And how many hours should I wait? This is a medium-sized attic (whatever that means).

Hmmm... You should not really need to wait, unless the fan is really much too small. It really wants to be sealed into the opening. I worry about the cat...

12 minutes ago, Redbeard said:

Hmmm... You should not really need to wait, unless the fan is really much too small. It really wants to be sealed into the opening. I worry about the cat...

Oh, the cat is not in the house right now - she's at my girlfriend's.

 

OK, second try: 

 

Is that enough? The fan is 30W - is that ridiculously weak?

So what results are you getiing?

17 minutes ago, Garald said:

Is that enough? The fan is 30W - is that ridiculously weak?

 

Afraid so. 

 

The one I used was about 750W at a guesstimate. I had it sealed in the sash of a window with airtightness tape in a sheet of OSB. Proper tight. 

 

It would really stick doors closed. Even with that I still needed a candle flame to detect the smallest leaks. 

 

 

 

 

Edited December 4, 20232 yr by Iceverge

21 minutes ago, ProDave said:

So what results are you getiing?

 

Couldn't detect a thing. But then, as people are saying, 30W is probably just too weak. The patchouli stick indicated that air was being sucked out of the room only when it was in the immediate vicinity of the fan.

 

Is there such a thing as a powerful fan the size of a cat?

One alternative is just to give up on the fan approach and just do the wet-hand approach on a very cold day. Today it's just 9C, but the other day it was about 0C, and the fact that air gets through the perimeter of an outside metal door in the ground floor was obvious (it isn't today).

PS. It may be that there are just no gaps left in the attic - at least no gaps a young wasp can get through. Up to a couple of weeks ago, wasps were getting through and then getting stuck and dying in the attic. Turned out the joint between a ceiling beam and a side wall had not been sealed. The contractor found the problem (after I insisted repeatedly that a problem existed), applied sealant (polyurethane - is it OK that it's unsealed?) and told me to tell him if I noticed anything of the sort still happening.  There have been no more dead wasps since.

25 minutes ago, Garald said:

 

Couldn't detect a thing. But then, as people are saying, 30W is probably just too weak. The patchouli stick indicated that air was being sucked out of the room only when it was in the immediate vicinity of the fan.

 

Is there such a thing as a powerful fan the size of a cat?

This was what I used, an old office fan, not very powerful

 

 

With that sucking air out of the house, I could go around looking for leaks.

 

The house was pretty air tight, the telling thing, when the fan had been on for a couple of minutes, go and open a window and there was a big whoosh of air entering back into  the depressurised house.

1 hour ago, ProDave said:

 

 

The house was pretty air tight, the telling thing, when the fan had been on for a couple of minutes, go and open a window and there was a big whoosh of air entering back into  the depressurised house.

 

Hm. No whoosh. Well, maybe some whoosh when I open the big window in the little staircase leading to the attic from the cat door, but no whoosh whatsoever when I open a skylight.