Undersink heater, when is expansion vessel needed?

[jat147]

Hi, We've got a small industrial unit and need hot water for 2 sinks so have got a Hyco speedflow 10L unvented heater. The instructions mention that if the nearest draw off for cold water is less than 2.8m away then no extra parts are needed, but that an expansion vessel & check valve is needed for other installations.
Sorry if I'm being thick, but an Undersink heater will always have a tap nearby, wont it? It goes on to add that an expansion vessel and check valve are needed to stop hot water expanding into the cold supply.... OR that an expansion vessel & pressure reduce valve are needed to stop the pressure relief valve leaking constantly.
Question is, is it wise to fit the unit under the sink and look for the 2 above problems to appear before deciding if we'll need the extras or not?
many thanks in advance.

 

[matt1e]

The instructions mention that if the nearest draw off for cold water is less than 2.8m away then no extra parts are needed, but that an expansion vessel & check valve is needed for other installations.

Question is, is it wise to fit the unit under the sink and look for the 2 above problems to appear before deciding if we'll need the extras or not?
many thanks in advance.

You are reading it wrong.
If the nearest cold water draw off Is more than 2.8 metres away than no extra parts are needed.
You are going to need a expansion vessel and check valve if you are going to put the unit under the sink, you will also req a pressure reducer if the cold pressure is more than 4.2 bar

Matt

 

[jat147]

Thanks Matt, that does more sense now I'm reading it right.
As I've plenty of room to relocate the heater, I'll site the thing over 3m from the closest tap & save the 50 notes for an expansion tank I think. Cheers.

 

[Agile]

Matt should have explained why!

Hot water can allow legionella bacteria to multiply at about 20-40° C. Thats not deemed a problem if the cold tap is more than 2.8m away.

It does not ACTUALLY have to be 2.8 m away as you could just use a concertina of pipe totally 2.8m amd spaced so it does not heat itself from itself!

Tony

 

[matt1e]

Matt should have explained why!

Hot water can allow legionella bacteria to multiply at about 20-40° C. Thats not deemed a problem if the cold tap is more than 2.8m away.

It does not ACTUALLY have to be 2.8 m away as you could just use a concertina of pipe totally 2.8m amd spaced so it does not heat itself from itself!

Tony

Ok, I will, and it isn't anything to do with legionella

It's all to do with expansion of the water in the heater, if your nearest cold tap is less than 2.8m away, then there is a chance that the hot water in the heater could produce warm water appearing at said tap due to it expanding back towards it.
Don't worry about legionella, it's highly unlikely to be a problem for you as your heater only holds 10 litres anyway but most of all its mains fed unvented.

Matt

 

[ianmcd]

Matt should have explained why!

Hot water can allow legionella bacteria to multiply at about 20-40° C. Thats not deemed a problem if the cold tap is more than 2.8m away.

It does not ACTUALLY have to be 2.8 m away as you could just use a concertina of pipe totally 2.8m amd spaced so it does not heat itself from itself!

Tony

Ok, I will, and it isn't anything to do with legionella

It's all to do with expansion of the water in the heater, if your nearest cold tap is less than 2.8m away, then there is a chance that the hot water in the heater could produce warm water appearing at said tap due to it expanding back towards it.
Don't worry about legionella, it's highly unlikely to be a problem for you as your heater only holds 10 litres anyway but most of all its mains fed unvented.

Matt

agreed its nothing to do with legionella the unit uses the length of pipework to absorb any expansion that takes place hence if the length is too short you need to add some other way to absorb the expansion when heated

 

[Agile]

I dont think copper pipe is going to absorb any expansion!

I am sure its becaue they dont want any warm water with legionella being drunk from the cold tap!

 

[gasbanni]

I dont think copper pipe is going to absorb any expansion!

I am sure its becaue they dont want any warm water with legionella being drunk from the cold tap!

Come on agile be told..........its not legionella its to do with the safe operation of the appliance.

Get your forceps, stethoscope, ocillascope and flux capacitor and check it out !

and don't use candles to look for draughts !

 

[gasbanni]

I dont think copper pipe is going to absorb any expansion!

I am sure its becaue they dont want any warm water with legionella being drunk from the cold tap!

Why do you think warm water is going to come out of the cold tap ?

 

[ianmcd]

I dont think copper pipe is going to absorb any expansion!

I am sure its becaue they dont want any warm water with legionella being drunk from the cold tap!

Well its good that you are sure, but you are still wrong

 

[Nige F]

It does not ACTUALLY have to be 2.8 m away as you could just use a concertina of pipe totally 2.8m amd spaced so it does not heat itself from itself!

Tony

Anyone done this - apart from Agile and me

 

[Norcon]

It does not ACTUALLY have to be 2.8 m away as you could just use a concertina of pipe totally 2.8m amd spaced so it does not heat itself from itself!

Tony

Anyone done this - apart from Agile and me

Thats a get out providing the mains still allows upstream expansion and the mains pressure is below that specified by the manufacturer.

FAO OP
Hyco wrote
THE SUPPLIED 6 BAR PRESSURE RELIEF VALVE MUST ALWAYS BE FITTED.
THERE MUST BE NO OBSTRUCTIONS IN THE PIPEWORK BETWEEN THE HEATER AND THE RELIEF VALVE.
THE RELIEF VALVE MUST DISCHARGE TO A SAFE AND VISIBLE PLACE.

 

[steve32]

You need to be G3 (un-vented) registered to install these heaters ALL unvented heaters now come under G3 Regs.

They are not a diy install

 

[matt1e]

You need to be G3 (un-vented) registered to install these heaters ALL unvented heaters now come under G3 Regs.

They are not a diy install

Source please
As far as I'm aware 15 litres or under is ok

Matt

 

[Agile]

I dont think copper pipe is going to absorb any expansion!

I am sure its becaue they dont want any warm water with legionella being drunk from the cold tap!

Well its good that you are sure, but you are still wrong

OK, well if you disagree then please provide a properly reasoned technical argument why 2.8 m of copper tube is going to make any difference at all to the ability to deal with the expansion of 10 litres of hot water!



To Gasbanni, the hope is that the 10 litres of water will expand back up the supply pipe. The extent of that expansion will be well contained within the volume of the 2.8 m of tube so that the cold water at the tap cannot become heated ( and a legionella risk ! ).

Tony