Sizing replacement boilers

[jim221189]

What is a general rule of thumb of sizing boiler that everyone applies when commencing a quote??

 

[SimonJohns]

Nowadays with combis the heating requirement is insignificant compared to the hot water requirement

I tend to spec the largest possible combi practicable but if they want a system boiler then out comes the mears gauge

Radiators have come a long way since back in the day.

 

[bright spark]

If its for a replacement boiler. Have a quick look at the building, ask the customer about how quickly the old boiler hit temp, check the size of the existing gas supply pipe to suit new boiler, for the running pressure. Manufacturers supplying to Ireland specify between 15 and 20 mbar. You don't want to be caught out putting in a new boiler using the existing gas supply with not enough gas.
If its for a new build, the architect should have the information. Bounce it back off him and let him specify the boiler size.

 

[Mike Jackson]

If it's not a combi I do a whole house calculation to work out the heat requirements. There's a lot of over sized boilers out there and putting the same size back in won't maximise the savings.

 

[hammers4spanner]

If its for a replacement boiler. Have a quick look at the building, ask the customer about how quickly the old boiler hit temp, check the size of the existing gas supply pipe to suit new boiler, for the running pressure. Manufacturers supplying to Ireland specify between 15 and 20 mbar. You don't want to be caught out putting in a new boiler using the existing gas supply with not enough gas.
If its for a new build, the architect should have the information. Bounce it back off him and let him specify the boiler size.

Loads of new builds have incorrect boiler sizing .

I wouldnt fit anything less than 28 kw regarding a combi
system/heat only generally 3 kw to cylinder then rad calc to be honest you can do it over phone regarding boiler size dont even get off sofa to price them .
The biggest concern is will it fit back in situ o.k imho

 

[AWheating]

new builds are normally specified by either the heating company doing the work or the boiler/radiator manufacture. It is sometimes done by a specialist design engineer on behalf of the architect/builder but only normally on large one off houses.

The heat loss u values would be available from the architect