BES supply vented and unvented cylinders. Our vented copper cylinders are grade 3 with a maximum working head of 10m, 25mm standard insulation and large heating coil. They comply with Part L Building Regulations. The unvented stainless steel cylinders are able to withstand mains pressure. Unvented hot water cylinders are WRAS, WRc-NSF and BEAB approved with each cylinder being pressure tested to 15 bar.