Today I drilled the hole for our mechanical ventilation with heat recovery unit.  Quite a scary drill but it went without any serious problems.  My biggest fear was that the drill would “kick” really hard if it suddenly jammed but the drill had an automatic clutch so it would disengage whenever the drill got stuck.  It still kicks a bit, but not too hard.

I drilled from the inside and I was pleasantly surprised at how clean the exit hole was.

This isn’t installed properly yet - I was just positioning the unit to make sure it fits.  Plus the unit is missing the front grill.

I’ve been keeping notes on installing MVHRs on the Navitron Wikihttp://www.navitron.org.uk/pmwiki/pmwiki.php?n=Ventilation.MechanicalVentilationWithHeatRecovery