Venting bathroom throught soffit?

mikeysmith

Is it a bad idea to duct a fan out through the soffit?

Does much of the moist air get sucked back in through nearby air vents as reported?

And does wind direction matter when using the soffit?

fred funk }{

I have mine vented through the soffit with an in-line fan and there no moisture at all coming back in as I have checked regularly.

mikeysmith

Thanks

Do you have attic vents near the fan outlet?

Do you know if the wind direction matters with a soffit?

Would you get anything blowing back?

fred funk }{

Nearest vent is about 2 ft away. Not sure about wind direction but the fan has a one way flap that only opens when extracting and closed to wind coming back in.

MicktheMan

mikeysmith wrote: »

Is it a bad idea to duct a fan out through the soffit?

Imo, yes it is a bad idea to duct a fan out through the soffit for a couple of reasons;
1. Huge reduction in fan capacity depending on duct length & type to the point of rendering the fan useless.
2. Real possibility of a water trap developing in the duct over time.

Much better to install ducting which is solid walled, insulated, always rising, and exits the roof through a vent tile.

mikeysmith

MicktheMan wrote: »

Imo, yes it is a bad idea to duct a fan out through the soffit for a couple of reasons;
1. Huge reduction in fan capacity depending on duct length & type to the point of rendering the fan useless.
2. Real possibility of a water trap developing in the duct over time.

Much better to install ducting which is solid walled, insulated, always rising, and exits the roof through a vent tile.

you can fit the inline fan close to the bathroom and slope the ducting down to soffit on a plank of timber, shouldn't be any water traps.

i work in a related technology field and it was always my understanding that mechanical extraction out through the roof was the best way alright

Alkers

MicktheMan wrote:

Imo, yes it is a bad idea to duct a fan out through the soffit for a couple of reasons; 1. Huge reduction in fan capacity depending on duct length & type to the point of rendering the fan useless. 2. Real possibility of a water trap developing in the duct over time.

Can you expand on why this is the case?

MicktheMan

Simona1986 wrote: »

Can you expand on why this is the case?

Which point?

Alkers

Why the fan capacity is reduced do much

MicktheMan

The duct is a resistance to air movement. How much of a resistance depends on a number or characteristics;
1. Length (the longer the bigger resistance)
2. Type (flexible ducting creates turbulence in the airflow increasing the resistance)
3. Restrictions (exposed, uninsulated flexible ducting often has a build up of water in the ducting reducing the effective duct area creating back pressure and eventually closing of the ducting completely)

mikeysmith

Which end of the duct should the fan go?

Alkers

MicktheMan wrote: »

The duct is a resistance to air movement. How much of a resistance depends on a number or characteristics;
1. Length (the longer the bigger resistance)
2. Type (flexible ducting creates turbulence in the airflow increasing the resistance)
3. Restrictions (exposed, uninsulated flexible ducting often has a build up of water in the ducting reducing the effective duct area creating back pressure and eventually closing of the ducting completely)

In our case, we have the extractor mounted in the ceiling with less than a 1m run of ducting in the attic to the soffit. The duct run would only be marginaly shorter if we were to instead vent through a roof tile.

Does the ducting type differ if using a roof tile?

Would having a vertical run of ducting opening onto the roof not be more likely to fill with water than one which opens onto a soffit?

MicktheMan

Simona1986 wrote: »

1. Does the ducting type differ if using a roof tile?

2. Would having a vertical run of ducting opening onto the roof not be more likely to fill with water than one which opens onto a soffit?

1.It shouldn't. Ducting should have a smooth internal surface, with as few bends as possible i.e. as least resistance to the airflow as possible.
2. How? Any water condensate would run back down the duct into the internal space thus alerting the occupant to an issue with the duct insulation.

mikeysmith

Is it a big job to get an outlet fitted to a existing tiled roof ?

I would presume it is?
I've seen them on slate type roofs

MicktheMan

mikeysmith wrote: »

Is it a big job to get an outlet fitted to a existing tiled roof ?

No, once you have safe access onto the roof.

mikeysmith

Does it matter what type of vents you use

https://www.amazon.co.uk/gp/aw/d/B004X4S722/ref=mp_s_a_1_1?ie=UTF8&qid=1513118977&sr=1-1&pi=AC_SX236_SY340_FMwebp_QL65&keywords=bathroom+ceiling+vent

The above type seems specific for the task but is it any better than a grill type vent?

Phil.x

Why don't you want to go through the wall?

Alkers

yabadabado wrote:

I was g

MicktheMan wrote:

1.It shouldn't. Ducting should have a smooth internal surface, with as few bends as possible i.e. as least resistance to the airflow as possible. 2. How? Any water condensate would run back down the duct into the internal space thus alerting the occupant to an issue with the duct insulation.

I meant more that rainwater would get in the vent and run down to the fan?

We have a soffit fan because the soffit is low enough on the external wall so if we mounted the fan on the back wall, it could only be at shoulder height or below. If I can source an appropriate vent tile, I'd consider re-routing it alright.

If the losses are as bad you say they are, I can see a lot of kitchen extracts being affected also?

mikeysmith

Phil.x wrote: »

Why don't you want to go through the wall?

Same distance
Less work
Less chance of gable wind blowing against fan