I am installing vents for 3 bathrooms and a dryer and want to vent them through a single opening in my roof.
It is a 2 story brick ranch with asphalt shingles
There are 2 bath fens upstairs and one down with a dryer that needs a roof vent
Tired of seeing the dryer vent coil through my garage and out of a rear window
Will I induce any unnecessary moisture problems by combining these vents?
Should consider a damper of some sort?
If so where?

Hey EES:

So 3 bath fans and a dryer vent... huh?

Sorry...my opinion...can't connect the dryer vent into those bath fans....just can't be done!!

You need to penetrate the outside wall with dryer vent (if possible) by renting a small rotary hammer drill and a sawzall... or keep as it is... but cannot connect into the fan vents.

Why.. The moisture that is coming out of that dryer vent would vent out the roof, but much of it would also reform as moisture in the walls of pipes and would most likely POOL and eventually run down pipes and into fan units and that is not a good thing... never mind the electrical connections to these fans!!

I understand your thinking... thinking, well, fans pull moisture out of air and therefore already have this moisture I'm talking about.. but that is not accurate.

Bathroom fans don't REMOVE moisture from a bathroom... they actually move AIR... circulate AIR if you will... and it is the movement of the air that causes the walls to dry. Fans in these units simply aren't strong enough to actually remove moisture from a room (yes some gets by... more steam condensating inside vent pipe... very little... maybe few droplets).

My POINT:

These fan units are not meant to deal with the moisture that could return down the pipes from a dryer connection. Don't do this!

I hope that all made sense... let me know what you think.. ok?

Mark

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Mark I am confused. The bath exhaust fan certainly does remove moisture by exhausting the air outside the building and allowing home air to get pulled into the bath. I do however agree that you can't combine those fans and dryer. The exhaust fans have a back draft door on them but they are nowhere near air tight and would allow dryer fumes to enter the baths. When I install exhaust fans they are pretty specific about the size of the duct, length and number of elbows. Each fans wants its own run.

Hey Bob... the way it was explained to me by nutone rep. was exactly how I wrote it above...

"Bathroom fans don't REMOVE moisture from a bathroom....they actually move AIR...circulate AIR if you will...and it is the movement of the air that causes the walls to dry. Fans in these units simply aren't strong enough to actually remove moisture from a rooom".

If I understand it correctly.. as a result of the air circulation the water actually EVAPORATES and disappates into air. The rep. was very clear about the fan not being strong enough to move water/moisture itself.

I argued how I could watch steam go into the vent after/during shower and he said that SURE.. a little was getting moved into unit... more so by virtue of rising than getting pulled into unit.

He said... the FAN pulled air into room and the air caused water to dry!

That's what he said anyway... kinda made sense... especially after the STEAM phase was over and remaining water droplets dried on wall right in front of our eyes.

BUT believe me, I would not bet wads of cash on this... ;) Just what the rep. told me.

Let me know if you find different... Mark

"He said...the FAN pulled air into room and the air caused water to dry!" I think this is key, plus that guys doesn't know what he is selling. It does pull air into the room because it push moisture loaded air out the exhaust vent. Some of thes fans are rated 60 cfm, so that's 60 feet of moist air removed and 60 cfm of house air pulled inside. The room air reached its dew point and water condensed on the walls and mirror, no evaporation can take place at or above the dew point. The evaporation happens when the fresh air well below its dew point is pulled inside. I guess the most important thing here is we agree that Steve should not try to bring them all together into one vent.