Advice needed - 10mm system conversion?

[ShaunCorbs]

cheers Shaun, I'll give that a go first... the white is very crusty and the greeny/blue corrosion is very oily/sticky so assumed I'd have to use white spirit and wire wool etc...

I can't work out why there's splashes of this green stuff on top of the pipes though - baffled

its flux from where they dont wipe the joints you might need warm water yo take that off

 

[doitmyself]

Looking into systems i think that an unvented system will be the way forward in the future - the mains appears strong (not measured yet but pretty certain it'll be good for the unvented), a combi just causes too much issue especially when I'm cleaning the car and she's showering! We also have a very low pressure mains fed stat shower in the en suite which is virtually unusable due to rubbish pressure

Those two statements are contradictory.

As for a combi being no good while, by implication, an unvented cylinder will be OK, that, to put it mildly, is not true. Both are mains fed, so you will have exactly the same problem cleaning the car while she is showering whichever method you use.

You need to check the incoming flow rate and pressure before making a decision. It's easy to do.

If you have a garden tap (normally fed from the mains - check first), measure the flow rate using a marked bucket and watch.

Now repeat (at garden tap) with the kitchen cold tap turned on fully at the same time.

If there is no mains fed garden tap, just do it at the kitchen tap; but be aware that some taps restrict the water flow, which is why the garden tap is preferred.

You need a minimum flow of 20 litres/min for an unvented or a combi.

How well is the house insulated? Double glazing? Cavity walls? Loft? You can get grants for walls and lofts - check out your gas/ electricity supplier.

 

[Jimbobber]

No sorry but you can't compare a combination boiler with a pressurised cylinder. You are right that you need ample pressure to make unvented systems give good performance. At least 3 bar is OK.

A combination boiler provides instantaneous hot water and in no way can be compared to the performance of an unvented cylinder. Completely different systems.

 

[doitmyself]

No sorry but you can't compare a combination boiler with a pressurised cylinder. You are right that you need ample pressure to make unvented systems give good performance. At least 3 bar is OK.

A combination boiler provides instantaneous hot water and in no way can be compared to the performance of an unvented cylinder. Completely different systems.

Both systems rely on the mains pressure to push the water out of the tap. The only difference is that the unvented cylinder acts as source of hot water in the path between the mains input and the tap, so the water does not have to be heated instantaneously.

If you have five litres/min from the mains, you will get five litres/min coming out of the tap irrespective of which system you have.

Pressure and flow rate are not the same thing.

 

[ShaunCorbs]

Both systems rely on the mains pressure to push the water out of the tap. The only difference is that the unvented cylinder acts as source of hot water in the path between the mains input and the tap, so the water does not have to be heated instantaneously.

If you have five litres/min from the mains, you will get five litres/min coming out of the tap irrespective of which system you have.

Pressure and flow rate are not the same thing.

but the question is why will an unvented do more than one bathroom decent and a combi will not (note this is not a question)

 

[doitmyself]

you can upgrade to 15mm and it will give increased flow to the rads.

You don't need increased flow; you need the correct flow, which is determined by the rad output and the required temperature drop.

Yours being open vented at the moment would be better with 15mm as this would help prevent the black sludge from blocking the pipes.

But a 15mm pipe will have a lower water velocity (metres/sec) than a 10mm (for the same flow rate), so there is more likelihood that sludge will block the pipes, particularly of there are long horizontal runs. A 10mm pipe can carry 2.5kW at an 11C drop and 4.5kW with a 20C drop.

 

[Jimbobber]

Combination boilers serve a purpose a bit like an electric shower (when needs must), good for a flat or a small 2 bed house maybe.

But the carcass will be in 15mm pipe for a start. Unvented cylinder will be at least 22mm distribution and larger for a big property.

Also a combination boiler doesn't give you full mains flow rate, there is a reduction as to be expected. Running a shower off of a combi ? Um yeah lovely system:uhoh2:

We fit combi's in a lot in new builds sometimes in quite large property's running one shower and the rest electric, but remember just because big building companies are specifying this doesn't make it good practice, it's just profitable haha

 

[1animal1]

I'm by no means an expert as you've probably guessed. But I have done a lot of reading on this and apparently the unvented gives you the same hot water pressure no matter how many taps are running, combis simply cannot do this, I've experienced a large combi and as good as it was.... It could not handle more than two hot taps at once without a significant pressure drop.

Diy, are you saying I'm likely to get the same drop with an unvented?

 

[Jimbobber]

1animal1 you're barking up the wrong tree listening to Mr Diy, he clearly doesn't do this for a living. An unvented cylinder will easily outperform a combi.

What system you size and spec will depend on your intended usage and size of your house etc. Eg if you had a very big house, you could have say a 350ltr cylinder and distribute in 28mm pipe. For your more average 3 or 4 bed house distribute in 22mm pipe with a 200-250ltr cylinder. If you've got good mains pressure it's all good unk:

 

[Ermintrude]

AFaiy