Hi,
How does one install an exhast fan when the joists run parallel to the outside wall. My prospective contractor recommends drilling holes in the joists. This is a larger bathroom so I need a larger fan so I am going to have 6" holes in my joints. Isn't that effectively cutting them in half? What could be an alternative solution?
Thanks!
Aaron
Why not just run the duct above the joists out to the wall? Or straight up through the roof? Or is this installation not on the uppermost floor? If the latter, how about a wall mounted exhaust fan?
nate
I'm going from memory here......holes in joists.
Never in the center 1/3 of the span, no notches
Must allow 2" min (1/3 of the joist depth?) between edge of hole & top or bottom of joist
If these "rules" are correct that means about a 2.5" hole max in a
2x8... ~3" hole in a 2x10Of course you could make aluminum (or steel) doubler plates to reinforce the holes in the joists
but in any case a 6" hole is pretty big you could go rectangular duct to minimize hole depth (like a 3 x10) might work. out ok but I'd still consider the doubler plates.
cheers Bob
Run the exhaust between the joists to the closest compatable wall. Use a fan compatable with a 3 or 4" duct otherwise, and reinforce the joists.
Look for another contactor
You should be able to find larger CFM fans that only use 4" duct. I don't think gouging out a good portion of your joists is a good idea. Another possibility is to build a small soffit to accommodate the duct.
NO!
If the contractor is a licensed "professional", he MUST be right and the homeowner MUST be wrong and is an idiot.
Just ask anyone on alt.hvac.
;^)
Eric Law
PS To the orig>> Hi,
At the risk of sounding silly, is there *no* way to run the duct between the joists rather than across them?
Even if it's a considerably longer run, it would be better than having the floor collapse ;^)
Eric Law
According to John Grabowski :
Or install more than one exhaust unit so you can use smaller venting.
6" seems rather extreme. IIRC, our main bathroom (9x18) could be vented properly with one high CFM (220CFM I think) fan with 4" duct or two fans with 3".Another possibility is to use multiple inlets with a blower mounted elsewhere. You could use smaller inlets (within reason) without paying the noise penalty if the blower is installed elsewhere.
Depending on the duct run, you can get good service from a smaller duct and use a good quality fan that can reduce to a 3 or 4 inch duct. I did the same thing in a weekend place, and have a 90 CFM Panasonic unit there that works great. It reduces to a 4" duct.
I cut an "oval" type notch in the joists impacted (accessed by lifting a section of upstairs floor) and used a flexible duct to allow it to gently change from round to oval where it crossed the joists. That way I only needed to cut 3" vertical in the duct, which did not greatly impair the load-bearing ability. The metal reinforcement is a good idea that I would have used if I was any closer to the center of the joist span.
Anyways, it worked great for me. It's about a 5 foot run, and very strong exhaust at the outside wall.
p.s. No way I'd drill 6" holes in any joists...
Well, here's the fan that I like:
Panasonic are good fans. The noise thing is very much a personal issue. Some people don't mind a louder fan as it provides masking sounds and it _sounds_ like it's working! Totally your call.
Someone touched on the remote blower - if you have another bathroom you could get a larger blower and run both ducts to it, then a duct to outside. That may let you run the ducting in a better way. Only thing with those multi-zone exhaust fans is that both rooms will have air exhausted when either bathroom switch is turned on. There are damper registers that are automatic. It's not a cheap way to go in any sense of the word.
R
According to this calculator you don't require that many CFM's:
You may find better prices here:
Not BS at all. We have a fairly nice townhouse that was built well in most respects. It is recent construction, done well, and the finishings were several grades above the standard tract level. The master bath is large with slate floors and granite counters. Along with this nice facade was a crappy contractor grade Nutone ceiling fan. It didn't work well, sounded like a Lear Jet winding up, and was a pain from the start. It always annoys me to see the hidden junk that [some] contractors will use to save a few bucks in an application like this.
Finally last year I replaced it with a 50CFM Panasonic unit (baby brother of the one the OP linked to). When I first turned it on, I thought I had wired it wrong, since I couldn't hear it at first.
We went with the 90CFM (or was it 80?) unit at our tiny cabin for two reasons. First the celing is low so it needs to be cleared of steam faster when showering, and secondly because the bathroom is right off the kitchen, and some privacy is a nice touch. Still the sound generated is very low compared to low grade offereings.
Go to a good supply place and see if they have demo units set up. Turn them on and hear/feel the difference. It really is quite an eye-opener.
There's more to figuring out the required air flow than the size of the bathroom. A whirlpool tub can require a much larger size fan than that calculator indicates. From that same web site: "Click Here For R.E. Williams Bathroom Fan Calculator (The result represents the minimum recommended cfm rating for your bathroom fan). You can view this link for a simplfied explanation of the recommendations of the Home Ventilating Institute for bathroom ventilation - Bathroom Ventilation Recommendations. Click Here For A More Technical method using a chart to properly size a bathroom fan. Remember, if you have a steam room, sauna, or hot tub, you will need to increase the size of the fan to compensate for additional moisture. "
Why add makeup air at all? Most houses aren't nearly that tight, and ones that are that tight probably already have an air-to-air heat exchanger (aka HRV). I can't see how opening a window helps at all. It'd be a net energy loss amongst other things. And that's pretty much what that Williams web site indicates:
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