Isolate vibration from bathroom extractor sited in loft

[grimep]

As per the title. There's an extractor fan in the loft above the bathroom. At the moment it is vibration isolated using a Heath Robinson solution with it screwed down to a board with foam glued in a sandwich with a lower board which is screwed to a rafter.
The only solid thing to attach it to is the wooden roof trusses/ joists.
I need to move it so it's higher up to make room for thicker insulation, but don't know of a product or method of fixing it in place so that vibration is minimised. Screwing it directly to a truss would cause noise and vibration throughout the house. This must be something that's been solved many times over, how do other people do it??

 

[pcaouolte]

Usually with a Heath Robinson approach like yours a piece of plywood with some carpet underlay between the ply and the truss and another piece of carpet underlay between the fan and the ply. Hopefully someone else will come along with a less crude setup.

 

[foxhole]

I hung mine from rafter on a couple of springs , very little vibrations transmitted back to timber .

 

[jacko555]

Bungee cords

 

[grimep]

Heh, after writing this I sketched a little contraption with bunjees cords, oh well, Heath Robinson it is then.

Could be a Dragons Den product idea in here somewhere

 

[Harry Bloomfield]

Bungee cords, inner tubes cut up into rings, car exhaust rubber O's what ever they are called.

 

[JohnD]

Do you know the make, model and age?

Some good quality modern ones are very quiet

 

[cdbe]

I'm watching with interest. Ours in in the loft right above the bed.

 

[RandomGrinch]

For a comparison, I regularly play with vacuum pumps in laboratories.
They are far noisier and vibrate more than an in-line bathroom fan.
To give you an idea of the vibration isolation we use, a web search gets you these sort of things:

vacuum pump vibration isolation - Google Search

The general idea is to decouple the pump from the frame with rubber/foam/springs/air, or a combination of them.

As has been stated above, a 'Heath Robinson' contraption will do exactly the same job, for a lot less money

 

[Deleted member 174758]

Our bathroom extractor is a Heath Robinson contraption, too, fixed to the wall. In our case. It is now fixed to a piece of plywood through rubber feet, and the plywood has rubber feet through which it is fixed to the wall using frame fixings
The fan is connecter to the rigid ductwork at each end through short lengths of the flexible hose that came with our last but one tumble dryer so that vibration can't be transmitted to the ductwork. It's up in the eaves, where it won't ever be seen, so fancy workmanship isn't required (made with military prevision to the RAF standard - or Rough As Flip...)

 

[grimep]

Damn, I chucked an inner tube away on Saturday, should've read this first!

 

[Old Salt]

Do a search on ebay for rubber pump mountings. Lots of options come up that could either mount to your fan direct or some form of base depending on the fixings.

 

[Justin Passing]

There is some tech behind it... here's some you'd consider for a more demanding situation so you can see what I'm on about:
Mass is important in anti-vibration.
If using rubber, the type of rubber is important.
Calculations revolve around coupling, cutoff frequencies, characteristic resonances and hysteresis losses.
If say you're sitting a fan/pump on the joists, you need to reduce the amount the fan/pump moves, so fix it to a paving slab to increase the mass, so it moves less. A padstone is more dense but more cost per kg.
Then the support between that and the joists needs to be as squishy as possible - ideally something like an air bag, so the coupling of the movement to the joist is as weak as possible. Air bags are rarely practical, but are used where they can be maintained. (e.g. a whole tyre inner tube, partially inflated). You can use a lot of soft metal springs, but they aren't very lossy.
Increasing the mass increases the coupling, but there are square laws etc in there so mass increase is still good - you need more spreading of support- intuitive, really.
Ordinary rubber doesn't have much hysteresis - in other words the energy you put in to squash it is stored, and is given back when you release. No good. Something like Sorbothane (see ebay) is designed to not do that, but heat up slightly to absorb the energy. It's used on optical equipment etc. You need to look at their tables to pick the right shape/volume of foot for the mass and frequency (rpm for a fan).
I've used that in other circumstances.

Salamander and Manrose and Stuart Turner sell or recommend particular feet, but they aren't great, I've tried that.
Bungees off the rafters would be pretty good, until the rubber in them perishes. Haven't tried that.

Rolls of old carpet aren't bad as long as there's enough of it. I've used that. It tends to settle into a hardish lump. Cheap pipe insulation lasts a week... ditto!
Non-rotting foams like Dunlopillow aren't bad. I've used that.

Ideally, a bit of something like old shelf - melamine faced chip board, to sit the fan on with a brick, 3 or 4 of those Sorbothane feet on to another bit of old shelf resting across rafters, and you have negligible structural transmission, the stuff is that good. You might still hear the motor of course.

 

[cdbe]

Damn, I chucked an inner tube away on Saturday, should've read this first!

I keep telling my wife, the minute after I throw away something that's been cluttering up my garage for years, I will find a use for it.

 

[JohnD]

@grimep

Do you know the make, model and age?

Some good quality modern ones are very quiet