Magnuss may not be a household name in bathroom extractors, but they’re stocked by a mid-size builder’s merchant near PEATA HQ. It’s a fairly standard 100mm extractor fan, and comes in a kit with a short piece of duct and a gravity vent. That’s everything you need to install it through an external cavity wall. It’s described on the packaging as capable of 22 l/s, so ample for a bathroom. When we put it on the test rig without the gravity vent, the minimum benchmark method flow rate test reports just under 16 l/s on our test rig. This isn’t great, but is good enough to satisfy the building inspector. However, it’s mandatory to have some form of backdraft preventer when it’s installed. Once we put the supplied gravity vent on it, this drops all the way to 11 l/s. This flow rate is a big FAIL for Part F. Again, we’re seeing that fans which look OK on the packaging are actually not compliant with building regs once installed. Do your flow rate tests to be sure!
We’ve written to Magnuss, and will let you know how they respond.