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Helpful? 1

Bathroom Exhaust Fans

Bath fans help remove odors and moisture — and can be used in some homes to satisfy whole-house ventilation requirements

Posted on Aug 7 2014 by Martin Holladay, GBA Advisor

Older homes often lack bathroom exhaust fans. In the old days, if the bathroom was smelly or steamy, you were supposed to open a window to air it out.

This isn’t a very logical ventilation method, especially when temperatures are below zero, or when the weather is 90°F and humid. Yet this time-honored method of bathroom ventilation is still enshrined in our building codes. According to the 2009 International Residential Code (sections R303.3 and M1507.3), a bathroom with an operable window does not need to have a bath exhaust fan.

Why do we need exhaust fans?

In spite of the code’s archaic loophole, builders should install an exhaust fan in every bathroom or toilet room — even when the bathroom has a window.

A bath exhaust fan can perform several functions:

  • It can exhaust smelly air, allowing fresher air to enter the bathroom.
  • It can exhaust humid air, allowing dryer air to enter the bathroom.
  • When operated for 24 hours per day or when controlled by a timer, it can act (in some cases) as the most important component of a whole-house ventilation system.

Designing an exhaust-only ventilation system is a topic unto itself, and is beyond the scope of this article. For more information on exhaust-only ventilation systems, see Designing a Good Ventilation System.

Where does the makeup air come from?

When the bathroom door is closed and the fan is operating, where is the makeup air coming from?

If the bathroom has an exterior wall, some of the makeup air is coming from the exterior — for example, through leaks around the window or baseboard.

Some of the makeup air is probably coming into the bathroom from other rooms in the house, via the crack between the bottom of the door and the flooring. Of course, if the bathroom fan is exhausting 50 cfm, then 50 cfm must be simultaneously entering the building. If some of the makeup air is entering the bathroom through the crack under the bathroom door, an equivalent volume of exterior air must be entering other rooms of the house through a variety of random cracks in the home’s envelope.

Unfortunately, many exhaust fans pull some of their makeup air through a nearby crack: namely, the crack between the housing of the fan and the ceiling drywall. You don’t really want attic air to be entering the bathroom through this route, so fan installers need to remember to seal the drywall crack around the fan.

What happens if homeowners don’t operate their fan?

Homeowners sometimes worry that if they fail to operate their exhaust fan, the bathroom ceiling will stay damp and every surface in the room will soon grow mold. That’s not necessarily the case; in fact, some bathrooms without exhaust fans stay dry and mold-free for years.

What factors affect mold growth?

  • A small bathroom is more at risk for mold growth than a large bathroom.
  • A bathroom that includes a shower that is used frequently is more at risk than a bathroom with a rarely used shower.
  • Bathrooms with airtight walls and ceilings are more at risk than bathrooms with lots of infiltration and exfiltrationAirflow outward through a wall or building envelope; the opposite of infiltration..
  • In cold climates, bathrooms with poorly insulated surfaces are more at risk than bathrooms with well-insulated surfaces.

All building inspectors encounter moldy bathrooms at some point. The extreme case is a small bathroom used daily by many members of a large family. In many cases, the main factor leading to mold growth is missing insulation above the ceiling. During the winter, cold drywall stays damp. That’s why ceiling mold often occurs near exterior walls, where insulation tends to be thin. Repairing insulation defects helps prevent mold: the insulation keeps the drywall warm, reducing opportunities for condensation or moisture absorption.

Needless to say, even bathrooms that aren’t at high risk for mold growth still need a fan.

Testing an exhaust fan

Just because a fan makes a comforting noise (or an irritating whirr), doesn’t mean it’s moving any air. Many such fans are totally ineffective.

The classic home inspector’s method for testing a bath fan is the toilet-paper test: Remove one square of toilet paper from the handy roll nearby; then turn on the fan, and see if the fan is strong enough to hold the square of toilet paper tight to the ceiling grille.

In some cases, the toilet paper falls on the floor. With a little bit of investigation, you should be able to figure out whether the duct in the attic is crushed or whether the termination is filled by a bird’s nest.

If you need an accurate measurement of an exhaust fan’s flow rate — for example, to comply with requirements of the Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. Home program — the toilet paper test won’t cut it. Instead, you’ll need to measure airflow with a device like the Energy Conservatory’s exhaust fan flow meter.

Achieving 50 cfm

According to most building codes, a bathroom without an operable window must have an exhaust fan with a minimum ventilation rate of 50 cfm (assuming intermittent operation) or 20 cfm (assuming continuous operation).

In the past, many builders and code officials interpreted this to mean that the fan should be rated at 50 cfm. There’s a problem with this approach, however: once a duct system is installed, a 50 cfm fan might only be moving 25 cfm. (The reduction in airflow rate is due to the static pressure of the duct system.)

Most green building programs now require that the airflow rate through a bath exhaust system be verified to determine that the fan and its associated ductwork are moving at least 50 cfm. (This rate of airflow is usually plenty, by the way. You don’t really need a big honking fan in your bathroom.)

Some green builders have been surprised to learn that their 110 cfm fans are failing the 50 cfm performance test. In other words, they didn't realize that the static pressure of a duct system can seriously affect airflow rates. What’s going on? All of the usual culprits are implicated:

  • The use of flex duct instead of smooth-walled duct.
  • The use of ductwork with too small a diameter.
  • Too many elbows in the ductwork.
  • Sloppy installation practices leading to convoluted ductwork.

In a 2013 blog, Allison Bailes told the story of a developer who installed bath fans rated at 110 cfm in several new Energy Star homes. The developer assumed that a 110-cfm fan would be powerful enough to overcome sloppy duct installation and still pass the 50 cfm test. That approach didn’t work very well, since 4 of the 9 fans flunked the test.

Let’s say that your fan is hooked up to a funky duct system, and it’s only pulling 35 cfm. There are two solutions to this problem: you can swap out the 110 cfm fan for a more powerful model — say, a 200 cfm fan — or you can fix all the duct problems. (A good duct system has a large diameter, smooth walls, and few elbows.) Either approach will work, but the latter approach is preferable — because the system will use less energy and will be quieter.

Fan makers have begun to respond to reports that builders are failing the 50 cfm airflow test by offering more powerful fans. For example, ads for Panasonic’s EcoVent fan boast that the fan includes a booster switch that a builder can flip to ramp up the fan’s speed if the fan fails its airflow test. While that solution is easy for the builder, a better solution would be to fix the funky ductwork.

Static pressure and fan ratings

Every duct system has static pressure that limits air flow. Most exhaust manufacturers rate fan performance at two different static pressures: 0.1 inches of water column (i.w.c.) and 0.25 i.w.c. Since the installed duct system for a bath fan is likely to have at least 0.25 i.w.c. of static pressure, you should ignore the unrealistic numbers in the 0.1 column when you’re looking up fan ratings.

Some fans have lower airflow rates (in cfm) at 0.25 i.w.c. than at 0.1 i.w.c., as one might expect. Other (more sophisticated) fans — those with electronically commutated motors — have airflow ratings that are roughly equivalent at the different static pressures. These ratings are counterintuitive. Here’s the trick: these models automatically ramp up the fan in response to duct systems with a high static pressure. At higher static pressure, these fans are more effective than less sophisticated fans, but they also use more power (in watts) to achieve the full airflow they provide.

Ideally, you want to keep your maximum duct length to 10 feet of less — 20 feet in a pinch — with no more than three elbows. (Each elbow has the equivalent resistance of 15 feet of smooth metal duct, so you don’t want any extra elbows.)

Smooth duct is preferable to flex duct. If you decide to use flex duct instead of smooth-wall duct, the static pressure of your duct system will increase.

If your duct system is especially long or convoluted, or you ignore the advice in this article and install flex duct instead of smooth-wall duct, you will need to specify a more powerful fan to account for the high static pressure of your duct system. (For more information on this issue, see A Buyer’s Guide to Bath Fans.)

Choosing an exhaust fan

Perhaps your exhaust fan is noisy. Perhaps it failed the toilet paper test. You’ve decided that it’s time to buy a new exhaust fan.

A good exhaust fan:

  • Is properly sized: neither too wimpy nor too powerful.
  • Is energy-efficient.
  • Is quiet, since a quiet fan is more likely to be used than a noisy fan.

How many sones?

Fan noisiness is measured in sones. The lower the sone rating, the quieter the fan.

Higher static pressure makes fans noisier, so exhaust fan manufacturers list sone ratings at 0.1 and 0.25 i.w.c. For a realistic sone rating, look at the rating at 0.25 i.w.c. It shouldn’t be hard to find a Panasonic or Broan-Nutone fan rated at less than 1 sone at 0.25 i.w.c.

Energy efficiency

If you want an efficient fan, look for an Energy Star model. Qualifying fans are divided into two categories.

Fans rated at 89 cfm or less must have a minimum efficiency of 1.4 cfm per watt when tested according to the HVI 916 test procedure.

Fans rated at 90 cfm or more must have a minimum efficiency of 2.8 cfm per watt.

The Energy Star program also establishes maximum sone ratings. Fans rated at 139 cfm or less must have a maximum sone rating of 2.0 sones when tested according to the HVI 915 test procedure. Fans rated at 140 cfm or more must have a maximum sone rating of 3.0 sones.

Anyone interested in researching specifications for bathroom exhaust fans should probably consult the data published in the online directory of the Home Ventilating Institute.

Installing an exhaust fan

It’s important to follow the installation instructions provided by the manufacturer of your bathroom exhaust fan. In addition to following those instructions, remember these principles:

  • Verify that the bathroom door has enough of an undercut to allow air to enter the bathroom when the fan is running.
  • Remember to seal the crack between the fan housing and the ceiling drywall with caulk.
  • Verify that the backdraft damper in the fan operates smoothly, and hasn’t been taped shut at the factory.
  • Plan ahead to make sure that duct runs are as short as possible.
  • Install the fan so that the duct outlet is aimed in right the direction — toward the planned exterior termination. If it’s pointed the wrong way, you’ll have to start out the duct run with two 90° elbows, and that’s a bummer.
  • In many cases, it’s a good idea to install ducts with a larger diameter than the duct outlet on the fan. If the duct is longer than usual, use 6-inch duct instead of 4-inch duct.
  • Use galvanized duct or thin-wall PVC pipe. Joints in galvanized duct should be secured with sheet-metal screws and sealed with HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. tape. To reduce noise transmission and simplify installation, many installers use a short (generally 2 feet or less) length of flex duct between the fan and the rigid ductwork.
  • In a cold climate, attic ducts must be installed in a way that limits condensation. A duct that will terminate at a gable wall should first rise to an elbow that is high enough above the fan to allow the installation of a long run of horizontal ductwork that slopes slightly toward the exterior. (This encourages any condensation to find its way out of the house instead of dripping from your ceiling.) Wrapping the ducts with vinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate).-faced fiberglass duct insulation reduces condensation.
  • Support ducts every 3 feet with hangers or strapping to prevent sagging.
  • Verify that the louvers (if any) on the wall termination or roof termination are operating smoothly.

If possible, exhaust fan ducts should terminate at a gable wall. Roof terminations can work, but you’ll usually encounter fewer problems if you put a hole in your gable wall than if you put a hole in your roof.

In no case should a duct be terminated in an attic or at a soffit. (Soffit termination grow icicles during the winter, and allow humid air to be sucked into the attic in all seasons.)

How should an exhaust fan be controlled?

Operating a bath exhaust fan exacts an energy penalty:

  • It takes electricity to run the fan.
  • The fan pulls exterior air into your home through cracks, and this exterior air needs to be heated during the winter and cooled during the summer.

Because of the energy penalty associated with fan operation, fans should be no more powerful than necessary, and should be operated only as long as required.

The simplest way to control a bath fan is to wire the fan to come on with the bathroom light. This method works, sort of, but isn’t ideal. It’s better if the bath fan runs for 5 or 10 minutes after every shower.

This can be accomplished with a “delayed off” switch (for example, the Lutron Maestro) that keeps a fan running for a set amount of time after the switch is turned off. The delay is user-adjustable.

It’s also possible to install a humidity-sensing switch that turns a fan on whenever the indoor relative humidity reaches a preset level. This type of switch usually includes an override switch allowing the fan to be turned on regardless of the humidity level. These switches can be irritating; they often require seasonal adjustments, since normal indoor humidity levels are often higher during the summer than they are during the winter.

Some fans — for example, Panasonic’s WhisperSense fan — include sophisticated controls that incorporate motion sensors, “delayed off” features, and humidity controls. For more information on the WhisperSense fan, see A Smarter Bath Fan.

Operating your fan

Some experts have proposed rules for operating bathroom exhaust fans. Every family is different, however, so it’s hard to establish rules that apply to everyone. There’s no reason to run a bath fan for 15 minutes every time someone uses the bathroom.

If your bathroom seems damp, you probably want to run the bath fan more often, or run it longer after every shower.

If your bathroom seems dry and pleasant, you may not need to operate your fan as much as you are now.

Martin Holladay’s previous blog: “A Canadian Editor Questions Passivhaus Dogma.”

Click here to follow Martin Holladay on Twitter.


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Image Credits:

  1. Image #1: Panasonic
  2. Image #2: Greenhomesamerica.files.wordpress.com
  3. Images #3 and #4: Fine Homebuilding
  4. Image #5: LuxuryMetals.com

1.
Thu, 08/07/2014 - 13:03

Zoned Ventilation?
by rjp :

Helpful? 0

Humm... A central zoned ventilation system with automatic dampers, passive intakes and single ECM motor (actually available). Where does an actual ERV (energy recovery ventilator) or similar system fit when it comes to bath ventilation requirements?


2.
Thu, 08/07/2014 - 13:54

Response to RJP
by Martin Holladay, GBA Advisor

Helpful? 0

RJP,
Q. "Where does an actual ERV (energy recovery ventilator) or similar system fit when it comes to bath ventilation requirements?"

A. Your question is rather vague. But I have a hunch that this article will answer your question: Does a Home with an HRV Also Need Bath Fans?


3.
Thu, 08/07/2014 - 14:18

the tissue test
by Alexander Bell

Helpful? 0

While the tissue test may be a venerable home inspector classic, it really needs to be retired from the toolbag. Unless you place tissue over the all of the intake vents, you are only evaluating airflow at the location of the tissue. I have flow tested a fan that passed the tissue test, but the damper was still taped closed from the factory. No air was leaving the bathroom, just pulled in one side and pushed out the other.


4.
Thu, 08/07/2014 - 14:49

Response to Alexander Bell
by Martin Holladay, GBA Advisor

Helpful? 0

Alexander,
Thanks for your comments. I agree that it's a pretty crude test. But it has allowed me to identify a few fans that weren't pulling any air at all.

The main advantage of the toilet-paper test is that it doesn't require any equipment.


5.
Thu, 08/07/2014 - 22:04

installation
by Malcolm Taylor

Helpful? 0

Martin, The usual method of installation has a number of shortcomings. Relying on the supplied housing is problematic both because of the number of holes they contain and the small lip for sealing to the drywall. Using the housing also means that the most problematic joint, at the damper, is usually inaccessible once drywall is installed - as is the damper itself.
To get around this, on the last two houses I built I mounted an air-sealed plywood box in the ceiling large enough to contain all of the common fan housings. This puts the damper and connections inside the box allowing easy access for connections, removes all problems of air sealing and also means that the whole fan, including housing, can be changed out without any disruption of the building envelope. The only downside is that you have to buy a larger vent cover to use instead of the one that comes with the fan, but in most cases this is a plus as the ones they supply are usually fairly ugly.
If this seems like too much work I'd still recommend doing as the BC Building Envelope Guide For Houses recommends and mounting a piece of plywood flush with the ceiling framing to provide a larger and more secure surface to seal both the fan housing and drywall to.


6.
Thu, 08/07/2014 - 22:52

Location of terminations?
by Roy Goodwin

Helpful? 0

You recommend against roof terminations ( I understand that, I think poking holes in your roof is against nature) but also state "In no case should a duct be terminated in an attic or at a soffit.". I guess that means if you have a hip roof, you're stuck with a roof termination ?


7.
Fri, 08/08/2014 - 04:51

Edited Fri, 08/08/2014 - 04:52.

Response to Malcolm Taylor (Comment #5)
by Martin Holladay, GBA Advisor

Helpful? 0

Malcolm,
I salute your attention to detail. It sounds like you are paying attention to airtightness and anticipating future repairs. Good work.

Of course, most production builders aren't going to go to the trouble of installing a bath fan the way you suggest. But your approach is admirable.


8.
Fri, 08/08/2014 - 04:53

Edited Fri, 08/08/2014 - 05:08.

Response to Roy Goodwin (Comment #6)
by Martin Holladay, GBA Advisor

Helpful? 0

Roy,
You're right. If your house has a hip roof, you'll be venting your bath fan through the roof.


9.
Fri, 08/08/2014 - 12:30

Mold vs. Farts
by Kevin Dickson, MSME

Helpful? 0

It's worth mentioning that high humidity in the bathroom is really only a problem when it condenses on a surface. Well insulated bathrooms with no thermal bridges really reduce the condensation problem.

Also, I believe that the amount of air needed to dry out a bathroom is many times more than what's needed to dilute smells. Has anyone seen data on that?

Smells can also be removed without dilution, using activated charcoal filters. This may become a less expensive and more energy efficient way to handle the little toilet rooms and 1/2 baths/powder rooms. Half baths never have humidity problems, so why run unnecessary ductwork?


10.
Fri, 08/08/2014 - 14:29

Response to Kevin Dickson
by Martin Holladay, GBA Advisor

Helpful? 0

Kevin,
You wrote, "It's worth mentioning that high humidity in the bathroom is really only a problem when it condenses on a surface. Well insulated bathrooms with no thermal bridges really reduce the condensation problem."

You're right that it's worth mentioning -- which is why I mentioned it. I wrote, "In cold climates, bathrooms with poorly insulated surfaces are more at risk than bathrooms with well-insulated surfaces. ... In many cases, the main factor leading to mold growth is missing insulation above the ceiling. During the winter, cold drywall stays damp. That’s why ceiling mold often occurs near exterior walls, where insulation tends to be thin. Repairing insulation defects helps prevent mold: the insulation keeps the drywall warm, reducing opportunities for condensation or moisture absorption."


11.
Fri, 08/08/2014 - 14:40

also agree that a bathroom
by Jin Kazama

Helpful? 0

also agree that a bathroom without bath or showers ( what is the english term for such a "pipi room" ??) should not have an exhaust fan in any energy conscius design.

Kevin : do you have experience with quality filters ?
hard to find locally up here ..everybody still install exhaust fans on every room with a toilet fitted

An HRV with variable speeds activated by a control panel that monitors humidity and runs on fixed low speed to match required CFM .


12.
Fri, 08/08/2014 - 15:06

Roof vs. wall termination
by Nick Welch

Helpful? 0

I'm particularly interested in the arguments for terminating the duct at the roof vs. the wall, as I still need to do this for both my bath fan and range fan. Martin, I was surprised you so swiftly dismissed roof vents, though not too surprised, given your roofing background.

Here's my thinking: The roof is completely out of sight (on the rear of the house), while a wall vent would be visible. The roof is also a shorter duct run with fewer bends, because neither of my fans are very close to a gable wall. However, it seems like rain might be slightly more likely to find its way into a roof vent, and there is no way to direct condensation out the vent -- it will drip down into the house. I'm not in a very cold climate though, so I don't think condensation is a big concern.


13.
Fri, 08/08/2014 - 16:03

what is the number 1 building
by Jin Kazama

Helpful? 0

what is the number 1 building related problem ( #1 as in the most serious )
= water entry related dommage

so why put vents through a perfect protection surface ?
Roofs should be completely free of any entry points

why not shoot it straight out to the wall ?? who cares about how it looks
just invest the money saved on the tubes and roof sealing toward a better looking grille
and voila! :)


14.
Fri, 08/08/2014 - 16:24

Roof venting
by Nick Welch

Helpful? 0

Jin, roofs have plenty of penetrations. Roof vents (for attic ventilation), plumbing stacks, etc. The plumbing stacks leak fairly frequently because they usually rely on a neoprene gasket that deteriorates, but roof vents cover themselves with sheet metal in a way that seems to be pretty reliable.

Also, I figure a roof leak will be noticed and fixed ASAP. A wall leak can go unnoticed and cause a lot more rot before it's found.

And who cares about looks? Most people.


15.
Fri, 08/08/2014 - 17:09

i know everybody cares about looks,
by Jin Kazama

Helpful? 0

it was sarcasm ..

not because regular old type pushes "easy" roof penetrations we need to still go with this method


16.
Sat, 08/09/2014 - 04:41

Edited Sat, 08/09/2014 - 04:43.

Response to Nick Welch
by Martin Holladay, GBA Advisor

Helpful? 0

Nick,
Arguing about which is better, a roof termination or a wall termination, is a little bit like arguing over which is better, exterior basement insulation or interior basement insulation.

Either approach can work, as long as it is detailed properly. And folks with hip roofs don't have a choice anyway.

There are a lot of variables. Roof terminations are a particularly poor choice in snowy climates, and are much more difficult to install if you have concrete tile roofing than if you have asphalt shingles. But as long as you know what you are doing, a roof termination can work fine.

[Note to GBA readers: I'll be on vacation next week, but I'll be back at my desk on Monday August 18. If anyone wonders why I'm not answering questions during that period -- now you know.]


17.
Sat, 08/09/2014 - 07:11

Edited Sat, 08/09/2014 - 07:41.

An Ocean of Air
by John Brooks

Helpful? 0

Hi Nick,
Nothing wrong with "Arguing"....
I think "thru the roof" at least deserves some consideration/discussion.
Considering that the exhaust fan may not be operating 24/7....
What's wrong with having a "Flue" or "Chimney" that "connects" to the outdoors at a higher altitude rather than lower?

"We live at the bottom of an Ocean of Air"
In a tight house there are not-so-many openings that "connect" to the outdoors (Ocean of Air).
The termination of the exhaust fan may actually be one of the few "significant" openings.
The size and altitude of the significant openings are what determines the altitude of the Neutral Pressure Plane(NPP).

Doesn't a "chimney" thru the roof usually work better than a chimney thru a sidewall?
(It's possible to run a stove chimney out a sidewall ... but perhaps not ideal)

And even if the exhaust fan is running 24/7 .... why not work WITH the atmosphere?

Of course ...If the vent passes thru a cold attic ... the "conduit" should be insulated.
and in "Snow Country" the termination should be insulated and extended.


18.
Mon, 08/11/2014 - 11:45

Why not a soffit vent?
by Richard Patterman

Helpful? 0

It is not in the roof, it is not highly visible and it is protected from rain & snow.


19.
Mon, 08/11/2014 - 22:49

Reply to Richard
by Malcolm Taylor

Helpful? 0

The soffits often have vents to provide air into the roof space. You don't want them to draw the moist air that was just exhausted from the kitchen into the structure.
In an unvented roof the danger is that vents that terminate on the soffits can cause rot to the surrounding soffit material - although I've never seen it.


20.
Wed, 08/13/2014 - 18:24

Small baths with and without showers
by Mark Heizer

Helpful? 0

Thanks Martin for metioning that small baths have greater risk: rate of moisture production per room volume overwhelms small baths, even if there are no exterior wall or ceiling exposures: 103F water vapor is going to create problems. And an "oops" I noticed in my bathrooms: the high aeration rate of many low flow shower heads put more water vapor into the air stream than the old 2.5 head.

Unfortunately for many homes, multple kids (or entire families in apartments) share the 8x5 bath, while the parents share the mega-volume master bath. Guess which bath has water dripping from the walls and ceiling after back-to-back showers? 50 CFM (delivered) exhaust is questionable for a small volume, high-use bath unless you have the run-time switch or humidity sensor (FYI: one of these control options and 80 CFM is required by Oregon code. This was the result of a construction claims task force report).

The HVI guide has good information. But in my opinion, once the room gets above 200 SF, a bigger fan is a waste.

As for the 1/2-bath/powder room, these should be allowed 25-30 CFM (*hello 62.2 and I-codes*). Energy use isn't going to break the bank since the fan isn't used on every use. I designed projects with the "chemical" filters (true fart fans) in baths for a national chain. they're not effective for anything other than air mixing. An effective filter would use more fan energy than the combination of a 30 CFM intermittent exhuast and its infiltration/OSA energy penalty. Add the environmental impacts for filter manufacturing and disposal and filtration is laughable as a green option for masking natural bodily functions. Americans aren't ready to accept the powder room is actually used for something other than powdering your nose; so I suspect that elimation of the fan requirement isn't going to happen. Final note to builders: I've met homeowners that don't want low sones in the guest/half-bath and might want the timer switch. Many guests appreciate a little background noise...just in case; and ability to run the fan after you leave can be a real face-saver ("You may want to wait a few minutes, Bob.)


21.
Wed, 08/13/2014 - 20:55

Edited Wed, 08/13/2014 - 20:57.

Who installs your bathroom fans?
by Mike Guertin, GBA Advisor

Helpful? 0

We need a new subtrade - Bathroom fan installers. Ideally the HVAC (maybe better referred to as the heating/air conditioning) sub who is used to dealing with ducts should install them but many don't deal with whole-house ventilation never mind measly bathroom fans. Around here bath fans are installed by electricians - go figure.
Like many house components bath fan installation involves a few subtrades - electrician, duct installer, sider or roofer, interior carpenter (to undercut the door) and there may be others.
And then there is the brand / type of fan - who selects it and are his/her criteria based on performance or aesthetics? Since there may be a few tradespeople involved, and a client, the contractor needs to be on top of things otherwise it's just another detail that falls through the cracks.

I checked an exhaust fan for a friend of a friend. The premium fan was rated at 180 cfm and the flow hood read 38. It had all of the install problems Martin outlines and then some. I asked who installed the fan - "We had an electrician install it." Soon as the weather cools a bit we'll spend an hour in the attic and an hour on the roof correcting the problems.


22.
Thu, 08/14/2014 - 00:00

Edited Thu, 08/14/2014 - 00:01.

Mike
by Malcolm Taylor

Helpful? 0

Here the builder selects and installs the fan. The electrician connects it, like any other appliance, as they are the only trade licensed to do so.


23.
Mon, 08/18/2014 - 08:06

Wall mount fans
by A. Bradford

Helpful? 0

Is there any efficacy to the use of direct wall mounted fans in situations where the duct would be hard to properly route? Particularly in cold climates, would it be a recipe for infiltration/condensation?


24.
Mon, 08/18/2014 - 10:01

Response to Asa Bradford
by Martin Holladay, GBA Advisor

Helpful? 0

Asa,
It often makes sense to install a wall-mounted fan, especially in a house where ducting a ceiling-mounted fan would be difficult. The main advantage of a wall-mounted fan is that there is very little static pressure (a major problem with systems that have long, convoluted ducts).

A wall-mounted exhaust fan should be installed as close to the ceiling as the wall framing allows. It should be installed near the shower (but not in the shower stall).

Backdraft dampers that come with bathroom exhaust fans are not airtight, and there are technical reasons why it's difficult to make them airtight, so some air leakage is inevitable. However, the air leakage problems associated with bath exhaust fans exist regardless of where the fan is mounted.


25.
Mon, 08/18/2014 - 12:06

Asa and Martin ...
by Jin Kazama

Helpful? 0

As Martin pointed out, leak from damper is inevitable, however,
if you use a combination of products such as :

http://tamtech.ca/cape-dampers-20.html

and a mechanical damper that usually comes with the bathroom fans,
you might be able to reduce unwated leaks to a minimum.

The drape damper excels where mechanical dampers fail, wich is at very low pressure , where it should be sitting most of the time on a bathroom exhaust fan.

I've been wondering about using a double setup as passive inlet for make-up air for quite some time, but i have yet to try it out.

You can even use those on range hoods ( again best is to use a spring loaded quality damper near exterior output and a drape dapmer further in at inner wall line approx ... )


26.
Mon, 08/18/2014 - 19:24

How much undercut
by Paul Barraza

Helpful? 0

Is there a rule of thumb for how much under cut is needed for a 50cfm fan?


27.
Mon, 08/18/2014 - 20:13

Response to Paul Barraza
by Martin Holladay, GBA Advisor

Helpful? 0

Paul,
Paul Raymer calculated that a 1 inch gap under a 30-inch wide door is good for 47 cfm. If the bathroom has other cracks, and most do, then you can get away with a smaller undercut.


28.
Tue, 10/07/2014 - 13:00

Edited Tue, 10/07/2014 - 13:02.

importance of the fan
by Hari Kamboji

Helpful? 0

I have a new small bathroom with shower, no window, no fan, in a finished attic. I expect that the shower will only be used about a dozen times a year. Since the exterior "wall" is the roof, I think the only option for a fan terminus is straight through the side of the roof. I'm in the planning stage of redoing the roof with exterior rigid insulation, so it might be the right time to do the bathroom fan. But I'm not convinced that a fan is really a good idea in this case, where the bathroom will only be used occasionally. (I don't like the idea of piercing the roof and the resulting heat loss- I live in a place that gets significant snowfall.)


29.
Tue, 10/07/2014 - 13:09

Response to Hari Kamboji
by Martin Holladay, GBA Advisor

Helpful? 0

Hari,
The decision is yours. It sounds like you understand the pros and cons of each approach.

Keep in mind that building codes require an exhaust fan in this location. If you ever decide to sell your house, this code violation could be a problem.


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