Polskasweetie wrote:
Hello all, and i do apologise in advance if this has been asked before,
but have no reliable people to turn to here for this.

Currently have an Airflow Loovent Eco 100mm extractor fan in the kitchen,
that stopped working a few days ago. Looking around, and in consideration
of the square hole the existing fan will leave when replaced, I am
thinking of replacing it with the Airflow QuietAir QT150B.

There isn't a square hole - there's a 100mm circular hole. The unit is
screwed to the wall/ceiling outside of that area - that may leave a
square-ish part where the paint finish differs if the area has been painted
since the unit was fitted.

1) is it safe / ok to replace with a bigger fan, or do i have to stick
with a 100mm fan as a replacement?

A 150mm unit will need a 150mm hole. Whether you can cut that depends on
what the hole is in. Don't forget there may be a duct behind it, so it's
not just cutting the ceiling but you'd also need to upgrade the duct and
exhaust vent as well. Unless there's a good reason to get a bigger fan
(airflow, noise?) it wouldn't be worthwhile, IMHO.

2) Read in the forums about centrifugal etc. I know the Loovent is
centrifugal, but the QuietAir is "axial high efficiency impeller" (from
the description). Do i stick with another cntrifugal model, or can i
switch to this axial one?

Centifugal means the air comes into the unit from the sides, axial means it
comes in from below (assuming the unit is ceiling mounted). Axial means you
can see into the fan from below, not for centrifugal. Which is best depends
where the vapour you're trying to extract is coming from.

Theo