Worcester 42CDi Gas Rate

[CES]

This is doing my head in, Im trying to calculate a new gas pipe run as the numpty who installed it used 22mm pipe on about a 25m run. So I've got the MI's out to check the gas rate, heat input etc and they say 4.4m[SUP]3[/SUP]/hr and max kw of 42.
Now this doesn't add up in my head as 4.4m[SUP]3[/SUP]/hr works out as 47kw and working back 42kw should give a gas rate of about 3.9m[SUP]3[/SUP]/hr.
Am I getting the early onset of dementia? or are the MI's wrong?

 

[aggis]

You don't suppose the boiler is a 42 kw output with a 47 kw input, 4.4m3/hr

 

[johnnyplumb]

your right worcester goes quote 42 kw & 4.4 m3/hr gas rate for a 42 cdi,
but the 42kw is heat input [net], you need to change net to gross, ie 42 x 1.11 = 46.62

4.4 x 38.6
3.6 = 47 kw boiler efficiency = 42 divided by 46.62 = 90%


as for pipe size, you can run 28mm around 30m [for 4.4m3/hr ], so for a 25m run and allowing for a few bends and no other appliances, you might just get away with 28mm pipe, realistically your gonna need some 35mm pipe if there's other appliances.

 

[CES]

Cheers, it says max rated heat input as 42 and max rated heat output as 42, I should have clicked. It would help if they were a bit clearer with their MI's though I thought I was losing it.