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Is it code to vent a bathroom fan out into the garage?

15 years ago

Not sure if this should go here or over in Heating and AC??

Upgrading the noisy low CFM fart fan in our downstairs guest large bathroom to a nutone In line fan 250 CFM unit. I am not sure where the other 3" line ran off to . I see the old 3" hose is headed and can only imagine it turned and headed up 2 floors into the attic. If it did they had a 70 CXFM fan on about a 40' run in 3" flex duct. I have never seen it there. I swear it just vents into the furnace room About a 20' run and smells up the whole area and doesn't vent the shower moisture very well.

Just checking to see if its ok for code to vent this 6" line about 10-15'out into the garage?

Not sure if there is a fire related reason in the code or something. I don't think I have a choice. I will hook this fan up to a 15 min timer or else it sure could suck in alot of cold air in the winter.

I am also putting in a 1000w Dimplex 120 v wall heater.

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Comments (4)

User
15 years ago
No, it is against code to vent into your garage, and for good reason! You don't want that moisture in your garage either! It would condense onto your auto or freezer or anything else you have out there---accellerating rust and other issues exacerbated by moisture. This is precisely why you are trying to get the moisture OUT of your house! And, it's also against code to have any penetration into a garage not be fire rated. You could vent through the garage up into the attic and out the roof, but only if the venting material was covered by drywall. No direct holes from garage into the home allowed. That's why all doors into a garage are fire rated. BIG safety issue here! (Which is the reasoning behind most codes.)
elkski
Original Author
15 years ago
Thats what I thought. Would it be foolish to hook up a nutone ILF 250 6" size to the old 4" flex duct? I have to assume it goes somewhere.
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This is pretty basic. How do you plan a bathroom exhaust fan with no provision for ducting? Sounds like someone was a asleep at the switch. While it is possible to install a bathroom fan with no ducting and exhausting into an attic or joist space -- YOU DON'T WANT TO GO THERE!!! Have you ever heard of mold and dry-rot problems? You're just asking for both if you install a bathroom fan that isn't properly vented to the out of doors. Dumping all of that moisture into an enclosed space where it will be in contact with bare wood, insulation or exposed wallboard is a sure way to develop major problems over time. If there's a window in the bathroom, you'd be better off abandoning plans for a fan that exhausts into joist space. If there isn't a window, then you need to figure out a way of ducting the exhaust because an exhaust fan will be required by code.
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Thanks all, I finally got access to the condo's message board and got some help from another resident. He said the ductwork was there and said something about a "door" in the fan unit. I poked around inside of it again and lo and behold, a small piece of sheet metal fell off the side of it and there was the duct! The sheet metal piece had a piece of tape on it that I think may have been a hinge, of sorts--so that it would flap open when the fan was on and then fall back over the duct opening when the fan was off to keep drafts out. But a thick coating of greasy dust had kept it from working properly, and also made it hard to see that that's what its function was. The duct opening is only about 1x2", not the big 3" or 4" round opening that I was thinking it should be. It's still not a great fan but at least it's not blowing all of the air right back into the room! And I will have to figure out how to put that flap back on once the weather gets cold, but I have a bit of time before that will be necessary. PS-- no window in that room, unfortunately...
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A bathroom exhaust fan should produce 4 air exchanges per hour. Your bathroom is 7 x 7 which is 49sq.ft Assuming an 8' ceiling the total volume would be 49 x 8 = 392cu.ft We want four complete air exchanges per hour so that would be 392cu.ft x 4 = 1568cu.ft per hour. There are 60 minutes in an hour so we divide 1568 by 60min and it equals 26.13cfm. You currently have a 50cfm fan, which is twice the size you really require yet your having problems with the mirror fogging up. I suspect your problem is not the fan. Nature abhors a vacuum therefore a fan cannot push air out of a room unless there is provision for an equal amount of air to enter the room. You can test the theory by running the shower and leaving the bathroom door slightly ajar to allow more air to enter the room. Generally they make a slightly higer gap under the bottom of a bathroom door to allow more space for makeup air to enter the room but in some circumstances that does not provide enough makeup air. The solution then is to install a duct through the wall to an adjacent room and put a grille on either side. That will allow the additional air.
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"energy_rater, if you vent the humid air from a bathroom to the soffit, what's going to keep that moist air from going right into the attic?" back draft damper attached to bath fan housing. venting attached to back draft damper. venting exits soffit to exterior. fan being on will push air out of venting, venting to exterior of attic will keep moisture out of attic. also, if you ever take off the cover of the bath fan from inside the house..there is an oversized cut in the ceiling that is covered by the cover of the bath fan. sealing this cut is recommended to keep attic air/temps/ insulation particles out of houses. I use Hardcast brand mastic tape #1402. I also use this tape to attach back draft damper to housing of bath fan for air tight seal, and to attach venting to back draft damper. best of luck.
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elkski
Original Author
15 years ago
Ok my new solution is a proper one. Continue through the joists in this room and go out the front of the house.. ITs a brick wall but hidden behind a bush.
I have ordered one of those external plastic 6" flapper valve exhaust deals. My new question is will I need to insulate the this entire joist or just use insulated flex ducting.
Yes this is a cold climate.
lazypup
15 years ago
Unless your bathroom is 21' x 21' or equivalent a 250cfm fan is way too much.

Bathroom exhaust fans should be sized for 4 complete air exchanges per hour.

You begin by multiplying length x width x height to determine the total number of cubic feet in the room, then multiply by the desired number of air exchanges per hour. The result will tell you the number of cubic feet of air per hour that you must move.

You then divide the cubic feet per hour by 60minutes/hr to determine the required CFM.

By example, let us consider a bathroom that is 10' x 10' with an 8' ceiling.

10'x10'= 100sq.ft
100sq.ft x 8' for the ceiling = 800cu/ft in the room.
We desire 4 air exchanges per hour so we multiply 800cu.ft x 4 = 3200cu/ft per hour.

Dividing 3200cu/ft per hour by 60min/hr = 53.3cfm.

Thus a fan that is rated at 54 to 60cfm would give you the required 4 exchanges per hour.

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