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Unvented Hot Water Storage System

Exam revision materials for Plumbing Level 2&3 and ACS Gas Safety test

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Unvented Cylinders

Lagging and Insulation

Pipework insulation

  • Regulations
    • TIMSA "HVAC guidance for achieving compliance with part L of the Building Regs

  • In order to prevent a heat loss through the pipe maximum length of Uninsulated hot water pipes from the cylinder should be:
    • Pipe diameter 12mm – 20m uninsulatied pipework
    • Pipe diameter 12-22mm – 12m uninsulatied pipework
    • Pipe diameter 22-28mm – 8m uninsulatied pipework
    • Pipe diameter over 28 – 3m uninsulatied pipework
  • To support an insulated pipes two piece spacing clip are used

Hot water pipes heat loss*

Pipe outside diameter mm 8 10 12 15 22 28 35 42 54
Maximum heat loss W/m 7.06 7.23 1.35 7.89 9.12 10.07 11.08 12.19 14.12

*Based on: horizontal pipe at 60°C in still air 15°C

< Go Back2014-04-12

Cylinder insulation

  • Unvented cylinder standing heat loss in 24 hours < 1.6x(1.28 for high performance)x(0.2+0.051V)kWh
    • Cylinder: 120L; 15L/min - 20min to reheat
  • MAX cylinder heat loss – 1W/L
  • Vessel Insulation
    • 35mm thick of PU-foam
    • MIN density – 30kg/m2
  • 15mm thickness for Thermal Conductivity (K) – 0.045 W/mK
< Go Back2014-04-12