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Bathroom extractor fan flexible ducting11/27/2023 ![]() Vent fans range from as low as 0.5 sone up to about 6.0 sones. (A modern refrigerator operates at about one sone.) Fans also have a sound rating, measured in sones. For example, a 100-square-foot bath would require a 110 CFM-rated fan. To determine which size fan to buy for your bath, multiply the room’s square footage by 1.1. The bathroom here is below an accessible attic, so Tom ran the exhaust duct across the attic and out a gable end.īathroom vent fans are rated by how many cubic feet of air they can move in one minute, known as the CFM rating. That’s why we asked This Old House general contractor Tom Silva to show us how. One reason many households still don’t have bath fans is that they can be intimidating to install. ![]() That way all you'll need to 'worry' about with condensation is the first couple of feet of pipe - and that won't be an issue at all.Ībsolutely wrap insulation - eg loft 'wool' - over that first few feet, but only bother with the remaining length if you feel like it - it shouldn't now matter.A bathroom without a ventilation fan is like a fireplace without a chimney: If you fail to pull the moisture generated in the bathroom out of there, it will migrate into the walls and grow mold and mildew, or blister paint and peel wallpaper. In which case simply stop the support plank a couple of feet before you reach the fan location so the ducting then - in a gentle curve - bends down towards it. ![]() How much higher would it need to be at the fan end? I dunno - but only the barest slope is required, so I can't see much more than a foot height being needed. Set this up with it's lowest point at the ext grill and then add increasing sizes of blocks on the joist tops as it makes its way back towards the fan. If it's flexi ducting, then it'll need something flat and supportive to sit on - so a 6m length of the cheapest softwood plank you can find, or similar. If so, I would try not to add any length to that - hopefully there's enough 'spring' still in the pipe to allow an extra foot or so of extension? I don't know what your setup is like, Disco, but I assume it's currently a ceiling-mounted fan (?) with the ducting (flexi concertina'd plastic type?) come up and bending gently over and then running along the loft joists until it gets to the external grill? Worse case is you'd need to replace the fan with a beefier model. Also, being the larger 150mm dia - it's already pretty free-flowing. An extra metre length on an already longish 6m probably won't make much difference, especially if the new pipe length is smooth plastic - far less flow resistance. Another simple solution is to leave the fan running for at least 5 minutes after the bathroom use so that the duct is effectively vented dry.īut, your own idea is probably as good as it gets - if you can get virtually all of that run sloping very slightly downwards towards the external grill, then jobbie jobbed. What does that leave? Insulating the ducting should certainly help a lot, as said above. I don't think I'd risk using the existing vent as there's a risk of smells coming back in! You can fit back-flaps, but I doubt these are air tight, and you really don't want sewer smells coming oot yer bathroom vent. ![]() Yeah, 6m is a fair distance - but you do have a large dia duct. Thanks, any advice would be greatly appreciated. Does that sound like a stupid idea?Īnother way to go about it would be to use a rigid pipe and create a fall toward the soffit to ensure the condensation running out, but I have a feeling that this would be quite demanding on the fan as I would have to increase the length by another metre or so to create the fall, and I am not sure how efficient it would be. I have read that one of the ways to avoid this is to shorten the duct, but I cannot do that, as the bathroom is in the centre of the flat and the 6m is already the shortest possible distance to the soffit and I cannot really cut a hole in the roof.īut since there is a vent pipe running through the loft and out the roof already (very close to the bathroom fan), I was considering connecting the extractor to the vent pipe using a Y piece (something like ), but I am not sure what side effects that could possibly have, like rain/dew dripping through the fan. Since the duct is quite long and the roof is not insulated, a lot of steam has been condensing in some of the sections of the duct (between the joists etc). My bathroom extractor fan is connected to a 150mm x 6m long flexible ducting which runs up to the attic and then across to a hole in the soffit.
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