DIY Doctor UK DIY Forums

Hi
I'm just installing a electromax electric flow boiler and dwh unit and want to know what size copper pipe to use for the heating system the the outlets from the unit are 22mm can i downsize to 15mm immediately as i don't fancy notching 22mm pipes in every where the unit is housed upstairs and there are a 3 radiators upstairs and three downstairs the unit is 9kw output and the radiators are a total of 6kw. Also i'm replacing my immersion heater with this unit and currently the cold water mains supply to the immersion cupboard is only 15mm is this going to be a problem.

15mm mains cold water is normal, this will not be a problem.

Boiler flow and return pipes are best ran in 22mm pipe from the boiler to the manifolds, or 22mm pipe with 15mm legs going to the radiators.

Piping the heating sytem straight from the boiler in 15mm pipe will work, but you will find the radiators will not heat up as much as it would with 22mm, plus the last radiator in the system will struggle to give off much heat.

I know someone having problems with their heating as it takes about 25mins for radiators to even get warm downstairs, their's is all in 15mm copper pipe.

Can i run 22mm under the floor boards up stairs and then branch off into 15mm for the last couple of meters to the downstairs radiators so the pipes running down the walls are only 15mm and not so horrible to look at.

yes, normally only 15mm to radiators tee'd into 22mm flow and return