Cold supply to unvented cylinder

[Burt Stormberger]

Hi guys,

I've moved into a house which has recently had an unvented cylinder installed.

The house is a mid-80s build. The original setup seems to be that the cold supply to the storage tank in the loft is 15mm. There were then 2 outlets 22mm from the tank - 1 fed all of the cold taps and the other to the vented hot water cylinder in the airing cupboard.

When the unvented cylinder has been fitted, the 15mm cold supply has been used to feed both the 22mm pipe which distributes cold around the house and the cylinder's 22mm input (via a 15-22mm reducer). The cylinder's output is also 22mm.

Everything is working well but there is more of a pressure/flow drop when we have 2 outlets running than we used to get in our previous new build house.

I am wondering if I should replace the 15mm feed pipe between the supply to the house and the unvented cylinder with 22mm or even 28mm.

Would this allow a higher flow rate and thus less noticeable difference when running multiple outlets?

Or am I barking up the wrong tree?

Cheers in advance for help!

 

[ALCPlumbing]

Depends on the size of the incoming main. Do you know what size pipe enters the house? Is it lead? Or plastic? You may need to upgrade all the way to external stopcock to get full benefit of unvented hot water system.

 

[ALCPlumbing]

Upgrading pipework will help.

 

[Burt Stormberger]

Hi ALC,

Thanks for your reply.

Under the kitchen sink there is a plastic pipe on the supply side of the main stop cock - I assume this is the incoming main? This pipe is 22mm as far as I can tell.

It is immediately reduced to 15mm on the 'house' side of the stop cock and this 15mm pipe supplies the kitchen and utility sinks before heading upstairs - presumably to the unvented cylinder.

Interestingly, the hot supply to the kitchen and utility sink is 15mm as well so this must be getting reduced from 22mm sometime after the output from the cylinder.

Which bits would you recommend upgrading? The issue is not a major one as it is possible to have 2 showers at the same time, just at reduced pressure / flow. I don't want to spend too much money but if it's a case of upgrading small amounts of pipe it can be done.

Cheers!
Burt

 

[dcawkwell]

Yes upgrade.

An alternative is to put the non return valve for the unvented cylinder just after the house stop valve. The expansion vessel of the unvented cylinder will therefore balance out any sudden opening and closing of a 2nd outlet.

Also fit aerator taps to sinks as these use less water a 2nd expansion vessel will also help as it will store more cold mains at pressure.

 

[Burt Stormberger]

Cheers dcawkwell

Do you reckon just upgrade the cold supply to the tank or is there anything else I should do while I'm at it?