oil boiler size quandary

[TFGplumbing]

Hiya guys

I'am in a bit of a stick

Small bungalow with a heating requirement of about 12.5 KW that includes an additional 10% heat loss on pipework.

One bathroom & one kitchen, customer has a bee in their bonnet about HW performance

Dynamic CW pressure of 1.2
CW flow rate of 18 litres per min

I know a heatslave 12/18 is going to do the job CH wise; It requires 1.5bar dynamic cw to provide 15/trs per min on the HW

But part of me wants to spec a 18/25 & put it on a low range 18KW nozzle just because it provides more HW flow rate & requires slightly less dynamic CW pressure to attain 18ltr per min on HW.

But if I choose the larger boiler its going to be approx 5.5KW bigger than needed & Iam just wondering if thats going to stop the boiler condensing as well as it should as oil boilers don't modulate.

Thanks for reading anyway

 

[lame plumber]

If they want massive HW rates etc go for an unvented cyl, or they have to accept that combis arent all they are cut out to be

 

[TFGplumbing]

If they want massive HW rates etc go for an unvented cyl, or they have to accept that combis arent all they are cut out to be

Thanks for the reply, they dont want a cylinder

 

[SimonG]

Do what you need to do to make them happy. Sometimes the cust cant see the wood for the trees and cant be educated.