Help with ventilation in guest toilet

[Josterman]

Hello,

We are renovating a guest WC and planning to install an exhaust duct and a bathroom fan for better air quality.

The guest WC is located on the ground floor, not adjacent to an exterior wall, so the duct is planned to be routed up through the insulated joist space and up into the cold attic. (In about 1-2 years, the attic will be insulated and the duct will be extended out to the roof.)

I plan to run a 100mm spiral duct through the joist space and set a 90-degree bend that comes out through the wallboard where the fan connects. Is this correct? How should I connect it? Should the spiral duct be connected to some sort of fitting or clamp to hold it in place, or can it just poke up temporarily?

Then, during the winter months, how can condensation be avoided? Styrofoam box, insulation in the duct, or is it just a matter of turning off the fan and sealing the duct until we have completed the insulation?

 

[Centano]

Is the idea that you should release the air in the attic for 1-2 years, or am I misunderstanding something?

 

[Josterman]

Is the idea that you will release the air into the cold attic for 1-2 years or am I misunderstanding something?

Yes, if that's possible!? It's a large, well-ventilated attic. But if it releases too much condensation, we'll have to vent it out through the roof sooner than that.

 

[Dr Benz]

You do not want to add humid indoor air to the attic. It should go out directly. It can be difficult enough to keep the attic free from moisture as it is.

 

[Centano]

Since it is a cold attic, it is asking for trouble if you release warm moist air there. If you have planned to vent through the roof, do it now and don't wait several years.

 

[Josterman]

Thank you, I hear what you're saying. I won't wait to drag it out onto the roof.. Do you have any advice on my other questions?

 

[Dr Benz]

I can't answer for the exact right connection, but I would have mounted it directly to the ceiling. Now you've already made a hole, but I don't understand why you should go through the wall.

I have both the bathroom and toilet uninsulated so far because I haven't had the time/prioritized it. I've seen the occasional drop in the pipe so far but nothing more. However, I live in Skåne with a mild winter. So it depends a bit on where you live. But I would say that you'd rather have the fan running for a good indoor climate. It should always be on. Then keep an eye out if you start seeing condensation. But I would recommend insulating it while you’re installing the pipes.

 

[Utsliten och utdömd]

Best to install an inline fan in the attic.
Regular bathroom fans are not designed for long ducts/back pressure.