Exhaust fan vent location

[atgcpaul]

I'm remodeling the master bath (2nd story) and want to move the exhaust fan.  The master bath is centrally located on the back wall of the house, but the current exhaust port is located on the far wall of the house about 25' away.  So there is a 25'+ metal duct that makes that run.  Our last exhaust fan was barely strong enough to push that much air and you could barely see the little flaps on the exhaust port open up when it was on.  Our current fan can push them open.  I figure a shorter run will make the fan work better.

The duct doesn't even run between the ceiling joists but on top of them so I have no idea why the builder went the long route rather than popping a hole in the back of the house 3' away from the fan.  The back wall location would put it in the proximity of the bathroom's window.  The new fan location would extend the run another 5', though.


So were there code reasons or some practical reasons why the exhaust port is so far away when it could have been located much closer?  I seem to remember that chimney's must be X distance/height away from a window.  How about bathroom exhausts?  Also on the back wall of the house is the exhaust for a 1st floor gas fireplace insert--looks like a big horizontal cylinder off the back of the house.  However, there are windows around that exhaust on the 1st floor so I can't imagine that's the reason.

Thanks,
Paul

[Robert Adams]

You don't want it near a soffit vent as the moisture will end up in the attic. Not a problem here but it is an issue in places that get much colder than us. 

      Here a vent fan vented through a wall is extremely rare. They are all vented through the roof (if they bothered to vent it outside)

[Splinter Puller]

Get a stronger fan.

[Duane N]

In my area if a bathroom has a window that opens no exhaust fan is needed. I would keep the exhaust port in it's current location (unless you want to abandon it and relocate it closer to the exhaust fan) and just relocate the fan so it has less ductwork to push the air through. You could also purchase a larger cfm exhaust fan just making sure the duct connection is the same (either 3" or 4" in most cases). The only code I follow when installing an exhaust fan is to keep the exhaust a minimum of 10' away from any outside air intake for an a/c unit....but that's commercial not residential buildings.

[Lynden]

I installed a NuTone inline exhaust fan to ventilate both of my upstairs bathrooms. The duct run is about 30 feet long and the fan is mounted near the end of the run about 5 feet from the outside wall.

http://www.nutone.com/products/filter/re...0b1c53a354

[WoodTinker]

My original bath fans was 2" from the fan to 3" round metal ductwork up to the triangular attic vents. One went to the front and the other to the back.

A long time ago I replaced my 2 upstairs bath fans.  Each had a 4" outlet and back flow prevention valves.

Using a DC wye connection I put them together and vented to the outside wall that was closer. I picked a vent with the outer covering to prevent bird nesting. I could watch birds going in and out of my neighbors vent with louvers without the cover.

I sealed up the 4" flexible metal tubing and encased it all in round insulation to help prevent moisture turning to liquid and pooling in the winters.

I see the moisture turning to frost below the vent, showing me that it works.

I did have to add screws to the inside of metal tube coming out the back and into the plastic vent to make it sturdy. The vent comes with a thin 4" metal tube that pops out too easily from the plastic vent. I only found one with a cover at HD.  My Lowes didn't have any with covers.


Gas burns very efficient as I think it only puts out co2 and moisture out the vent. 

How close would your bath vent be to the gas vent? If the gas vent is on the first floor and the bath vent on the second you should be fine.

[geek2me]

Using a DC wye connection I put them together and vented to the outside wall that was closer. I picked a vent with the outer covering to prevent bird nesting. I could watch birds going in and out of my neighbors vent with louvers without the cover.

So you have two fans feeding into one external vent?  When only one fan is running, how do you keep the air from flowing out the other fan intake instead of venting to the outside?  The higher SP of the vent would tend to divert the air into the other "intake" leg of the wye.

[WoodTinker]

Guess you missed the line:

Each had a 4" outlet and back flow prevention valves.

[daddo]

There's no reason I know of where you couldn't exhaust it to the roof right above the fan or near it. Longer runs are usually used to place the roof vent on the back of the house or where you can't see it from the street.
I'd surely use ridgid duct for better flow- perhaps a short metal flex to make it easier to connect to the fan.
In some areas, they insulate the outer surface of the duct to reduce condensation.

[geek2me]

Guess you missed the line:

Each had a 4" outlet and back flow prevention valves.

I saw that, but was assuming the "back flow prevention valves" were the flap type, which don't work that well.  Guess I should have asked - what type of back flow prevention valves are you using?  Where in the leg to the fan are they placed?