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Old 10-24-2007, 03:53 PM   #1
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bath exhaust fan questions

hi - read thru the threads here (bath exhaust fan related questions) and still not clear on a few things

1) looked at the Broan fan display at local h/w store - they say it's fine to mount their bathroom fan on a wall as opposed to ceiling - but will this not significantly affect the fan's effectiveness to remove all the damp air (what happens to the stale air above the fan, against the ceiling - isn't this kinda trapped?)

2) my original plan was to just use a roof vent - then today someone told me to avoid venting thru the roof - they said this will only cause problems later (warm air flows out and melts the snow in the vent area, the you get ice buildup, eventual leaks, etc.) - so is it better to go out to the nearest exterior wall, run down the wall cavity, and then go out the wall instead?

3) I saw a soffit vent package in the store - this looks easiest of all - but I'm wondering if pushing the moist air out the soffit is a good idea - won't it just get sucked right back into the attic space as outside air moves thru the soffit and up to the ridge vent...?

this is new bathroom - and the roof is just being shingled this week - so i have any option available to me right now - just want to make the best choice to avoid problems in the future....



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Old 10-24-2007, 04:17 PM   #2
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Hi Randy,

I have installed many bath fans, in many different locations over the years and have found that some ways tend to work better than others. The dissadvantages to going on an exterior wall and the cieling are fairly common sense in that you can have problems with vapor bartrier penetrations and insulation deficiencies/condensation problems. I haven't experienced a lot of problems related to the termination locations, other than if you are in an area where you may accumulate a lot of snow on the roof or something of that nature causing some concerns with roof vent termination.

I have had some success with installing the fan near the top of a interior wall and venting down the wall space (using a pipe in the wall of course) to the basement cieling below and taking the exhaust out between the floor joists to the exterior of the house, like you would a dryer vent. the only downside to this method is that you need a fan with some decent push as it is pushing the air down and out, instead of horizontally or vertically and out. That is why I try and use solid pipe as much as possible as it cuts down the restriction a lot.

Don't worry about the air at the very top of the room. Your fan is only going to be a few inches off the cieling and the humidity will quickly mix with the surrounding air, taking it out the fan without any unussual problems.



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Old 10-24-2007, 05:06 PM   #3
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thanks Dave

feedback is much appreciated

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Old 10-25-2007, 03:46 AM   #4
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Keep in mind that there are two types of fans for moisture and odor removal. The type to use depends on whether you need to run ductwork or pipe.
If you need to run duct/pipe, install the type that has a blower wheel with a cfm rating of at least 2-1/2 to 3 times the cubic air space. When stale air is exhausted, it is not 100% stale as there is fresh air mixed in with it. So it does take a few minutes to remove all traces of stale air. Try not to use collapsable type duct as they offer more resistance to flow.

If you have an outside wall in the bathroom, then you can install a propeller type fan. Follow the manufacturer's recommended cfm rating for your air space.
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