Should I increase the size of My opening

[outerlimits]

I Just finished my first IB install this weekend. It is two FI 18's threw the floor joists in a crawl space. I was trying to cut the opening to sizes of the floor to match vent sizes I came across on line. I found a site that stocks vents in even sizes 10x10 ,10x12, 10x14 and so on. I cut the opening to fit a 10x12 vent opening. I was planning on enlarging it as needed. So my question is what are some signs that my opening is to small and I would get more out put with a larger opening? In general would you think that a 10x12 opening would be to small, also I was just thinking that the slots in the grate would also close down the opening area.

I know this has to have been discussed before but I couldn't come up with anything in detail using the search. So any info on this topic would be greatly appreciated.

Thank you
Jake

[ThomasW]

Not much to discuss other than to say when the opening is too small the IB performance is sub optimal.

To small and some output is running into a dead end then interfering with the direct output in line with the opening.

Per FAQ #15 the opening for your IB should be 12" X 18".