Any issues with bathroom ventilation in a floor?
A new home project with a crowded ceiling in a full bathroom. The question is where to locate the exhaust fan system, and while the ceiling is crowded, the floor assembly (to the crawlspace below) has plenty of space. So, the idea was to put an inline exhaust fan in the floor and run it out (wherever) and put a floor grille in the bathroom. The project team is a little freaked out with this approach since we just haven’t seen it done this way before, but I can’t find any fault with it. Other than the notion that moist air is less dense than dry air (meaning the ceiling would be a more likely place for moisture to collect, all other things being equal), are we missing anything?
The proposal is to run the fan continuously at ASHRAE 62.2 rates, so a reasonably well mixed room will get plenty of moisture removal.
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Luke,
From the stand point of odor removal it will probably work fine, but I'm not sure a constantly running fan, running at the low CFM that would practical or desirable, would be able to avoid the stratification that occurs when you get short lived but intense amounts of warm moist air that will accumulate near the ceiling. Some people have successfully used ERVs (with mixed success) in similar situations, but handicapping it by locating it near the floor I think would be asking a lot of it.
that stratification is the question... how much stratification do we really expect in a 100 sq.ft. bathroom? (not a rhetorical question). I would think that there is a sufficient amount of mixing Isuch a space and a continuouss operation of the fan (at say 30 cfm) would get the moisture out in a reasonable amount of time, especially if there's replacement air provided over the doorway. but maybe I'm wrong, which is why I'm asking the question.
There's a really interesting picture of moisture stratification in this just posted article:
https://www.greenbuildingadvisor.com/article/deciphering-problems-with-a-new-metal-roof
I also think it's desirable to have a bathroom floor you can wet mop without worry about water damage to a fan.
Can you put a vent high up on the wall?
Luke,
It's an interesting question and I can't offer anything data driven to answer it. Bathrooms definitely experience a lot of stratification when very hot, moist air is introduced during baths and showers - you can see that on large mirrors which fog up from the top down. My gut reaction is that the solution you are suggesting seems risky. No chance of including a bulkhead to avoid all the gymnastics and uncertainty?
You can get a bathroom fan that fits into a 2x4 wall (ie FV-0510VS1), I've used these a number of times and they work great. You can mount it on the wall up high somewhere and run the duct either sideways out the house or down through the wall. The outlet is 4" oval which is essentially a standard 4" hard pipe squished a bit. Once you are out of the wall, you can un-squish back to 4" round use regular fittings from there.
When you vent sideways, there won't be much of the wall stud left, so this can only be done in a non-loadbearing wall.