Boiler replacement in renovation

ModernSlave

We currently have a gravity fed system and are looking to install (and move to the utility room) a combi boiler to replace the old vented boiler that uses a chimney. So far two plumbers have come around to quote.
Plumber A has recommended running 22mm pipes back to the original boiler cupboard to connect to the original pipe work.
Plumber B has said that connecting back to the original cupboard isn't necessary as the pipework will be pressurised. Once moved to the utility room he recommends connecting to the nearest radiator using the 15mm pipes currently in place and the hot/cold from the utility room washing machine pipes.
Does it matter if you connect to 15mm rather than 22mm when installing a combi like this? House is a small 4 bed.

Thanks in advance

magn8p

We have a Worcester Combi and the pipes are 15mm. This is a 3 bed semi built in 1960s and I guess originally the house never had a central heating system but has since been updated twice. The new boiler installation was done last year and the pipes are definitely not new so are the radiators - atleast 15 years old or over.

So, in essence, I think you are absolutely fine wiht 15mm pipe work.

However if you are talking about the gas supply pipe, it defintely needs to be 22mm. For more info please check https://www.superwarm.co.uk/combi-boilers-why-you-may-need-to-upgrade-your-gas-pipes/

All the best.

ModernSlave wrote: »

We currently have a gravity fed system and are looking to install (and move to the utility room) a combi boiler to replace the old vented boiler that uses a chimney. So far two plumbers have come around to quote.
Plumber A has recommended running 22mm pipes back to the original boiler cupboard to connect to the original pipe work.
Plumber B has said that connecting back to the original cupboard isn't necessary as the pipework will be pressurised. Once moved to the utility room he recommends connecting to the nearest radiator using the 15mm pipes currently in place and the hot/cold from the utility room washing machine pipes.
Does it matter if you connect to 15mm rather than 22mm when installing a combi like this? House is a small 4 bed.

Thanks in advance

southcoastrgi

It depends on rad sizes, but as a very rough rule of thumb 15mm will feed 3 rads or 15,000 btu,s, so no I wouldn’t connect onto 15mm to feed your heating

Alex1983

I agree, I wouldn’t do it. It might work but you must have at least 10 rads you may get circulation issues straight away or at a later date.

ModernSlave

Thanks for feedback

beaker141

southcoastrgi wrote: »

It depends on rad sizes, but as a very rough rule of thumb 15mm will feed 3 rads or 15,000 btu,s, so no I wouldn’t connect onto 15mm to feed your heating

Just watch plumber B doesnt then agree to use 22mm pipe to the nearest rad and then tee it into the 15mm pipe !!! :rotfl:

I've always run 22mm flow and return along the landing/hallway and tapped off to each rad from that using 15mm.

I assume from the above, I could reduce this down to 15mm at the point on the run where I know its feeding 3 or less radiators rather than as I have now, at the end of the 22mm straight run then reducing to 15mm for just the last radiator.

martinsurrey

ModernSlave wrote: »

Thanks for feedback

Even a small 4 bed will have at least 8 rads (4 beds, bath, living, kitchen, hall) more likely 10, 8 rads through a single 15mm pipe is lunacy.

I would be going with A