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MVHR: More extracts than supplies?


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Can't put this off any longer, decision time!

I've had the MVHR unit fired up and it's disappointingly noisy. Of course this is without any structural isolation, and without any ducting on the house side of things. Hopefully that will quieten things down, and if not my next step is an attentuator in the supply duct, I think.

 

The noise has made me reconsider where I should put the vents. So my new plan is:

One extract above the shower (as previous plan)

One extract at high level in the kitchen/lounge space

One supply above the front door

 

If the noise proves acceptable, I would like to add a second supply above the bed, so this gives two pairs which should be easier to balance.

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Sorry to hear (no pun intended) about your noise issues Crofter. This has got me worried about my planned MVHR installation now. May I ask you to elaborate on what the issues are? Given your proposal to move vents I take it this means that the noise is coming from these, or have you not actually got as far as siting any vents yet?

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7 minutes ago, MJNewton said:

Sorry to hear (no pun intended) about your noise issues Crofter. This has got me worried about my planned MVHR installation now. May I ask you to elaborate on what the issues are? Given your proposal to move vents I take it this means that the noise is coming from these, or have you not actually got as far as siting any vents yet?

 

Yes I've not actually sited any vents yet. I'm hearing a fair bit of fan noise from the unit, and a lot of this seems to come from the inlet/outlet spigots. Hopefully a few metres of ducting will help calm things down.

It was a fairly cheap unit and I can't say I'm overly impressed, so far. Sometimes you get what you pay for!

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1 hour ago, Crofter said:


Yes I've not actually sited any vents yet. I'm hearing a fair bit of fan noise from the unit, and a lot of this seems to come from the inlet/outlet spigots. Hopefully a few metres of ducting will help calm things down.

 

Ah I see. Finger's crossed it is primarily the fact that it is running unpiped. I am sure that others that have installed MVHR units have run them prior to installation (I know I will be - I won't be able to help but fire it up!) and so should be able to comment about this.

 

I see that inline silencers/attenuators only cost tens of pounds and so that could be worthwhile as a matter of course anyway.

 

What unit have you got?

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41 minutes ago, MJNewton said:

 

Ah I see. Finger's crossed it is primarily the fact that it is running unpiped. I am sure that others that have installed MVHR units have run them prior to installation (I know I will be - I won't be able to help but fire it up!) and so should be able to comment about this.

 

I see that inline silencers/attenuators only cost tens of pounds and so that could be worthwhile as a matter of course anyway.

 

What unit have you got?

My unit came from an outfit called 'Boulder'- definitely at the budget end! It was really the only way that I could get the features that I needed (summer bypass) within budget.

I suppose if it turns out to be a disaster, the unit itself could be swapped out for a better one quite easily, but let's hope it doesn't come to that.

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I'd not worry too much about noise coming direct from the big ducts as ours was noisy when I tested it like that.  I found silencers (home made) made a tremendous difference to the noise level once everything was installed, and our MVHR can be noisier than most because of the built in air-to-air heat pump.  I doubt that any MVHR could be any noisier internally than ours with the heat pump running TBH, yet it's pretty silent with the silencers and ducting fitted.

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  • 4 weeks later...

MVHR is now temporarily installed for testing (and to let me use the shower!)

I've suspended the unit using rope, not ideal perhaps but it was quick and easy to get me up and running.

Only one extract (above the shower) and one supply (at the front door, about as far from the extract as possible). I'll add second extract at high level in the kitchen/lounge.

The unit was supplied with the cheap and nasty flexible insulated ducting. I'm using this at the moment but could swap it out later. All of the runs are within the loft space so easy to access.

 

Everything appears to be working well, but it is pretty noisy. I've bought two in line attenuators which didn't seem to make much of a difference. Most of what I can hear is from the extract, all I've now set it up with both attenuators in this duct. The only way I can get the noise down to a reasonable level is to open up the supply vent all the way- it gives a whooshing sound when partially closed down, presumably as the airflow accelerates through the reduced gap.

 

So...

Are better quality vent terminals available that will reduce the noise?

What's the best position for attenuators- close to the unit, or closer to the terminal?

What effect will duct length have? The unit is oversized for the house and could easily handle longer runs.

The ducting and terminals are only 100mm. Maybe I should double up, or switch to larger ducting, to reduce velocity and therefore noise?

What sort of arrangements have people come up with for DIY attenuators?

 

Thanks

 

 

 

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31 minutes ago, dpmiller said:

how high are the fans turned up?

There's low, medium, and high settings. Noise at low is still quite bad.

I'll see if I can get a reading using a decibel meter app. I'd say it's approximately the same as a fridge though, so around 38-40dB.

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but is each setting not variable also? Noise is pretty much dependant on flow and it's best to slow the fan rather than close over the terminal. Have you done any flow tests to see of you're in the right ballpark?

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10 hours ago, Crofter said:

Most of what I can hear is from the extract, all I've now set it up with both attenuators in this duct. The only way I can get the noise down to a reasonable level is to open up the supply vent all the way- it gives a whooshing sound when partially closed down, presumably as the airflow accelerates through the reduced gap.

 

I'm a bit confused about this bit. Whilst supply and extract complement each other functionally they nevertheless operate completely independently with their own fan and air ways. I would therefore not expect adhustment of a supply vent to change the noise levels heard from an extract vent. 

 

Perhaps though, the fact this is happening is a big clue as to what the issue might be? (Not sure what though!) 

 

Incidentally, have I understood you correctly that there is only a single supply and extract vent at the moment? If so, it could well be that the minimum speed of the unit is still far exceeding the airflow that you want/need passing through the vents. An anemometer would be useful, and will be required anyway come balancing time. 

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56 minutes ago, MJNewton said:

Incidentally, have I understood you correctly that there is only a single supply and extract vent at the moment? If so, it could well be that the minimum speed of the unit is still far exceeding the airflow that you want/need passing through the vents. 

 

This was my first guess.

 

Depending on the model, you should be able to change the fan speed for each setting, as @dpmiller said.

 

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Thanks for the replies. I haven't made any real effort to balance the system yet, but the unit does seem inherently quite loud even with no ducts connected.

I'm not aware of any facility to alter the fan speeds other than the basic high/med/low- but worth investigating.

Most of the noise seems to be from the extract vent, rather than from the supply or vibration from the unit.

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Just had a read at the MIs for the Boulder units and it's pretty useless. Looks like the LCD controller has a "fan speed" button and "up-down" buttons; however the data sheet quotes fixed flows for each speed.

You might be out of luck. Which model is it and how well matched to your requirements is it?

 

You might try a restrictor ring where the duct attaches to the unit.

 

But without an anaemometer we're all guessing...

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