Boiler 15mm gas connection pressure loss why not 22m connection?

[cascas]

On a boiler over 30kw that has a 15mm gas connection, how can you calculate pressure loss of the final 15mm pipework.

usually the final 1m is reduced to 15mm, however 15mm pipework is only rated at 2.9m3/hr over 3m, with no data for shorter runs in most of the tables.

A 30kw boiler will have a gas rate over 3m3/hr, even at 2.9m3/hr (i.e 28kw boiler) 0.5m final pipe to the boiler with elbow to connection will cause a 0.33mbar pressure drop which seems excessive for such a short run.

Why are boilers not fitted with 22mm connections.

 

[Mike Jackson]

So if you've got 1/3 mbar drop over that metre just size the rest of the pipework accordingly. Alternatively come out of the 1/2" connection and step straight up to 22.

 

[kirkgas]

thats the way ive always done it, 22mm elbow with 22 x 15 reducer in it right under the boiler with 100mm of 15mm pipe into the boiler, saves any hassle