Roof only, and preferably through vents made specifically to accept the type
of duct normally used for such fans. The previous owners of my house did
sort of a hack job, using coat hanger wire to attach the duct to a normal
roof vent. Somehow, this hasn't caused problems, but when I re-roof soon,
it'll be fixed anyway.
If you don't have the guts like me, you can run the ductwork close to
a vent in the roof. I have an attic fan, and I ran my exhaust duct
close to the vent. I know this is not the correct way to do it, but I
did not want to risk any leaks by opening up my roof.
If the bathroom doesn't have a shower/bath then going into the roof
would be OK since you're not venting any moisture. I just put to
bathroom fans in my house, I just had a roofer guy install the vents.
I bought them at Home depot and he just charged me $75 to install
Some tips when doing this.
1. Over size the fan. If the chart says 80 CFM go with at least 100
You will never be sorry that your fan works too well. It will also
let you have longer ductwork and reduce the possibility of getting
I put a 110 in a 8x8 bathroom, and the shower can't even fog the
2. Use a timer instead of a switch.
3. If you have a roofer install your vent, get up on the roof and mark
want the vents, or be there when he's installing them. My roofer,
despite detailed drawings and measurments, still managed to put one
vent in the wrong spot, which made me use a lot longer duct length,
but still seems OK.
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