MVHR Installation - No Such Thing as Good Vibrations
By Andrew Nash, Residential Business Development Manager, December 2014
Recently, I’ve visited a number of apartments where transmission of vibration from wall-mounted MVHR units to adjacent rooms had been reported. The problem in all cases was not really the wall-mounted MVHR unit but the structure to which it was fixed!
I think we should draw a distinction here, between a wall and a partition. Walls, to my mind, are made of concrete, bricks or blocks. They have mortar joints. They have mass. A 13mm plywood sheet supported on a lightweight steel frame faced on both sides with 15mm plasterboard is a partition, not a wall. That's what MVHR units in modern apartments are being hung on.
It's safe to say that no ventilation product will ever be completely vibration free and that wall-mounted MVHR units were designed to be fixed to walls. One manufacturer’s installation guide I read gave a minimum requirement of 200kg/sq.m for the supporting structure. That would mean either a brick or a concrete wall. Light-weight partition walls simply don't have the mass to absorb even the smallest amount of vibration.
To put current installation practices in perspective, what designers and installers are currently doing is rigidly fixing ventilation plant directly to the back of a light, flexible partition and then being surprised when it can be felt from the other side! Both the mass and flexibility of wall materials have an effect on vibration transfer. Brick walls have high mass and don’t flex. 13mm plywood has relatively low mass and flexes a lot.
A 19mm plywood cupboard back-board should be regarded as the minimum requirement. 22mm MDF is stiffer and has far greater mass. 25mm MDF would be even better, having around twice the mass of an equivalent area of 19mm plywood.
Whilst a heavier, more rigid back-board reduces vibration transfer, the single biggest improvement can be gained from the rear of the services cupboard being mounted on an independent studwork frame. This prevents any vibration from being transmitted directly through the structure to adjacent rooms and frankly should become the standard construction method in modern apartments.
For our part, we have developed anti-vibration mounting kits for our MVHR units. These use flexible rubber Anti-Vibration Mounts to isolate the unit from the supporting structure. Using a flexible mount arrangement on a solid independent structure gives good predictable results, eliminating all vibration transfer.