How to size a boiler

[New_gas]

Just doing my ACS and I was hoping the course taught you how to correctly size a boiler. Turns out it doesn’t, just wondering how you guys size a boiler whether it’s be system, heat only or combi

 

[ShaunCorbs]

Heat only / system actual load of the system or you can stagger hot water then just size to rads / load

combi hot water flow rate (eg size to mains cold water flow)

 

[Knappers]

For Regular/system
Usually 1-2Kw per rad and about 3-4Kw for hot water (unless w-plan)
There's plenty of rad calcs out there and if you've got a big cylinder it would be best to adjust for it.
A modern cylinder will make use of much more than 4Kw but if you greatly oversize the boiler (as many do) you'll end up having a less efficient heating system (and who heats their water from cold)

 

[Brambles]

If you want to move onwards and upwards you need to be able to correctly size each room on a heat loss /hr basis.
If you don’t and use ad hoc rules of thumb in the air, you will probably survive in gas / oil - but not in renewables

 

[Knappers]

If you want to move onwards and upwards you need to be able to correctly size each room on a heat loss /hr basis.
If you don’t and use ad hoc rules of thumb in the air, you will probably survive in gas / oil - but not in renewables

I feel there is a dig there somewhere?
It is quite a rich topic and it does depend what your doing.
Personally If i were you I'd use an app to calculate my heat requirements for each room. Size rads or UFH and boiler to suit.
For the vast majority of domestic work 22mm mains with 15mm branches will be what you want but I would recommend learning appropriate loads and lengths for 10mm (especially plastic)
If you do some research into flow rates and pressure drops in pipework then you should quickly develop a sense of suitable pipe sizes and lengths of runs, to ensure your getting good flow to rads while not exceeding pump head.
Your course should teach you best practice when it comes to pipe runs and system layout.

After a while you'll get familiar with it and a thumb in the air will likely get you within a pipe size and 6kw, just be more cautious on bigger installs and go back to basics

 

[Knappers]

Thats still a fairly basic way to keep yourself out of trouble. For any large or unusual project id reccomend getting someone else to do the spec.