Combi boiler and hot water

[GreenArmy]

Just want some opinions from experienced and technically minded plumbers/boiler engineers.
Has anyone got a theory on hot water supply pipe sizing from a combi boiler? Most combis these days have 15mm coming from boiler and all bath taps are 22mm as well as old cylinder/tank fed hot water supplies to bath are/were 22mm. So do you think its time bath taps are supplied with 15mm threads for combi boilers as well as 22mm for other systems and should old 22mm pipe be replaced with 15mm pipe when upgrading an old system with a new combi? Or do you think i talking poo and it will make no difference?

 

[radswilldo]

I always decrease down to 15mm as far as possible when doing conversions, the 22mm becomes a restriction to flow rate otherwise,( have done this for customers when involved with other work, the difference is very noticable. The main point with taps is that if they are low pressure the customer should be advised(at their pleasure) to upgrade them. As long as the end result is the manufacturer's flow rate, then you have done your job proffessionally.

 

[newbie1]

flow rate is determined by the boiler as it will only flow what it is designed to flow the difference is the pressure drops slightly when you flow 15mm into 22mm
not likely anyone will swallow the extra cost of removing old 22mm to run new 15mm especially as it normally runs under floor under bath etc
a good engineer should be looking at the intended use for boiler
combis are for flats 1-2 bed single or 2 person etc unless you get the larger ones
a familly needs a system or regular boiler imho

 

[radswilldo]

A combi is fine up 3-bed 1 bath low occupancy homes. When doing boiler replacements I always take customers through all options and if a three bed house, ask will they be adding an en-suite. Restriction is restriction, I have a number of times corrected pipe work/removed needless valves so that a customer can recieve there correct flow rate( this is when the custome has the required pressure and flow rate entering the boiler.