Refurbing a property and I need a new gas feed from meter as moving boiler location. Plumber seems to think we need a 25mm pipe but I think he's being over cautious. The boiler will likely be the only gas appliance in the house. The meter is wall mounted outside around 9m away horizontally with a 2m drop to the meter and 2m drop to the boiler say. I imagine it will be around a 30kw boiler. I've got a table up on the internet but its hard for me to interpret with it not being my trade.