New combi sizing - overspecced??!

[Phil12345]

Cheers Bob just to give you an idea I just measured flow at my bath tap.

18l/min cold and 8 hot....

I do have braided wafty hoses on my kitchen sink so going to check flow at outside tap too.

 

[bobdogavitch]

I'm sure someone will tell me I'm wrong but if you're getting 18ltr per min at the cold mains fed bath tap it would suggest it's pipework/restrictions that are resulting in your poorer flow rates elsewhere rather than what's actually coming into the house.

 

[Phil12345]

Outside tap just did 2.27 litre milk bottle in 8.2seconds- I make that about 18l/min?

On the same feed as kitchen sink.

That's also where pressure read 3-3.5 bar

 

[bobdogavitch]

Weren't you getting much less before?

 

[Phil12345]

16.6 I beg your pardon

 

[Phil12345]

Yep at kitchen tap about 12-14.

Not measured outside tap flow before, only pressure

 

[bobdogavitch]

Yep at kitchen tap about 12-14.

Not measured outside tap flow before, only pressure

Ok

 

[Dan Robinson]

I see videos (were they yours?) about an unvented if you don't then add an accumulater, the performance is absolutely terrible!

The poor performance was off a tiny pipe with no accumulator.

Kitchen taps are usually very restrictive too.

Unvented cylinders and their associated controls don't restrict flow too much, but most combis do by design.

 

[bobdogavitch]

A stop gap solution would be to install a thermostatic mixer shower, pipe the shower cold feed to the main and fit a single impeller pump on the hot. Yes it would be noisy and you'd empty your cylinder pretty quickly but it would give you much better shower performance. You could also fit a bigger cylinder which would increase shower times. When the time came you could bin the pump and upgrade the cylinder and/or boiler.

 

[Phil12345]

So dan I guess what it boils down to is if you read 16.6l/min and 3 bar pressure at the back tap on a 15mm main, how confident would you be that an unvented in the loft with a brand new 22mm feed from mains would give over 20oddl/min?

 

[bobdogavitch]

I reckon you'd be away with a mixer but I'll bow to Dan's superior knowledge.

 

[Dan Robinson]

I'm out on the tools at the moment, when I get home I'll measure my stuff at home.

 

[Phil12345]

You're a legend dan

 

[Phil12345]

Whereabouts in the world are you dan?

 

[Dan Robinson]

Hertfordshire and North London.