Need help planning ventilation in bathrooms

8 years ago

Our HVAC contractor wants to just install basic 80 cfm fans in all of our bathrooms (new construction). After years of dealing with mold and mildew in our current home due to poor ventilation, I am not happy with this plan. We have 3 bathrooms that we are trying to plan ventilation for:

1. Our master bath will have a doorless shower (I have heard many opinions about that, but we are staying with doorless and can always add a door if needed). We will also have a soaking tub and the closet will be off of the bathroom. I would rather have overkill on the ventilation in this room, especially because of the closet. Here is a floor plan:

It is about 180 sq ft with the closet. I am thinking two fans would be necessary in this space. I am also thinking a heater might be nice in shower area. Both windows in this space open, but we are in an area where it is very cold in the late fall/winter/early spring. Any suggestions?

2. The next bathroom is a Jack and Jill with doored area to a shower/tub combo with shower curtain and toilet. It does have a operable window in the shower. The way the plans currently have it is a combo light fan, but that can be changed. Should the fan go directly over the shower and then have a ceiling light over the toilet? This room is only about 40 sq ft.

3. Finally, we have a bathroom in the basement. This is your standard basic bathroom. It is about 5 feet wide by 10 feet long. It has a combined shower tub (probably shower curtain). Again, vent over the shower or just in the center of the room?

We haven't had the electrician or HVAC contractor start, so we would like to make these decisions now. I really want to do everything I can to avoid musty, mildewy bathrooms! Also, any grout you suggest that is resistant to stains and mold? I am thinking epoxy but am worried about large sand with tight grout lines.

Thank you!!!!

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User

8 years ago

last modified: 8 years ago

But, this plan does have a separate water closet compartment, and the code specifically calls this "-even if it's in a separate room" out as mandatory for a reason that is obviously not for shower steam ;D .....So much for your theory of the intent of the code.

The two fans can always be used in conjunction with each other to clear the whole room of steam. A sentry stands just outside the gate for a reason. After installing thousands of bath fans, I can tell you that it is the most effective way.

I can also tell you that the fan usually ends up over the toilet by popular demand. It is never because people think it will get rid of the stink better that way. It is because the toilet is usually between the shower and the vanity mirror on the same wall. It goes closer to the toilet wall instead of centered on the 5' tub because people don't want to see it in the mirror when they primp. And, most think it "looks" like it belongs there from a design standpoint. Yes, I have asked every one of the homeowners for the thousands of fans I have installed where they want it, and why. The only thing I tell them is that I won't guarantee it inside the shower, and that it should be somewhere between the shower and mirror.

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User
8 years ago
last modified: 8 years ago
A rule of thumb is 1 cfm per square foot of bathroom. You don't need to include the closet. Another recommendation is 8 air changes per hour, or cubic foot of room divided by 7.5, which is usually a little more than 1 cfm per square foot. The separate toilet room needs its own fan. The minimum size is 50 cfm. So, if you need 130 CFL total, that could be 50 in the toilet room, and 80 just outside the shower. If you try to put a fan IN the shower, it will rust quickly regardless of the fan rating. Extra condensation in the duct can also become a problem since you would be extracting steam that would usually just condensate inside the shower area, as well as what gets outside. Without an adequate makeup air system, you won't be able to maintain more than an actual 50 cfm exhaust with the door shut to the bathroom. Air won't go out if it can't come in. The furnace would need to be actively pushing air into the room at the time the fan is running with the door closed to get enough air for an oversized fan. In the US, a range hood over 400 cfm is required to have dedicated makeup air. In Canada, ANY exhaust (over around 100 cfm?) must have a makeup air source from outside the house, including bathroom and dryer vents. This is due to the fact that new houses, and houses in colder climates are more airtight, and the windows don't get opened enough. Even if you leave the bathroom door open, you can still backdraft other fuel burning appliances such as furnaces and water heaters, causing carbon monoxide problems. Fresh, outside makeup air will more efficiently extract moisture than just a bigger fan. You may want to look into a heat recovery system for your bathroom fans since you live in a cold climate. Otherwise, your heating bill goes way up when you turn on large bathroom fans. The Jack and Jill bathroom will also need two fans if the toilet and shower areas are separated by doors. (I might be reading that wrong) The usual exception to this is that you don't have to have a fan in the area that has an operable window. I usually put the fan in the ceiling between the shower and the mirror to intercept the steam, or over the toilet because it looks like it belongs there. Just as important as a big enough fan and makeup air is a timer so that the fan can continue running for 20 minutes after you shower, and the bathroom door is open, and a quiet enough fan so that it will be used all the time. If a fan is too big, it can also make the room feel drafty, which isn't good either.
housebuilding126 thanked User
User
8 years ago
A fan is not necessary over the toilet !

You may want one there , but odor won't ruin you house. Warm moist air will rot your house and is the reason for bath fans in the first place.

I'd consider one over the bathtub also. People just don't realize how much moisture they add to the air. I disagree with Fred re: fan in the shower. There are plenty of choices that will function and last in that environment. The amount of moist air that passes through it isn't really that different if it's in the shower or 1 foot outside it.

Steam showers are a different animal , but you've not mentioned that.

Most important things are to have a timer switch on all of the fans and to use smooth wall piping for any duct run longer than 3-4 feet.

p.s. - your contractor will try and talk you out of the smooth wall piping unless he's really top notch.

Ive used the best/broan/nutone 744 fan light with good success in my three homes.
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User
8 years ago
Since the water closet compartment is the room without a window, it is the only one REQUIRED to have an exhaust fan by CODE.

R303.3 Bathrooms.

Bathrooms, water closet compartments and other similar rooms shall be provided with aggregate glazing area in windows of not less than 3 square feet (0.3 m2), one-half of which must be openable.

Exception: The glazed areas shall not be required where artificial light and a local exhaust system are provided. The minimum local exhaust rates shall be determined in accordance with Section M1507. Exhaust air from the space shall be exhausted directly to the outdoors.

.

.

And it is no coincidence that 95% or more of the calls I get to fix bath fans are for ones directly over the shower. Even the ones I have found that promote better over shower reliability have the same motors. The rust on the motor is what trips the GFCI every time someone tries to turn them on.
User
8 years ago
Fred - most of the bathrooms in the USA don't have a separate WC room and the builders think the only fan in the bathroom is a fart fan and it goes over the toilet - even if it's in a separate room.

As I've stated - the real purpose of the fan and the intent of the code is to remove warm , moist air from the dwelling . Not stinky smells.

So you guys do what you want , but your house is better off with a fan nearer /in the shower that gets used everyday multiple times and produces humidity than you are with a fart fan.

Those folks that have separate rooms within their baths for the WC can certainly afford multiple bath fans and the makeup air apparatus if necessary.

1. fans closest to the producer of the humidity you want to get rid of.

2. Smooth wall ducting

3. Timer switch so the fan can run after you've left to adequately exhaust that humidity.

the rest is gravy....
homepro01
8 years ago
last modified: 8 years ago
Dreamhouse,

Consider something like the fantech or Panasonic. These units have remote motors and you can have as many outlets as you want. I own the Panasonic Whisperwarm and it is get unit but it is a stand alone unit.
User
8 years ago
last modified: 8 years ago
Fan location as you lay out may have been the case after WWII Fred. Not in today's homes. And in this case 26 will have to have two fans minimum because locating only one in the WC will be practically useless for the shower in the opposite corner of the bathroom.

I've yet to see a fan housing or motor failure after 20+ years of them in showers , but I'm glad it's lucrative business for you. Good thing for you builders still use builder grade fans, but like homepro says , use a remote blower , and that would absolutely put an end to your replacement biz. A quality unit will also last the lifetime in a shower.

Use that broan 744 I mentioned and your customer will think you swindled them and didn't even install a bath fan ! It eliminates the visual objection anyone might raise.

Listen, I'm not looking for a tussle, but so far you haven't made your case that odors from the WC (in a compartment or not ) are more detrimental to a home than the gallons of water vapor produced by a typical shower. And , that being the case - locating the apparatus to remove that vapor will function better if it's closer to the source of that vapor. Which, you don't deny or dispel either. All your saying is the government knows best for us and most people want. Those are poor justifications in my view for dispensing advice.

All you're saying is that you wouldn't locate a fan in a shower because you've replaced thousands of them. Fair enough , but two people have given the community easy workarounds to your objection: buy a quality fan or use a remote system. And I've had exactly the opposite experience with that placement, so people can takeaway what they will from that.

Remember popular demand is the same thing that gave you all those fans to replace in the first place. Builders and naive home buyers love cheap and fast products - especially when it comes to infrastructure and mechanical systems.
User
8 years ago
last modified: 8 years ago
You can't possibly have 20 years of knowledge about anything since you read like a first grader. If you start reading from the beginning, you and the rest of the world will see that I am the one that said there will need to be 2 fans, and that YOU are the one that said;

neu2you

Yesterday at 5:34AM

A fan is not necessary over the toilet !

Just because you stuck your foot in YOUR mouth right out the gate, doesn't mean you can start putting words in mine trying to make yourself look better.

Where in the world did I ever say that "odors from the WC (in a compartment or not ) are more detrimental"?? I have said "and 80(+ cfm) just outside the shower" from the start, and "It is NEVER because people think it will get rid of the stink better that way."

I also suggested a heat recovery system (remote blower) before you ever showed up.

Nobody said "government knows best for us" but YOU. All I said was that "your theory of the intent of the code" was wrong. Neither the code, or myself intend to get into a debate about which area is more important to have an exhaust fan, as it is a moot point since both places are REQUIRED to have "ventilation" PERIOD.

I never said I have "replaced thousands" of fans. I INSTALL thousands of fans, even now, not back at WWII. AND, they are 99% all BROAN/Nutone. So are the ones I repair or replace, including the 744. If you think 20+ years is lasting "a life time", then you are still wet behind the ears. (Neu really does suit you for a name, I bet they call you that at work) That is when most of them go out, although some go out within a couple years, depending on the habits of the inhabitants. Most people are still paying off their mortgage at 20+ years. How would YOU like it if your car was worthless and had to be replaced before it was even paid for? In contrast, I have yet to need to replace a fan less than 35 years old that is placed just outside the shower.

And, what are you planning on doing for the steam you get when filling the tub with hot water, just add a third fan? SURE, you could, but these people are not just building this house "virtually" on the web. REAL MONEY doesn't grow on trees.

It appears, that in your 20+ years, you have made the same mistakes for 3 houses and leave them just as things start falling apart, and you get that 7 year itch.

Frankly, I would never want the extra draft you get by pulling cooler air into the shower area when the fan is in there with you.

Need help planning ventilation in bathrooms

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