# Bathroom Fan, or not?



## Hurriken (Jul 7, 2008)

Our master bedroom has a half bath. No tub no shower. It has a ventilation fan installed in the early eighties and I was planning to update it. The existing fan has an 8"x8" housing and the new fan has a 7-1/2"x7-1/4" housing. While I'm sure it would work I would have to do some patch work on the corners to be able to cover the opening with the vent cover. 

The new fan is 70CFM. I could buy an 8"x8" fan for double the price that is 80CFM. I'm wondering which choice would be better...or do I even need a fan at all?


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## Bob Mariani (Dec 1, 2008)

a vent fan should be used since you still have a sink and toilet both which will produce moisture that needs to be removed. Size of the fan depends on the size of the room


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## Scuba_Dave (Jan 16, 2009)

I always install a fan, especially with a toilet
70cfm is all you need
Depends upon if you want to patch


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## Hurriken (Jul 7, 2008)

OK So what your saying is there is no issue with the fan box being a bit smaller. I have no problem patching, we need paint in there anyway. 

Right after I posted this I read German House Rebuild and now I feel like a wimp!


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## Termite (Apr 13, 2008)

The code requires a fan in all bathrooms, even half baths (an exception is made if the room has an operable window, but it is a stupid exception in my opinion). The only thing that will really be an issue in there is smells...No humidity from showers...So you don't need to put a huge fan in there. That being said, a larger fan will clear the room out faster. :wink:


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## RegeSullivan (Dec 8, 2006)

70 CFM in a your 1/2 bath will be fine. Most important, be sure the fan is venting to the outside and there is a source for air to enter the room when the do is closed. 1 1/2" of space at the bottom of a 32" door should be enough.

Rege


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## Hurriken (Jul 7, 2008)

I was concerned that, with the smaller fan box, I would lose heat through the spaces. I plan on installing a much larger fan in the full bath even though the room is not that big.


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## Gary in WA (Mar 11, 2009)

8 air changes per hour for the cubic feet of space in the room is the minimum per code. Who wants a minimum of anything? lol. 
Be safe, Gary


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## Termite (Apr 13, 2008)

GBR in WA said:


> 8 air changes per hour for the cubic feet of space in the room is the minimum per code. Who wants a minimum of anything? lol.
> Be safe, Gary


I'm not familiar with that one...Can you give a code section?


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## Hurriken (Jul 7, 2008)

Actually one of my concerns is that the old system does not vent to the outside. They ran the pipe up to the false chimney. I guess it does go out but from what I've read it should vent out of the side of the house and not the roof.


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## Gary in WA (Mar 11, 2009)

I'm not familiar with that one...Can you give a code section?From Kc. Because I said it wrong...... Nothing gets by that guy...The UMC code is still 5 room air changes/hr. ? 1203.3 20 cfm minimum. That's even less! Thank you for catching that, Kc. 

This article recommends 8 changes, from HVI: http://www.efi.org/factoids/bathroom_sizing.html Notice too, the use of corrugated pipe and increase suggested, as well as pipe size changes for higher cfm's. 
I would vent through roof, not into chase. The roof mount exhaust is 5-10% more efficient at removing warm, moist air (hot air rises) than a side mount one. Roof terminal should have a pipe neck attached for a positive connection. Use straight pipe (metal or PVC) whenever possible, wrapped with insulation. Corrugated, flex, pipe creates turbulence and has almost double the surface area for water exhausted in baths to collect on. Use as few bends as possible, and 45s* instead of 90s*. Tape metal joints with silver tape, not duct tape (4 year life). Tape the individual joints of each elbow. Use 3 screws on each metal joint. Use HVAC black tape for plastic covered insulation. Insulate the whole pipe and the fan *box. *Use caulk to seal the small gaps at the fan to wallboard joint. Let no heated moist air escape into the attic which would cause mold, mildew, wet other insulation (defeating its purpose), possibly making frost in your attic and ice dams on the roof. 

Be safe, G


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## Termite (Apr 13, 2008)

All good advice there GBR!!! :thumbsup:


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## Hurriken (Jul 7, 2008)

This great information but at the same time I'm not sure if it is what I wanted to hear. The house was built in 1982 and as far as I can tell the configuration has not changed since then. I have found no mold or moisture damage. The fans look to me like contractor models and seem a little cheap. I also believe they are low CFM. The pipe is corrugated flexible tubing but it is short. The main bath is probably only 5-7 feet from the vent and the 1/2 bath might be ten. The concern is the vent. They fastened the pipe to the inside of the false chimney. To me it looks a bit lazy but I was hoping I can keep it like this because I am afraid to cut a hole in the roof. Not so much cutting the hole but reworking the shingles afterward. This turns what I thought would be a quick job into a big job. I have other things to do you know, the honey do list isn't getting any shorter! 

Anyway, I am going to do away with the flex pipe. My wife is a penny pincher and I can't say I disagree, no sense throwing money out the window...or through the fan pipe.:jester:

Please tell me I can vent through the false chimney.


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## Hurriken (Jul 7, 2008)

I was able to install both new fans today...just the fans. It was much more work than I expected. It was really hot in the attic and I spent most of the time either on my belly or crouching. My whole body hurts! 

Since the half bath was smaller than the existing hole I took a piece of aluminum flashing and cut a piece that would fit the fan and cover the hole. I will tape it with silver tape tomorrow. I may add caulk from the ground side to fill in the space, do I need to do this?

I finally broke down and called my dad, he is the best DIY guy I know. He used to fix everything when he was younger. He told me the city would disapprove of the vents discharging into the false chimney. He encouraged me to make a hole in the roof (I'm very nervous about this)and use regular duct to vent the fans. Now I have more questions.

One fan has a 6 inch exit but it came with an optional 4 inch step down. I was thinking about running 4 inch duct straight up from that fan through the roof. Then I would run three inch from the 1/2 bath fan and splice it into the 4" pipe. Is that good thinking?


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## Bob Mariani (Dec 1, 2008)

your plan will work fine.


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## Ed the Roofer (Jan 27, 2007)

Coincidentally, this OP has just contacted my office to have two separate Broan Vents installed on his roof section sometime mid next week.

Good advice from everyone else so far too.

Ed


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## Hurriken (Jul 7, 2008)

I lost touch with Ed and have had little luck finding someone else to do this. I looked into some handymen but they want to run the vents out of the soffet. I don't think that is the best option. Could I install vents on the roof myself? I'm really nervous about it.


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## skymaster (Jun 6, 2007)

IMHO I would NOT reduce to 4" then connect the 3". Stay at 6" thru the roof, "T" in and reduce to the other sizes, Also be sure u place a damper in line besides the little ones in the units.


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## Hurriken (Jul 7, 2008)

OK I'll remember that but how do I install a vent in the roof?


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## skymaster (Jun 6, 2007)

Pick a spot easy to work in, remember to keep it visually below the peak, this keeps it from being seen from street if that is important, be sure to work in CENTER of a bay, mark the center punch a big nail thru. Now go to roof,carefully un nail and peel back shingles, IF possible roll back the top paper, cut the required hole, slip the roof hood under the top sheet, keep it over the lower paper, nail it home, re shingle. Now go back into the attic, make all your connections. Simple :yes::laughing:

Now if all this sounds a tad daunting :}:}:} CALL ED AND GET HIS BUTT OVER THERE


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## Hurriken (Jul 7, 2008)

Finally, I did it myself! It wasn't so bad. Of course it hasn't rained yet...:boat:
I think I did OK though. Picture #2 looks a bit funny at the top because I hade to jerry rig the top adapter. I think it will work fine though. #2 is a half bath so there isn't much moisture anyway.


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## spark plug (May 5, 2009)

RegeSullivan said:


> 70 CFM in a your 1/2 bath will be fine. Most important, be sure the fan is venting to the outside and there is a source for air to enter the room when the do is closed. 1 1/2" of space at the bottom of a 32" door should be enough.
> 
> Rege


Glad you pointed out that the OP should make certain that the fan is venting to the outside. Because I found on some service jobs, that the --bathroom exhaust fan-- was venting into the attic. In some cases due to the section of flex pipe being disconnected and in others it was never connected to the outside. (No matter what) Don't Drink and Drive, Ever!!!


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## Hurriken (Jul 7, 2008)

Why does there need to be a space for air to enter the room? My wife thinks it is sucking the heat out so she closes the register and puts a towel under the door.


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## RegeSullivan (Dec 8, 2006)

It is sucking some heat out of the house and along with it super moist air (or bad odors) created in the bathroom. If air did not enter the room, air would not leave the room once you created enough vacuum to overcome the power of the fan. Chances are you will not be able to create a tight enough seal to overcome the power of the fan with towels and closing the register but it is reducing the efficiency of the fan. You could accomplish the same effect with a little more control and convenience by installing a speed controller for the fan.

The bottom line... You want the moist air out of the house. It causes damage and reduces the efficiency of most insulation. The heat loss is a trade off and not a major cost unless the fan is on for many hours everyday.

Rege


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## Hurriken (Jul 7, 2008)

RegeSullivan said:


> It is sucking some heat out of the house and along with it super moist air (or bad odors) created in the bathroom. If air did not enter the room, air would not leave the room once you created enough vacuum to overcome the power of the fan. Chances are you will not be able to create a tight enough seal to overcome the power of the fan with towels and closing the register but it is reducing the efficiency of the fan. You could accomplish the same effect with a little more control and convenience by installing a speed controller for the fan.
> 
> The bottom line... You want the moist air out of the house. It causes damage and reduces the efficiency of most insulation. The heat loss is a trade off and not a major cost unless the fan is on for many hours everyday.
> 
> Rege


Thank you for the excellent explanation. Today we notice that we can now hear outside noise through the fans. It is a bit annoying right now but I still need to insulate the pipes and the fan box. I hope that helps. 

I was looking around, I think I'm the only one on my block that vents the bathroom fans outside.


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## spark plug (May 5, 2009)

Hurriken said:


> Thank you for the excellent explanation. Today we notice that we can now hear outside noise through the fans. It is a bit annoying right now but I still need to insulate the pipes and the fan box. I hope that helps.
> 
> I was looking around, I think I'm the only one on my block that vents the bathroom fans outside.


If what you're saying is true, we're in big trouble. (Just kidding). (No matter what):laughing::no::drinkon't Drink and Drive, Ever!!!


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## Hurriken (Jul 7, 2008)

Here are the vents. I'll have to get on the roof to get a better picture. They are facing west.


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## Hurriken (Jul 7, 2008)

Regarding insulating this, what do you mean by a "blanket"?


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## Bob Mariani (Dec 1, 2008)

what you want to use is insulation wrap. An insulation blanket is more for an electric water heater.


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## Hurriken (Jul 7, 2008)

Thanks Bob.


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