Acoustic Isolation of MVHR Unit

[MJNewton]

I am considering options for mounting a Xpelair Natural Air 180 MVHR unit on the block wall inside the loft space with particular regards for vibration-transmitted acoustic isolation.

 

Firstly, I should ask if others do consider it necessary to even be thinking about this? If it is, any recommendations on the best approach to take? The unit is ~20kg and not only has rear mounting holes but also some on the side that are intended to be used if installing in a kitchen cupboard.

 

I am contemplating using a couple of gallows-style wall brackets from which the unit could hang on springs attached to battens on the side of the unit. I figure this would isolate it well in terms of vibration transmission whilst still being within the range of movement that could be accommodated by short flexible ducting lengths mating to the rest of the system. One difficulty with this approach is knowing what springs to buy as all the ones I see online have absolutely no information useful for me to apply Hooke's Law that I had much practice with at school!

 

Any comments/suggestions?

Edited April 7, 2018 by MJNewton

[Crofter]

I've recently been looking into this myself. I think @JSHarris will have some useful insights.

 

One approach is to hang the unit using four threaded rods. These pass through a short tubular rubber mount (like an engine mount) and then a washer and nut go on top of the rod. So all the weight is carried by the rubber, but if the rubber were to fail for any reason the unit cannot fall any distance.

[Jeremy Harris]

I fitted ours on a timber base supported on four old-style Mini exhaust mounting bobbins, like this:

 

 

Seems to work very well, and our MVHR produces a lot more vibration than many, as it has an integral air-to-air heat pump built in, so is pretty heavy (around 70 kg).

[joe90]

Yes I also used rubber type engine mounts but I also hung it from the roof timbers rather than fixed to the loft floor so no noise ( if any) could be transmitted down into the bedrooms. On another thread regarding sound deadening of soil pipes I remember it being said that concrete or “mass” was good at sound deadening so hanging from a concrete wall would be good I would have thought.

[MJNewton]

Thanks everyone for the replies. I did spot some isolation hangers like the following:

 

 

..but they seemed surprisingly pricey and not all that readily available. I'll look to make a DIY equivalent with whatever I can lay my hands on, perhaps exhaust hangers as some have mentioned.

 

For isolating the unit from the ductwork I believe semi-rigid aluminium ducting like that below is what's generally used and so presumably is flexible enough to perform this function well?

 

 

Is there any issue siting this so that it acts as right-angle bend between the MVHR unit and the ducting? Or am I better using a solid (smooth) right-angle bend and then using a short length of the semi-rigid to connect straight with the ducting? I might be over-thinking things and it really doesn't matter either way...

[Jeremy Harris]

I used the same semi-rigid in short lengths from the MVHR and  found it easy to use and it also doesn't seem to transmit vibration.  The very flexible stuff with the wire to keep it roughly round isn't great, IMHO, as it tends to have a pretty high flow resistance, which isn't good for overall efficiency.  The semi-rigid stuff seems a heck of a lot better in this regard.

[MJNewton]

Great - thank you.

[epsilonGreedy]

On 4/8/2018 at 07:35, joe90 said:

Yes I also used rubber type engine mounts but I also hung it from the roof timbers rather than fixed to the loft floor so no noise ( if any) could be transmitted down into the bedrooms. On another thread regarding sound deadening of soil pipes I remember it being said that concrete or “mass” was good at sound deadening so hanging from a concrete wall would be good I would have thought.

 

 

I heard similar advice at the NEC show this year i.e. if trying to minimize noise then mount from a vertical surface instead of floor platform. Hanging off rafters sounds like the same concept taken further.

[lizzie]

Mine is hanging from the wall in the plant room (no roof space in my house).  It has only been run for an hour or so pre commissioning but it seems very quiet...........when it was running I heard distant rumbling (I was at the other end of the house) I thought that it was MVHR rumbling  and got worried, went to find out about noise and was pointed at the digger working outside LOL Gave them all a good laugh!