Bathroom exhaust fan a big heating leak?

[CarbonNeutral]

Maybe close it off with a plate in winter - its not as if we don't need the moisture and warmth in the house in the winter - may have to shower with the bathroom door open :red:

 

[wahoowad]

I was up in my attic recently and noticed my bathroom exhaust fan vents bathroom moisture out to my soffit. I don't think there is any kind flapper or damper in there to keep ambient house heat from also escaping when the fan is not running. Of course my unit is over 20 years old (never replaced from original one installed). Doesn't this seem like a big heat wasting leak? Do newer ones come with some kind of damper?

 

[vgrund]

The new ones do have the flapper as stated above. The newer fan/light combos also more electrically efficient, mostly because CFL is a lamp option. If you replace it, give consideration to two things: CFM and to noise levels which vary widely. A lot of fans barely move any air and are a facade meant to satisfy building codes. Noise levels are usually rated in sones. Learn what that means and compare the ratings.

Panasonic makes some very nice and very quiet fans. I installed those in my last house. My current one has cheap builder grade Broan fans, which I hate.

 

[peakbagger]

I havent bought one yet, but one of these looks like the way to really seal up a bathroom vent http://www.houseneeds.com/shop/bathkitchen/tamarackbackdraftdamper.asp.

 

[burnham]

Most fans have a flapper mounted in them, but it doesn't make a very tight seal. You can get a better flapper and cut it in-line closer to the soffit. It also helps to insulate on top of the vent in the attic.

 

[velvetfoot]

I'd think an undampened duct would contribute to the stack effect, with the warm air moving out through the duct.
As has been said before, you can't check the temp there because it is hot air leaving.
I plan on using an incense stick to check for leaks this winter, plan being the operative word.
However, CN might have the right idea.
Perhaps assurance could be obtained with a cheap humidistat.

Edit: How'd that happen? I responded to a future comment!

 

[Gooserider]

I'd think an undampened duct would contribute to the stack effect, with the warm air moving out through the duct.
As has been said before, you can't check the temp there because it is hot air leaving.
I plan on using an incense stick to check for leaks this winter, plan being the operative word.
However, CN might have the right idea.
Perhaps assurance could be obtained with a cheap humidistat.

Edit: How'd that happen? I responded to a future comment!

The time waves have been in flux tonight - it seems to be taking a while to make them settle down properly...

On the original topic, that houseneeds damper looks nice, but I'm not sure it would do what some of us need - seems like the problem is often not that the fan backdrafts when off, but that the air keeps going out the fan vent in the same direction, just not as much. (I know that seems to be the problem in our house...) Judging by the description, it sounds like the HN damper would do very well at stopping a backdraft, but presumably do little or nothing to slow air that was moving in the same direction the fan would have been blowing...

What might be more interesting is a tight sealing flapper with some sort of solenoid or equivalent that would only let it open when the fan is actually on...

Gooserider

 

[velvetfoot]

The dryer really pushes out the air.
The bathroom vent, not so much.

 

[daveswoodhauler]

My new bathroom van pushes out a ton of air at 140 cfm....so much that when I turn it on I can feel a small breeze coming in around the door from the other room....basically sucking in air around the gaps of the door.

 

[velvetfoot]

I was just comparing to the dryer.
I've got a good vent on the dryer outlet but that really pushes a lot of air.

 

[jimmy dean]

The use for the fan mounted damper and the exhaust point damper is to prevent wind from forcing air back down the ceiling fan. For Soffit mount fan discharges the "under eave" type vent hood keeps the moist air from rotting the soffit and/or roof. The use of uninsulated flex plastic tube can-in cold locations- be blocked by condensation pools in the saggy pipe. If air didn't enter under the closed door of the bathroom the bath fan would not have air enough to exhaust out- you can't make that stuff in there!

 

[velvetfoot]

Subjective, I guess. Seemed pretty powerful to me.

 

[daveswoodhauler]

Found this...kinda what I was looking for...but seems pretty pricey for just a vent?

http://www.heyokasolutions.com/ProductDetails.asp?ProductCode=PRMX-SV2801&CartID=1

 

[jimmy dean]

try http://www.dryerbox.com/pages/undereve/undereve.htm these work

 

[velvetfoot]

I didn't see that one when I was looking.
It looks better made than the one I used:
http://www.hardwareandtools.com/invt/9261165

 

[daveswoodhauler]

Thanks Guys....found the one Velvetfoot listed on Amazon for like $4 smackers....I have a 6" pipe so I will need to use the reducer that came with the unit.
Had some other stuff to order from amazon....installation is going to be a PITA

 

[tutu_sue]

We also had an almost 20 year old bathroom fan that was so noisy it was like showering with a twin turbo prop in the room. And the mirror was still foggy when the shower was done. So we installed an Energy Star rated inline fan from a company called Fantech http://www.fantech.net/bathroom.htm . The fan is so quiet there is no audible reminder to turn it off, so we put in a timer switch. The fan is mounted in the attic with an insulated flexible duct to the roof. Both the fan grill in the bathroom and on the roof have spring dampers. Okay, not cheap but you can take the hottest shower and never even a molecule of steam on the mirror.

I don't know if this will work for your particular situation, but they have soffit and louvered vents for non-roof venting.

Also found out that our old fan was way underpowered for the size of bathroom from day one. Be sure when sizing this kind of fan that you use the CFM with .4 static pressure for duct losses.

Here's pics of the fan vent and the wall timer.

 

[jimmy dean]

The alternative to the set time switch is the use of a dehumidastat wired in parallell with fan switch. In cold weather set dehumidastat at 30-40% the colder the lower, clearing the mirror in the bathroom should take less than 15 min. On line 120 volt
dehumidastats are available in the $15.00-20.00 range

 

[Archie]

Maybe close it off with a plate in winter - its not as if we don't need the moisture and warmth in the house in the winter - may have to shower with the bathroom door open :red:

I like the way you think! :lol:

 

[velvetfoot]

I'm thinking the little flap is a cause for air loss.
I'm gonna try the incese.

Thing is, with these bathroom vents, there's not that much holding back the stack effect air pressure while the springs can't be too strong 'cause of fan back pressure.

 

[CarbonNeutral]

Maybe close it off with a plate in winter - its not as if we don't need the moisture and warmth in the house in the winter - may have to shower with the bathroom door open :red:

I like the way you think! :lol:

Did a quick comparison - we had visitors in the early part of the week = closed door. Ceiling absolutely dripping, but dry within a few hours (rel humidity is down as it's cold out). Later part of this week, no visitors = not even the mirror got steamy.

I would guess better insulation in the roof would help as the ceiling will be less cold for the water to condense on.

 

[velvetfoot]

Tried incense thing (note to self: get better smelling incense).
No effect on plume on either vents.
It's 51F out so stack effect not that great, I imagine.

 

[oconnor]

If you are curious about how much air is leaving the house, try the garbage bag trick - place a bag around a hoop ring, and raise it up to the fan, sealed at the ceiling. If there is discharge, the bag will deflate.

My experience was that most of the air leakage from the fan wasn't actually out the vent pipe, but around the poorly sealed fan itslef - the fan motor and pipe should be vapour-barriered (not sure that is a word) so that they are effectively inside the house envelope. When I installed mine, I used a plastic covered insulated sock around the piping, and sealed the fan iside the house envelope with plastic sheeting taped/acoustic caulked to the ceiling. There was no vapour barrier above the plaster, or I would have sealed it to the existing vapout barrier. The insulation on the pipe prevents condensation.

As a way of preventing passive loss out the duct, I ran the duct on a downward slope to the connector at the eaves, and installed an inline flapper that was weighted to allow for return to a closed position. When all was done, I used the garbage bag test with the fan off and on to guage the airflow.

Give it a try.

 

[velvetfoot]

Thanks. The garbage bag trick is interesting.