Sealing around extractor fan

[Newowner3019!]

Hi everyone, I've tried to read as many past comments on this as possible, but am struggling to find a definite answer!

Long story short I installed new ducting for a kitchen extractor fan. There is a small gap around the edges that needs to be filled to stop warm air getting into the loft (it's a bungalow).

Should I use decorators caulk or silicone/bathroom sealant?

I have no intention of painting over the gap (as the kitchen was recent painted and I'm not fussed about hiding the join), but that's not to say it won't be repainted in the very distant future.

Any advice on brands of sealant/caulk to use would be appreciated. Thanks!

 

[JohnD]

Go into the loft and pack loft insulation round the duct where it passes through the ceiling. This will block airflow. The quilt can be stuffed tightly into gaps. Wrapping the duct in insulation will also reduce the risk of condensation in it.

In the kitchen, silicone will be more flexible and durable long term. Caulk tends to shrink and crack.

You could use expanding foam in the loft, which will cement it into place, but seal the kitchen side first, or the foam will ooze through and be very difficult to clean off.

 

[opps]

In the kitchen, silicone will be more flexible and durable long term. Caulk tends to shrink and crack.

Whilst true that caulk will shrink, silicone will repel paints. As a decorator, I would recommend a MS polymer such as CT1. It can be overpainted as and when required and is almost as flexible as silicone.

 

[aveatry]

Just as a side note you would of been much better for airflow if you carried on with round tube in the loft instead of converting to a flat one from what I am seeing. - I am guessing that there is another conversion back to a round one at the external outlet vent. Also rigid duct is far better than the flexible stuff. Sometimes people have to use flex or the flat channel but it looks like you have the perfect opportunity to keep it rigid round all the way.

 

[JohnD]

The rigid duct can also be tilted fractionally as it runs through a loft, so that (after the initial warm rise) any condensation runs towards the vent and drips outside the house.

 

[foxhole]

Box it in, easier to seal and will look better. Flexi should’ve been reduced to the shortest length as that will collect a lot of grease.

 

[JohnD]

Box it in, easier to seal and will look better. Flexi should’ve been reduced to the shortest length as that will collect a lot of grease.

Or a simple piece of rigid duct would have been better.

 

[Newowner3019!]

Thanks everyone for your replies. Perhaps the attached BEFORE and AFTER photos will explain why I have made the ducting choices I have. I upgraded it from a 100mm bodge to a 150mm (or 22x90mm rectangle) duct.

In short, I had to covert round to flat to fit through the joists in the loft. I used semi-rigid ducting instead of flexible or rigid as a balance between flexibility and smoothness.

As for the original question, seems like CT1 is the way to go. I have already packed with insulation from the top already, so will just seal it from below now.

Thanks again for your replies

 

[Newowner3019!]

Go into the loft and pack loft insulation round the duct where it passes through the ceiling. This will block airflow. The quilt can be stuffed tightly into gaps. Wrapping the duct in insulation will also reduce the risk of condensation in it.

In the kitchen, silicone will be more flexible and durable long term. Caulk tends to shrink and crack.

You could use expanding foam in the loft, which will cement it into place, but seal the kitchen side first, or the foam will ooze through and be very difficult to clean off.

Whilst true that caulk will shrink, silicone will repel paints. As a decorator, I would recommend a MS polymer such as CT1. It can be overpainted as and when required and is almost as flexible as silicone.

Just as a side note you would of been much better for airflow if you carried on with round tube in the loft instead of converting to a flat one from what I am seeing. - I am guessing that there is another conversion back to a round one at the external outlet vent. Also rigid duct is far better than the flexible stuff. Sometimes people have to use flex or the flat channel but it looks like you have the perfect opportunity to keep it rigid round all the way.

The rigid duct can also be tilted fractionally as it runs through a loft, so that (after the initial warm rise) any condensation runs towards the vent and drips outside the house.

Box it in, easier to seal and will look better. Flexi should’ve been reduced to the shortest length as that will collect a lot of grease.

Or a simple piece of rigid duct would have been better.

Thanks everyone I've put a response in my comment above (I forgot it add the quotes in my original reply)

 

[aveatry]

Thanks everyone for your replies. Perhaps the attached BEFORE and AFTER photos will explain why I have made the ducting choices I have. I upgraded it from a 100mm bodge to a 150mm (or 22x90mm rectangle) duct.

In short, I had to covert round to flat to fit through the joists in the loft. I used semi-rigid ducting instead of flexible or rigid as a balance between flexibility and smoothness.

As for the original question, seems like CT1 is the way to go. I have already packed with insulation from the top already, so will just seal it from below now.

Thanks again for your replies

Ahh that explains a lot and its way better than before. Just thinking on the joist arrangement - they are very close together and I wonder if you could of treated it like when you cut in a loft hatch and double up the sides --- whatever its called so you could carry on with the 150 round without going narrow.
And i might be inclined to get a box stainless cover all the way up. like this but you dont have to spend that much
But I still think you could of done it in rigid in the attic with the round. But at least its accessable for cleaning - I had flat trappen withing the ceiling and when I took the celling down to do a refurbish it was a right state inside the ducting but I now have it so I can get to it and changed to round.