Reverse pipe-sizing

[South-BT]

Hi I'm doing a quote for a customer who currently has a 38kw regular boiler. The size of the house/rads etc. suggests a 24kw or 27kw boiler would be fine. I have done a working pressure test and currently they have a 4.5mb drop over the gas run. I can't see the gas pipe as it runs under the floor, but I see 28mm leaving the meter and 22mm coming up to the boiler. I wanted to know if there was an equation that would allow me to work out the pressure drop of the 24kw & 27kw boilers, going by the 4.5mb drop on a 38kw boiler? Any help is much appreciated. Regards

 

[ShaunCorbs]

Nope sorry you need to know the approximate run