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Central Heating

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

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Heat Emitters

Heat Loss Calculation

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Where Should You Install a New Radiator?



Heating system water analysis



Circulating Pump

Heating System Controls

Minimum Requirements

Room Thermostats



Heat Emitters

Heat Loss Calculation

Radiator Sizing



Fully Pumped Hot Water and Central Heating

Gravity Hot Water and Pumped Central Heating

Gravity System

Open-vented System

Pipework Sizing

Pipework Systems

Sealed Systems

System Layout

Underfloor Heating


Boiler Sizing

Flue Types

Gas Boilers

Heat Pumps

Oil Fired Boilers


Solid Fuel Boilers

Heat Loss through Ventilation

  • Air Change (W) = 0.33 x Cubic content of the room (m3) x  Temperature rise (ºC) x Number of air changes (1/h)
Heat Loss through Building Fabric
  • Building Fabric (W) = Area (m2) x U-value (W/m2) x Temperature rise (ºC)
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Room Temperature and Ventilation Rates

(BS5449-Section 3 1990)

Room Temperature °C Air changes (1/h)   Area U-value W/m2
Living 21 1.5 Floor 0.36
Dining 21 1.5 External wall 1.0
Bed/sitting 21 1.5 Internal wall 1.9
Bedroom 18 1.0 Window 2.9
Hall/landing 18 1.5 Roof 0.34
Bathroom 22 3.0    
Toilet 18 3.0    
Kitchen 18 2.0    
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U-values of Building Fabric

Construction W/m2/°C Construction W/m2/°C
External solid wall 2.0 Ground floor - solid 0.45
External cavity wall 1.0 Ground floor - wood 0.62
External cavity wall (filled) 0.5 Intermediate floor - heat flow up 1.7
External timber wall 0.6 Intermediate floor - heat flow down 1.5
Internal wall 2.2 Flat roof 1.5
Window - single glazed 5.7 Pitched roof (100mm insulation) 0.34
Window - double glazed 3.0 Pitched roof (no insulation) 2.2
Internal wall - solid block 2.1    
  • All calculations are made for -1°C outside temperature
  • Intermittent firing = 15%
  • Number of air changes required in rooms with solid-fuel open fires increase greatly
  • 10°C - temperature difference for semi-detached houses
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