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Bathroom ventilation: Fact and fiction

Bathroom fan replacement across Canada could almost become an industry in itself. Vast numbers of them aren't doing what they were designed to do.


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December 11, 2012 by Steve Payne

By Glenn Curtis

Is that bathroom fan really doing what it was designed to do? Research performed by the CMHC (Canada Mortgage and Housing Corporation) has found that many homes have bathroom exhaust fans that are noisy, move very little air and are not energy efficient.  Many homeowners are not even aware that their current bathroom fans may be contributing to damage in their homes.

Bathroom exhaust fans are an important part of a home’s ventilation system. They eliminate odors, improve indoor air quality, and remove moisture and humidity that can lead to structural damage or mildew and mold growth. Unless a bathroom is properly ventilated, the moisture from a shower has no place to go and can penetrate into drywall, attic insulation and structural joists. If a mirror is steamed after a shower, or there is a build-up of condensation on bathroom walls, it may be time to service or upgrade the bathroom fan.

CHMC’s research shows that many bathroom fans across Canada should be replaced or serviced due to inadequate airflow, inability to overcome static pressure, high leakage rates and generally poor condition. Inadequate airflow was cited as the most common problem, with improper fan selection being among the causes.

There are several factors to be considered when selecting a new or replacement bathroom fan: airflow rate, sound levels, energy efficiency, and aesthetics and fan control.

 

Airflow rate

Of the factors listed above, the airflow rate is the most important. The Home Ventilating Institute (HVI) has provided guidelines for the proper ventilation of a bathroom. For bathrooms under 100 square feet, the basic rule is to exhaust a minimum of one cfm (cubic foot per minute) for every square foot of bathroom area. So an 8’ x 10’ bathroom, 80 square feet, would have a minimum airflow requirement of 80 cfm. For bathrooms over 100 square feet, the calculations are based not on square footage, but on the number and type of fixtures in the bathroom. An allowance of 50 cfm should be made for each standard toilet, bathtub and shower. Allow 100 cfm for whirlpools and hot tubs. For example, a bathroom with a hot tub, shower stall and toilet would require a minimum of 200 cfm (100 + 50 + 50).

Once the required airflow in cfm has been determined, it is necessary to establish the amount of static pressure (SP), or resistance to airflow, in the exhaust duct system. This has a significant influence on the amount of airflow the fan will deliver.  Many bathroom exhaust systems have a static pressure of 0.3” to 0.5”, which must be taken into consideration when selecting a bathroom fan.  When static pressure increases in an exhaust system, the amount of airflow, or cfm, decreases.

Most bathroom fans sold today are marketed with cfm levels based on open-air conditions, or 0” SP.  A fan rated for 100 cfm at 0” SP may not provide the necessary airflow for a bathroom when it is installed, because of high system resistance.  It has been determined that some bathroom fans with an initial rating of 90 cfm at 0” SP provide no airflow at all when installed in a typical bathroom exhaust system having 0.5” of static pressure. To avoid this problem, it is important to know manufacturers’ published airflow rates at varying static pressures to allow for proper fan selection.

Air make up is an important factor to consider when sizing a bathroom fan. Fans will only remove air from an area at the rate that the air can be replenished, regardless of the correct sizing or rated air flow. In many cases, the space between the bottom of the door and the floor is adequate, but in some cases an additional air make-up source must be installed to allow the fan to operate at peak performance, such as an additional grille installed in the bathroom door.

 

Sound level

The second issue is the sound level of the bathroom fan. Various studies have shown that many people do not turn on their bathroom fans because they are too noisy. If the fans do not operate, they serve no useful purpose. When considering fan sound levels, it is important to check for the HVI rating. If a bathroom fan does not carry an HVI rating, there is a very good chance that the fan will be noisy. Recently there have been several proposed changes to local codes indicating that a bathroom fan installed should not have a sound rating higher than 1.5 sones (a sone is a scientific unit of perceived loudness).

A quiet alternative to traditional bathroom fans is the remote mounted in-line ventilation fan. These fans are mounted in the attic, thereby removing the motor and fan assembly from within the bathroom itself, and provide quiet and effective exhaust ventilation to deal with most airflow requirements. By removing the fan assembly from the bathroom space and mounting it remotely, the possibility of the ultimate in quiet operation, virtually 0 sones, can be achieved (depending on how far away the fan is mounted).

 

Energy efficiency

With energy savings being on everyone’s mind, choosing an Energy Star fan is, without question, the best choice. More than half of the fans operating in Canada today are not energy efficient models; in fact, some fans in operation today are using more than 180 watts of power. A retrofit of the bathroom fan can lead to savings in the electrical bill and increased performance of the bathroom fan.

Aesthetics

Once a fan has been found that is quiet, energy efficient and delivers the required airflow, it is important to look at the esthetics of the fan, or how the fan will fit into the décor of the bathroom.  This is strictly a personal choice.  Two different styles of bathroom fans are worth considering: traditional ceiling mounted fans and remote mounted in-line fans.

Traditional ceiling mounted fans are most commonly seen in bathrooms today.  This type of fan has a fan and motor assembly mounted in the ceiling, housed in a box with a fixed air intake grille covering the mechanics of the fan.  Although many of the newer designs have improved sound levels and airflow rates, they still have the motor and fan assembly mounted in the bathroom area, tend to be noisy, and are not designed to overcome the higher static pressures found in many exhaust systems.

Remote mounted in-line ventilation fans provide a much quieter operation, and are designed to overcome higher static pressures typically found in bathroom exhaust systems.  In-line bathroom fans are normally mounted in the attic space, removing the mechanical aspects of the fan from the bathroom.  The only visible portion of the exhaust system in the bathroom is an attractive exhaust grille.  This provides a more esthetically pleasing look to the bathroom, with the ability to adjust airflow as required.

Another feature of remote mounted fans is that the air intake grille can be mounted directly over a shower or hot tub.  In addition, the ability exists for one fan to exhaust air through multiple grilles.  Remote mounted fans can provide up to 80% of initial fan rating, even with 0.5” of static pressure present in an exhaust system.  This may result in the reduction in the size of fan required to meet airflow requirements.

Fan control

The last point to consider when upgrading a bathroom ventilation system is how to control the fan.  This is an important aspect of the ventilation process, and is something that should be strongly considered.  CMHC and HVI both suggest that a bathroom fan run for a minimum of 20 minutes after a shower, to allow for the removal of excess humidity and moisture.  Many bathroom installations have the fan controlled by the same switch as the light, resulting in the fan being turned off as soon as the occupant leaves the room.  It is recommended that a separate switch control the fan or, better yet, a timer that allows the fan to run for a pre-determined amount of time after showering.

There are many aspects to properly selecting the correct bathroom exhaust fan.  Much of the information available today can be confusing.  Whatever choice is made, it is important that the selection is based on fact, and not fiction.

Glenn Curtis is the National Sales Manager at Soler & Palau and a member of HRAI’s IAQ Sector Council


Steve Payne

Steve Payne

Steve Payne is the editor of Canadian Contractor magazine
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49 Comments » for Bathroom ventilation: Fact and fiction
  1. Patrick Dugal says:

    I live in a row of condos that are 25 years old. It has come to my attention that the bathroom exhaust fan exhausts into the attic and not to the outdoors. Is this against the building code taking into when the condos were built? Thanks.

    P. Dugal

    • R. Corning says:

      Hi This practice was brought on and encouraged by poor quality builders (forcing subs to cut corners or saying they would put in vent line)off the fan.
      It was never an approved work procedure although the Inspection department was never much on due diligence.

  2. Glenn Curtis says:

    Patrick,

    I am not sure exactly when the code came into place, but in the Ontario Building Code Act 1992, Section 9.32.3.10.2 it clearly states that “Exhaust ducts shall not discharge into heated or unheated enclosed spaces.”. I know that this is also been in place for many years in other jurisdictions throughout Canada through the BC Building Code, Alberta Building Code and the National Building Code.

    With an exhaust fan terminating inside the attic, and not outdoors, there is a potential for the moisture and humidity to gather in the wood and insulation which can lead to mold, mildew and even structural damages to the wooden trusses and drywall ceilings.

    This needs to be addressed as soon as possible, and you may even consider having an assessment done to see if there is any mold issues in the attic or insulation.

    I hope that this information is of help to you. If you need to trace the codes back, I believe that most libraries will have copies of the local Building Codes where you can review the requirements – Section 9 deals with ventilation.

    G. Curtis

  3. Peter Dale says:

    Is there a formula or method for calculating the resistance to airflow (static pressure) in duct work? And can kitchen exhaust hood fans be tied into bathroom fan ductwork? Thanks.

    Peter Dale

  4. Glenn Curtis says:

    Peter,

    I will answer the 2nd question first – No.
    Local codes require that all kitchen hood exhaust be vented directly outside.
    Another inherent problem is that if either of the 2 fans (bathroom or range hood) is off, there is the possibility that the air you are trying to exhaust outside may actually end up in the other room.

    With regards to the calculations of the static pressure, it depends on how accurate you need to be. The actual calculation for round duct loss is as follows:

    Δp = (0.109136 q1.9) / de5.02
    where:
    Δp = friction (head or pressure loss) (inches water gauge/100 ft of duct)
    de = equivalent duct diameter (inches)
    q = air volume flow – (cfm – cubic feet per minute)

    For rectangular ducts the equivalent diameter must be calculated.

    If you do not have to be exact, you can find web based calculators that can be used to get an estimated static pressure loss.

  5. Randy says:

    Thanks for this article and the follow up posts. I wonder if anyone could provide further comments (or maybe a pointer to additional articles here) that talk about the bath fan ductwork / insulation aspects? In particular, I’m wondering if the insulation sleeves or “socks” sold in the box stores have adequate R value? I’m considering using these over 4″ ducts in the attic for ease of installation – but we have some cold Ontario winters here (this year especially). I believe these products offer something in the R4 to R6 range. I could probably do better with a home-grown approach to wrapping the ducts, but not sure if I need to go to that much trouble. Are better quality (high R value) duct insulation sleeves out there? Thanks for any advice….

  6. Stan Pasternak says:

    Live in a condo with 2 baths and two exhaust fans. I have a quote from a contractor to replace the motor and fan in the first and the fan in the second for $550.00. Is this within reason?

  7. Rob McIntosh says:

    I just purchased a new home in manitoba. The bathroom exhaust fans in two of the bathrooms appear to have little to no air flow. I tested this via a single ply of toilet paper and a puff of baby powder.

    Is there anything in the building code that states how many CFM ventilation fans for new construction need to have? Im trying to gather as much information as possible to go back to the builder with.

  8. john says:

    I keep hearing that there is a “code” requirement for a (3-way) switch controlling a bathroom fan outside the bathroom as well as one inside the bathroom. I can find no reference to this in either the building code or the electrical code. Can anyone enlighten me?

  9. carmen essex says:

    I would like to know, when venting a bathroom exhaust fan should it be vented up through roof. Getting different oppinions. Some say yes some say it should be vented to facia. I live in Ontario so does snow on roof change things.

  10. Glenn Curtis says:

    John,
    It depends on where you live. In Ontario, the code calls for the principal exhaust fan in the house to be hooked up to a 3-way switch, with one mounted near the thermostat of the home. This is designed as a way for the home owner to manually control the bathroom fan to help exchange the air in the home to promote better indoor air quality. Many of the newer homes are providing an HRV unit in the homes to accomplish this feat, removing the need for the additional switch. If you are looking into the codes, check the code referring to the “principal exhaust fan”.

    Carmen,
    It is really a matter of choice as to where the bathroom fan is vented to the outside, as long as it exhausts directly outside. The good majority of bathroom fans are vented through the roof, while some people are choosing to soffit vent them as an alternate. There is no definitive answer in the codes that pertain to where the air must vent out of the house. One thing to keep in mind though if choosing to soffit vent the fans, especially in Ontario, is that you are exhausting warm, moist air from the bathroom. In the middle of winter, this can create a situation where the exhaust point may become frozen and create a blockage.

    • Carmen Essex says:

      Thank you for that information, When venting through the roof should anything be done as to avoid chance of leaks. Also could snow build up be an issue.

    • Russell says:

      The individuals responsible for creating the Ont building code should reconsider the requirement for the 3-way controlled bath fan. The idea of the homeowner somehow detecting that the indoor air quality is poor and turning on the ventilation/primary path fan to improve the air quality is pretty silly. It gets used about as often as GFCI outlets are tested…..but that’s another thread..

  11. john says:

    Glenn – thanks for the clarification. It had occurred to me that might be the explanation, but deeming a puny bathroom fan to be the principal exhaust fan for a building seems like quite a stretch. I most cases the kitchen fan would be stronger, but neither should count as whole house ventilation – IMHO.

  12. marg says:

    I have just had my apt bathroom, torn apart for high level mold ( they wont tell me how high), I have an exhaust fan with what appears to be a birds nest…Does this need to be working according to the Code…I have no window in bathroom.

    Thank you

  13. Ruth says:

    We live in Alberta and our house has 2 bathrooms. one bath has a shower only and the vent goes straight through the roof for that bathroom. The second bath has a tub and shower however this bath has not been used for showering. The problem is that during the winter when the weather turns from very cold to warmer as happens in our area the fans drip water. The fan in the shower only bath is not a huge problem as it drips into the shower however the main bathroom is vented by a pipe leading to the other vent so only one vent goes thru the roof. Is this up to standard code for installing bathroom vents? Both pipes are wrapped with insulation.

  14. Tony says:

    Hello,
    I live in Toronto and have a mutual driveway about 5’4” wide. My neighbours have constructed 2 bathrooms (basement and powder room on the main floor). They were both vented through the wall into the mutual driveway. The powder room fan about 10 feet high and the basement bathroom about 30 inches high from the driveway. I would like to know what the guidelines/codes are as far as venting through a wall into a mutual drive. Can it be done? How high do the fans have to be off the ground? Thank you

  15. Manny says:

    hi, does a principal exhaust fan switch on a 3way have to be installed in a full house reno or new construction only? I have done some full house renos in the Toronto area and never required it by the stamped drawings nor the building inspectors. I came across a situation recently where the stamped drawings do not require it but the building inspector did… no hrv/erv are installed…. the top floor exhaust fan also required to be minimum 80 cfm and with a 6 inch duct,,,,the principal exhaust is located in a master bedroom … so,, what if that bedroom door answer as the ensuite bathroom doors are both closed… not very practical to remove humidity and to move air ….

  16. Don Morris says:

    I live in a 35 year old strata in BC. There are two bathrooms, one with a fan and the other with a window. The bathrooms share one wall and both are on outside walls, so the ducting is short. We would like to add a fan to the bathroom with a window only. To put a fan exhaust through the rain screening requires an engineer’s drawings and a rain screening qualified contractor. Can the duct from the new fan join the duct from the existing fan to exhaust through the same outside opening? Can you have a backflow protector on the ducting, so the air is not just blown into the other bathroom?
    Thanks, I appreciate your expertise.

  17. Mike says:

    Hello, I am building a new cottage and had the HRV drawings done. They show the bathroom and kitchen exhaust venting into the return duct.
    Do I have to do that or can I have the kitchen and bathroom exhaust right outside? I am not having a furnace installed I just have to have a Ventilation system. Cottage will be heated with a wood burning stove. It is registered as a 3 season cottage in the muskoka area.
    Thanks

  18. Edwin says:

    I’m looking after a condo building where the washroom exhaust fan on each floor is connected to a main duct that vented thru the roof. I check the airflow of each vent and found that on the lower floors the air is exhausting good while on the top floors the air is blowing into the washroom. I check the exhaust fan rotation and fire dampers but everything is good. What seems to be the problem then? Thanks

  19. marie says:

    Hi,

    I have been living in an older apartment building in Toronto for almost 11 years. Although the bathroom ceiling has a vent for a fan, there is no actual fan meaning there is no switch to turn on to ventilate the air. If your remove the vent cover, it just reveals a big hole which I’m assuming goes up to the roof. There have been times where I have smelled cigarette smoke, someone’s cooking and other odours that I don’t think I should be smelling in my bathroom. Even though there is no window or motorized fan, is the building still up to code? Thanks

  20. Jude says:

    Hi,

    Need suggestions of bathroom exhaust fans that can be wall mounted (exhaust directly to outsider of house), that are quiet and have a heat exchanger built-in

    The CFMs required are Bathroom (1) – 45 CFM; Bathroom (2) – 105 CFM and Bathroom (3) – 200 CFM

    Appreciate your comeback

    Thanks

  21. K Lee says:

    Living in a 12 old house built by a bigger, self claimed & believed by oridinary citizens to be good reputation builder in Waterloo, only to find out recently 2 of the 3 bathrooms (1 full, 1 powder room) were not connected to the outside vents. I fixed one by myself through the attic, the other one would need to break the drywall, I know it has passed the warranty time, should the builder be responsible to the fault they made at the beginning? Any process I can go after them? I e-mailed the builder and of course no response as usual, I experienced it 12 years ago.

  22. Max says:

    But it’s always better to know the professional opinion. Why not to call a plumber?
    And some more interesting information http://drpipe.ca/how-to-detect-a-gas-leak/

  23. Judi says:

    Hi there!
    Question for you – Our upstairs bathroom does not have a shower, we have a claw footed tub. There is a good sized window. We are selling our home. Is the bathroom requires, by code, to have an exhaust fan where there is no shower?

    thanks much, enjoy your site! Knowledge is power!

  24. David Wang says:

    My house was built in 2001 by Minto. Recently I want to do re-roofing, and found there is no exhausted vents for two bathrooms on the second floor. My neighbors’s have the vents in the soffits near the windows. But mine do have them. Maybe they forgot them installed and let the exhausted air to attic and hide in insulation. Does it violate the building code? How can I do about it?

  25. John Cazakoff says:

    I have a remote inline exhaust fan connected to both an upstairs and downstairs bathroom. Whenever the fan is turned on, it also turns on the central air conditioning for the entire house. Is this normal? It is quite annoying, expecially in the cooler months of fall, winter and spring, meaning we don’t run the exhaust fan nearly as long or often as we should.
    Thanks. for your help

  26. Jeff says:

    I was looking at a Nutone inline fan, ILKF120; one of the reviews told of the fan unit freezing solid in the winter. So do you box it in with a light bulb to prevent the freezing? Any other ideas?

  27. Fallon says:

    I live in an apartment and there are no exhaust fans in the bathrooms. The landlord said something about an exhaust fan in the main hallway by the laundry room that sends air under my front door. That doesn’t seem to make sense to me ? It is mandatory to have exhaust fans in the bathroom ?

  28. dale says:

    does bathroom venting go to soffit or roof sheeting by code?

  29. Paul says:

    I have a downstairs bathroom with no way for a exhaust fan to be installed without a ton and I mean a ton of grief. There is no window either. Is there a way to or is there a exhaust fan or system that does not need to be vented i.e. a filter type of system?

  30. Ted says:

    Great article on bath ventilation. In my line of work, installing bathroom fans I find that most existing fans are not vented properly. I always vent to the outside usually through the roof. I install only the Panasonic brand of fans since they are quiet and use less power to run.

  31. Kim says:

    I just read your information about properly choosing a bathroom fan. How do I measure for SP static pressure? By bathroom is about 10 x 5.5.
    Any help you can offer will be appreciated.
    Thank you, Kim

  32. Valerie Marie says:

    Is there a bylaw in Quebec for condo owners that stipulates the bathroom fan must be running all of the time, my son-in-law is under the impression this is so his bathroom fan is so noisy I would like it to be changed to a quieter one but do not want to I interfere ?

  33. Dale Wilson says:

    I have condensation returning to my bathroom during subsequent showers. My bath fan is vented straight up throught the roof with flex metal duct so obviously condensate is freezing to the inner wall of the duct. Would replacing the duct with plastic or poly duct fix the problem? I am in Edmonton, AB.

  34. Paul burnham says:

    Can I change the existing bathroom fan to in crease the outflow without going into the attic, home 30 years old original fan

  35. Kelly Killingbeck says:

    The builder did not connect the bathroom exhaust fan and the vent is blowing into the attic – therefore the mositure is just dripping into the ceiling and joists — the bathroom is also freezing as the heat source is not below the large window – Im afraid the pipes may freeze in this bathroom — what should I do – my tarion warranty is no longer valid as the unit was built in 2010 – there are definite problems with the bathroom

  36. James Poort says:

    When we install fans in a new build or renovation, we automatically included a timer switch – no questions asked. We do this because we feel it is more important than the quality of the fan (although this is important as well) to have the fan running well after the room has been vacated. We instruct clients to use the maximum time setting for the fan after a shower has been completed (usually 60 minutes). This will ensure that air is moving and the moisture is being reduced / removed from the air, which is crucial for preventing mold and mildew

  37. Bill Philip says:

    In these days HRV’s, Do we need bathroom fans. They seem redundant and another whole in the building envelope. Even on recirculate the HRV distributes the moisture through out the house with periodic make-up air. This makes a livable moisture percentage without humidification.

  38. Julie says:

    Help! Just found out that the first floor powder room ventilation was installed without a duct. When opening the second floor to refit a bathroom, the first floor ventilation was installed without even openening the vent seal. Since the floor and walls are open in the bathroom above, how can I duct my powder room vent to the outside through the attic using exising wall?

  39. Bill Philip says:

    Are we forgeting the HRV in the equation?The HRV is also removing air from the bathroom. The HRV will compete with the bathroom fan lowering the fans flow rate.
    The shortest distance and least torturest route would be the must desired from restriction point of view where to put the outlet.

  40. David Furlong says:

    Does the Ontario Building Code require an apartment to have a kitchen exhaust fan, and must it be external vented?

  41. David Kasrelevicius says:

    Thanks for your information. It is CLEAR and to the point. (I am an Master Electrician (Retired) and ….. I know who knows the subject.
    You are good.!!!

  42. Rachelle Durocher says:

    Is there a law that specify that your house/condo must have a bathtub? We live in Quebec.

  43. Ron says:

    How important is it to have a window that opens a few inches in the bathroom after a shower?

  44. Rose-Ella says:

    I have a bathroom laundry room combo. I don’t have a fan but have a window and dryer vent to outside. Is this sufficient or do I need a fan vent. Some tell me that a fan vent would needlessly lose my heat as I live in Canada with cold winters. They say that the dryer vent is sufficient. Di you know what does the code for New Brunswick say about that? I will appreciate any comments from you.

  45. Carol says:

    What type of ducting is up to code. I need to vent a fan for my basement to the outside but I am not sure what is code. I live in Ontario