I had a problem with my Gas boiler and called an engineer out from a local Crondall, Surrey UK company. The engineer felt my installation was commercial even though past engineers over 13 years have never said anything like this. My installation is different as I have 2 x worcester bosch 30cdi (30kw each) and my understanding is that it needs to be over 70kw to be commercial. He agreed (after talking to some people on the phone), then he noted I had 35mm copper pipe that ran from the gas meter outside my house to the boilers in my house. The distance was in his opinion between 10 and 12 meters long. I would agreed that is at most 10m but he said 12m. I asked him to explain how he gets it to be "commercial" and he was unable to and said his manager said it was commercial and left! So I did some research and I worked out the following: 1. My boilers are 2 x worcester bosch greenstar 30cdi each is 30kw so total is 60kw and therefore less than 70kw. 2. My pipework is copper 35mm to the boilers and then reduces. So lets say it is 12meters from the meter to the boiler. 3. The gas meter has the follwoing on it: a UGI meters Ltd, A Hanson PLC Company, 1993, 212 f3/hr pmax 50mbar, -071ft3/and R5 (I have attached a pic) So my calcs are as follows (domestic is something where the gas in the pipework and meter is 0.035m3 total. 35mm copper holds 0.00084 per meter The meter holds as follows: E6 = 0.0024 = results in 39m length G4/U6 = 0.008 = results in 32m length G10/U16 = 0.025 = results in 12m length. I am unable to figure out which type my meter is, but I guess it is one of the first 2. I know I have ignored the x0.1 for fittings. But even then I am definately domestic. Are my calcs correct? any comments please?