Paul Novus MVHR Fan Bearing Replacement

Woke up to a vague, persistent ‘mechanical’ noise somewhere in the house. After opening the door to the Plant Room it was immediately apparent the fan bearings on the Paul Novus 450 MVHR unit had failed – slightly surprising after only 6 years, but then they are running 24×7. The fans were still working and there were no errors on the control panel, but the noise wasn’t good – and I have enough experience with bearings to know they only ever get worse, not better. What was good was the sound attenuation on the MVHR ducts – the noise was only really obvious in the Plant Room and in Bedroom 2 immediately beneath it, so the noise was not being transmitted to other rooms via the ducting.

A quick Google search turned up the service manual for the Paul Novus with guidance on getting to the fans and the advice to replace the complete fan units: centrifugal housing, fan rotor, motor, electronics etc. (Estimated cost of £280 per fan.) I was hopeful it would be possible to just replace the bearings instead and proceeded with some dismantling.

I was very pleasantly surprised by the specification of the fans: embpapst units with part number G3G160-AD54-22. Really good build quality and the prospect of not being too difficult to repair. YouTube turned up an excellent video showing the dismantling and bearing replacement procedure.

Bearings are generally standard and pretty cheap and one of the great things about living in Derby, with its rich heritage of railway and aerospace engineering, is that there are some excellent suppliers of these sorts of spare parts located within a few miles. Derby Bearings Ltd don’t win any prizes for inventive business naming but they do offer an excellent service and carry good stocks – they had a couple of options in the correct size for only £4 each (£8 per fan).

The fans are now running quietly again and peace is restored. I’ve written a Technical Article with some hints and tips to make the job easier next time – or for other people attempting it for the first time.

I do wonder if the exceptionally hot summer weather contributed to the premature failure – could the heat have softened the lubricating grease in the bearings, causing it to leak out, making them more prone to rusting when the cold and damp weather returned?

MVHR Running Costs

There are modest costs associated with running an MVHR system. Since the fans run 24×7 they typically use more electricity than intermittent-use extract fans in bathrooms and kitchens. There are also filters that need to be replaced on a regular basis.

I think these MVHR running costs should be treated as part of the heating costs, since they’re a natural consequence of the energy efficiency measures that reduce the heating bills.

First the filters: For a PAUL Novus (the 300 and 450 take the same filters) a set of genuine PAUL replacement filters consisting of one G4 and one F7 filter cost around £30 plus VAT from the Green Building Store. These need changing 2 – 3 times per year so that’s roughly £100 per year. Aftermarket filters are available from other suppliers such as but those don’t appear to be significantly cheaper.

The electricity usage varies depending on how much the Boost setting is used and also on how blocked the filters are (assuming the MVHR unit has fans which compensate for filter blockage by running faster, consuming more power, like the PAUL Novus does). Without Boost (i.e. on Level 2) I’m seeing around 0.9 kWh per day or about 26 kWh per month. Allowing for some running on Boost (i.e. Level 3) that’s roughly £50 per year.

All in, that’s about £150 per year.

How do I know how much electricity the MVHR unit uses? There’s a sub-meter in the consumer unit on the circuit dedicated to the MVHR – similar to the one shown below. These are £10 – £15 on eBay and are a good way of keeping a watch on the running costs.

DDS238-1 DIN-Rail mounting kWh meter