Boiler sizing

[lordyjordy111]

Hi all

was just wondering how everyone sized there boilers....

I normally do combis on hot water flow rate and conventional boilers/hw cylinder on whats already there (if customer is happy with the output of the existing one then why not)

there are a lot of methods but was just wondering what people have used successfully....

also do you use a rule of thumb ie

5 bed 30
4 bed 28
3 bed 24 etc

cheers

 

[Mike Jackson]

Combi hot water requirement

Conventional I do it properly and use the whole house sizing method.

 

[kozak1968]

As Mike says use the whole house boiler sizing method, you can search the web for a calculator.

 

[lordyjordy111]

thanks for your reply

can you expand on the whole house sizing method... links how you do it etc

I bought the cibse design guide but it seems to oversize

 

[Mike Jackson]

Whole house boiler sizing method

 

[tamz]

The whole house sizing method is liable to get you very unhappy customers and lots of complaints on a boiler swap.
You need to go with whatever is fitted by the output of the existing rads.

The whole house method works for new installs but might still leave your customers unhappy. I individually size the rads to the rooms based on heatloss and the boiler to suit not some concocted measure around the house method.

People will never complain they are too warm but they will if they are too cold.

 

[Ollieg]

I always do whole house sizing method on conventional systems and have never had a problem.
If its borderline I consider going up a size ( could they get an extension ).
Got an 837 in my pokey house with a WORKING Pressure of 3.5 bar on the mains. A combi has to be sized on DHW.

 

[tamz]

Btw how can manu's justify the price difference on boilers for basically speeding the fan up?
That one really p issesme off!