look - ask in writing.

If there is no response you might have to ask your building department or health department for help. I'd be sure to try working with the landlord first.

On 2013-03-29 by jason h.

my landlord just had my bathroom remodeled, everything was going ok until he asked to go into the attic.

After he was done i went up there to see what he was doing there is 4 air vent for the attic and one piece of pipe that goes through the roof upon looking i noticed that he has hooked up the bathroom vent and the vent above the stove to it,

the vent above the stove is dryer hose and runs at an angle towards the vent withch is about 25 to 30 feet and the bathroon vents run at an angle to but the distance is about 15 feet and the apartment next door also is hooked up the same way all 4 of these vent run into this 1 exaust pipe,

what kind of hazards can this cause, i need to know because my wife is allergic to mold and get really sick when she come's in contact or inhales it also. Who can i contact about this.

On 2013-03-03 by John

Our house was built in 1992 and I have installed 2 new Nutone 50cmf fans in our 2 baths.

I replaced all the white 3" duct with 4" silver duct. And was wondering since both fans were routed to a single roof vent, Is it ok to do the same into a 5" T piece of duct?

The old 3"ers were just stuffed into a 4.5" hole in the roof & not very well I might add. I don't want to run into a situation where i have to re-do this later. I'm planning on insulating the flexible duct too to cut down on any issues with water accumulation. Thanks

On 2013-02-20 by Mike

I have to install a new bath fan because the old one finally gave out.

The new fan I got has the vent connection kind of offset from where the old one was and of course the rigid duct will not bend over about 3 inches to connect up.

My thought is that I can just cut the rigid vent back about a foot and use flexible duct to connect things up nicely, however is this a concern since moisture can build up and everything?

Seems like if I try to keep bends to an absolute minimum I should be okay but just wanted to check to see if there is maybe a better way to do this. Not sure that a rigid 90 degree elbow will work but that would be my first choice. Thoughts?

On 2013-01-18 19:12:57.421250 by Theresa Hunt

We had a new roof installed in the summer with the ridge vents now we are having problems with the bathroom fan leaking water, the roofer said it is due to water icing in the pipe leading to the vent then melting when the shower is run, does this mean its been installed wrong, he said there is nothing he can do but I can imagine all houses with the vent ridge having this problem.

On 2013-01-16 02:49:13.927507 by H. J.

How to clean dust from a Nutone bath vent/fan.
Thanks.

On 2013-01-10 13:01:14.326196 by PB

We are needing to vent a bathroom ina grade 2 listed building with no soffit. we can't alter the roof or the walls. Any suggestions?

On 2012-12-06 00:17:41.941484 by Doug from Portland, OR

Is there any code relationship of bathroom volume to required ventilation CFM? The new 62.2-2010 recommendations seems to just specify a prescriptive 50 cfm minimum intermittent by virtue of the fact that the room is a "bathroom."

On 2012-10-31 21:21:45.926768 by Anonymous

We are using the foam insulation in our new home that is applied in all exterior walls and at the under part of the roof making it like an igloo. What is the best way to install bathroom vents as not to have cold air pouring into the attic through the ducts

On 2012-10-31 15:44:37.728599 by Sam

Please bear with me, as this may be a silly question. I am attempting to replace an existing fan, but I'm having difficulty finding a new fan that works in alignment with where the current ductwork is. How, or where, do I find a fan to fit where the previous equipment could connect to the ductwork? It is a 1st floor bathroom, and there are some pipes in the way of moving the ductwork to a different location. Unfortunately I'm not able to find the previous fan. Do most manufacturers make various models to accommodate these scenarios? Maybe I just haven't looked hard enough. Please help!!

On 2012-10-28 19:05:40.620317 by V99

I live in a 3story Victorian apartment that has a verticle airshaft with. I am on the 3rd floor, in the bathroom there is a large rectangular 'window' opens inward (hinges on the bottom).

This 'window' leads to the verticle air shaft. Is it possible to have this window replaced with an extractor fan, so that when I shower the fan removes the humidity into the verticle airshaft?

On 2012-07-29 02:22:06.642531 by (mod) -

Hugh, I bet if you discuss this backwards hot air flow with your plumbing supplier they can suggest an automatic vent damper that closes the kitchen fan vent when it's not in use.

On 2012-07-23 17:20:30.400406 by Hugh

I do not have air conditioning in my house, and I just noticed that above my kitchen exhaust, hot air from the attic is spilling into the house.

I have cut foam board and sealed behind the duct, and I have sprayed foam around the sides of the duct going into the attic.

Since the duct is metal, and is exposed to the sun during the day, I can feel the absorbed heat (from the roof vent) on the duct, in the kitchen cabinet above the exhaust. Do you suggestion for a type of insulation to wrap around the duct, and should I wrap the duct in the attic and/or the kitchen cabinet?

On 2012-07-11 19:48:28.169438 by Andrea Pumphrey

We are remodeling our bathroom and the existing fan vents into the attic. When we install the new fan, is it okay to vent it by running the ducting from the new fan to join with the ducting from the other bathroom's ducting which does vent to the outside.?

The new fan is about 5 feet away from the fan in our other upstair's bathroom (the bathrooms share a common wall, one is an ensuite, one is the main bath). Would these cause problems with one fan pushing moisture into the other bathroom, instead of outside?

On 2012-07-09 16:23:34.125751 by DANNY B.

1/2 BATHS WITH NO WINDOW, DOES THE SEPERATE LIGHT AND SEPERATE VENT BY CODE NEED TO BE ON 1 SWITCH OR CAN YOU HAVE 2 SEPERATE SWITCHES, AND WHAT IS THE CODE SECTION?

On 2012-06-24 11:39:44.069637 by Don P.

Great advice all! A great site I'm adding to my favorites!!

On 2012-03-29 11:33:18.350000 by Peeter

Please specify: should slope the bath fan vent duct downwards towards its building exit or gently back towards the bathroom?

On 2012-02-18 05:45:34.085020 by Chis

Can You install a vent above the bathtub near the shower?

On 2012-01-22 09:49:52.981107 by Anonymous

my ceiling mounted bathroom extractor fan has started to make a loud noise when it is in operation. I have taken a look in the loft and cleaned the non return 'valve' flap as it was quite dusty. This seem to do the trick for a while but alas the noise has come back even louder? Is it the motor? Do you think I need a new fan and if so does one size fit all as the vent in the ceiling doesnt have to be take off as the current fan sits on top of it albeit from the loft side. Any tips? Pete

On 2012-01-22 04:59:26.300628 by Height of basement bathroom vent

If I install a basement bathroom fan, I estimate that the vent cover outside will be at most one feet to one and a half feet above ground level without going through the floor. I am concerned about bugs, termites or rodents as it's only 1-1.5 feet above ground level. Is the distance an issue? What can I do to address it? Are there any recommended vent covers which will address this? Thanks.

On 2012-01-21 18:14:36.111255 by Ben

Anonymous, you're right there was a leak in the duct but I fixed it with foil tape and I am using 4" metal duct. The route I have to the outside is kind of long for how small my house is (15' run approx.) I originally didn't want to run it out the roof but now I think that may have been th better option. I am getting a new roof in the spring so I may change how the duct is run at that point.

The biggest problem seems to be the steam coming around the vent housing, I currently have plumbers putty filling the gap between th housing and the drywall but was looking for a more correct fix to the problem. The amount of steam coming around the vent actually increases when the vent is shut off (keep in mind I'm doing these tests while the hot shower is running so I can see th steam)

On 2012-01-21 18:03:08.386835 by Anonymous

Ben,

It sounds as if your bathroom vent fan duct connection is leaky or perhaps the flex duct was torn. When you get over the vent fan and duct in the attic as you will need to do to insulate the duct, make sure that

- the duct is undamaged and is secured to the vent fan

- that there are not other leaks out of the fan housing - foil tape can help seal openings if needed

- that the ducting has no low points that will collect condensate

- that the duct has a straight as possible, short as possible path to outdoors.

Consider changing the ducting to solid 4" metal for better airflow

On 2012-01-21 17:53:28.825006 by Ben

Having a problem with ice forming in my attic. My bathroom vent ducts are not insulated so I will fix that but I noticed there is a lot of steam coming into the attic around the vent itself and is also leaking out of the vent itself. The whole in th drywall around the vent isn't very big, small enough that I'm thinking about caulking it shut.

Do you have better advice on how to fix that? Really appreciate your help.

On 2012-01-11 00:49:35.559331 by Ian

Is there a minimum distance between a building-side vent and a window?

On 2012-01-03 23:47:22.584212 by (mod) -

Mary,

It is possible to route a bath vent fan down, horiztontally through the crawl space, then outside, but I'd be careful to pitch the vent so that it will drain to outdoors and not otherwise collect water. But you may find that the length and direction of run of ducting for the fan will require a more powerful vent fan.

Also I'd recommend use of galvanized metal ducting rather than flex-duct in order to make airflow as easy and effective as possible.

On 2012-01-03 19:46:14.515332 by mary

Can a 1st floor powder room be vented down thru a crawl space then out thru a side wall??

...

Continue reading at BATHROOM VENTILATION DESIGN Best-Practices, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Building Ventilation Articles

• BATHROOM VENTILATION CODES SPECS - home
• BATHROOM VENTILATION DESIGN
• BATHROOM FAN ENERGY COST
• BATHROOM FAN HEAT RECOVERY
• BATHROOM FAN WIRING
• BATH KITCHEN VENT DUCT SHARING
• BATHROOM VENT AIR FLOW MEASUREMENT
• BATHROOM VENT AIR SUPPLY
• BATHROOM VENT CLEARANCES
• BATHROOM VENT CODES
• BATHROOM VENT DUCT LENGTHS
• BATHROOM VENT DUCT MATERIALS
• BATHROOM VENT DUCT ROUTING
• BATHROOM VENT DUCT INSULATION
• BATHROOM VENT DUCT SLOPE
• BATHROOM VENT DUCT TERMINATION
• BATHROOM VENT DUCT PROTECTION
• BATHROOM VENT FAN SIZING & NOISE RATINGS
• BATHROOM VENT DOWN in CATHEDRAL CEILING
• BATHROOM VENT DOWN THROUGH FLOOR / CRAWL AREA
• BATHROOM VENT UP THROUGH ROOF
• BUILDING CODE DOWNLOADS - free downloadable PDF files of building codes & standards
• FAN ENERGY INDEX FEI
• FAN NOISES in BUILDINGS
• HUMIDITY LEVEL TARGET
• ODORS GASES SMELLS, DIAGNOSIS & CURE - home
• PRYNE VENTILATION FANS CATALOG 1950 [PDF]
• TRADEWIND KITCHEN VENT CATALOG 1950 [PDF]
• VENTILATION in BUILDINGS - home

Suggested citation for this web page

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

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INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING VENTILATION

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