Bath vent recommendations
I’m replacing an undersized bath vent and its undersized duct. I’m mostly looking for recommendations on specific models, but I’ll take comments on sizing if you think I’m way off. It’s a typical bathroom — one shower, two sinks, one toilet. Climate zone 2, in case that matters, and the duct runs through a climate-controlled attic.
The bathroom is about 11.5 x 5.5 with a 9-foot ceiling, or about 570 cubic feet. That suggests a fan size of about 75-80 cfm, but I’ve got a long duct run to the nearest wall. I’ll install about 25′ of rigid 6″ duct. A each end will be short (about 2′) sections of 6″ flexible duct pulled tight at each end … or maybe rigid elbows if I don’t have to cut sheet metal. With that long duct, I’m thinking of upsizing to 100-110 cfm.
So, any suggestions on makes and models? Multiple speeds would be a bonus. I don’t need anything super-quiet, as the sound of a fan masks other sounds. Thanks!
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Replies
I would get one of the better ECM fans such as the Panasonic whisper green. These use much less power, way quieter and handle a fair bit of pressure.
You should be able to run everything in 4" duct, so for example if you have only a couple of bends and a hood, say around 60' equivalent length total, it can deliver close to 100cfm. Going up to 6" would only be needed if you have a lot of elbows.
Thanks. Those Panasonics do look very nice. I've already bought the 6" rigid ducts, because the existing 4" flexible was in bad shape.
I'm wondering if I should get the Panasonic model that's 50-80-110 CFM or the 110-130-150 CFM. Instincts tell me to go with the higher-powered model, which will allow for more imperfections in the flexible-duct sections at either end of the rigid duct. The bigger model also uses the same power at 110 cfm as the smaller one does at 50 cfm. I'm going to use it as a basic on/off vent for the bath, not planning to use any of the advanced features like continuous whole-house ventilation.
I have around a 9x8 bathroom with a 60cfm bath fan and 25cfm ERV pickup. The ERV pickup by itself is not enough, but both together are plenty of flow.
I guess since you have the larger duct, going with the larger one is possible. Not sure if it is worth the 2x cost though unless you have some major humidity issues in the bathroom.
The flex duct at each end might be good for sound, but if it's because of a strange shape consider whether you can use a rigid elbow (the ones with four turning bits can be combined to make a longer radious turn, apparently those turnings bits are called gores ;) and then correct with straight sections of angled flex? ie I'm just repeating the advice about being sure not to bend the flex sharply (I've also seen elbows put inside to maintain the opening).
Are you planning to slope it to the outside for internal condensation?
That's a good idea to link adjustable elbows to make longer-radius turns. I hadn't thought of that.
I am planning to slope the near end upward so I can slope the far end downward to drain any condensation to the gable vent. That's part of the reason for using the flexible duct at that end, to make the connection easier. It's generally pretty warm here (Gulf coast), and the attic is climate-controlled, so condensation is a limited cold-season issue, and I'm thinking only the last few feet of the duct are a concern.