Boiler advice

grumbler

They are small and, AFAIK, intended only to accommodate the water expansion  with increasing temperature and only in the CH loop. Basically, that's what small expansion tanks in the loft do in vented systems.

Jeepers_Creepers

That could well be the case, Grumbler.

EDIT: A wee bit of research suggests that there is also a small EV for the main cylinder, but only to accommodate the expansion of the stored water as it's heated - which makes sense since, with no tap open, it would be a sealed system undergoing an increase in pressure due to the stored water being heated up, which would be a bit scary.

I'd got it in to my head that this vessel was to keep the tank's delivery pressure nice and constant if more than one tap was opened.

And then there's a separate EV for the actual boiler system.

southcoastrgi

tacpot12 said:

 You can always add pumps to the showers if the flow rates from the cylinder are not adequate, 

No you can't add pumps

southcoastrgi

Jeepers_Creepers said:

I'd got it in to my head that this vessel was to keep the tank's delivery pressure nice and constant if more than one tap was opened. 

That's an accumulator not a expansion vessel  

330d

Thank you all for the replies, some very good info here.

I think I am leaning towards keeping the system boiler setup. Yes it maybe not as efficient as a combi but then again I am not degrading the hot water performance. What I might do is move the boiler and water cylinder into the loft.

Out of interest, what size hot water cylinder is the minimum you would recommend? 5 bedroom house and 4 occupants.

I am assuming if the cylinder is too large it will be inefficient as I will be heating water that wont be used?

southcoastrgi

50 ltrs/person plus 50 ltrs so either 250 or 300, just bare in mind your loft will probably have ceiling joists that aren't designed to take any real weight, 1 litre of water is 1 kg plus the empty weight of the cylinder so you will have to take that into account, plus the higher you put the cylinder the less the pressure you will get 

grumbler

southcoastrgi said:

 plus the higher you put the cylinder the less the pressure you will get 

Why is that?

330d

southcoastrgi said:

50 ltrs/person plus 50 ltrs so either 250 or 300, just bare in mind your loft will probably have ceiling joists that aren't designed to take any real weight, 1 litre of water is 1 kg plus the empty weight of the cylinder so you will have to take that into account, plus the higher you put the cylinder the less the pressure you will get 

Thank you. I am aware of the weight but think I should be fine as there is a unused water tank in the loft. Don't know the capacity of it but was going to measure it and work out the capacity. I suspect it will be a few hundred litres as it does look big. 

If the loft is strong enough for the tank then it should be ok for the cylinder. But I will get my builder to confirm.

southcoastrgi

grumbler said:

southcoastrgi said:

 plus the higher you put the cylinder the less the pressure you will get 

Why is that?

Pressure will reduce as you go up, 2 bar on the ground floor won't be 2 bar in the loft 

grumbler

southcoastrgi said:

grumbler said:

southcoastrgi said:

 plus the higher you put the cylinder the less the pressure you will get 

Why is that?

Pressure will reduce as you go up, 2 bar on the ground floor won't be 2 bar in the loft 

Yes, but what was lost will be added back when the pipe goes down to the taps, shower etc. It will be the same 2 bar in the ground floor kitchen.