Central Heating revision notes
System design, heat loss and gain, sizing of boiler, emitters, pipework, pump and vessel, commissioning and fault diagnosis.
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System Selection & Design
Low-Temperature and Heat-Pump-Ready Design
Designing wet systems for low flow temperatures so they run efficiently now and suit a future heat pump.
Sealed and Open-Vented Systems Compared
The components, pressures and trade-offs that separate sealed from open-vented heating at Level 3.
System Selection and Fully-Pumped Design
How Level 3 system choices — fully pumped, zoned, interlocked — shape an efficient modern wet central heating layout.
Heat Loss & Gain
Design Temperatures and Degree of Exposure
Choosing internal and external design temperatures and allowing for the building exposure when assessing heat loss.
Fabric Heat Loss and U-values
Calculating heat lost through the building fabric using U-values and the Q = U x A x deltaT method.
Ventilation Heat Loss and Air Changes
Working out the heat needed to warm incoming fresh air using the 0.33 x N x V x deltaT method.
Sizing: Boiler, Emitter, Pipe, Pump & Vessel
Expansion Vessel Sizing for Sealed Systems
Sizing a sealed-system expansion vessel from the system volume, the expansion factor and the acceptance factor.
From Total Heat Loss to Heat Source Size
Turning summed room heat losses into a sensibly sized boiler or heat pump without gross oversizing.
Pipe Sizing and Circulating Pump Selection
Finding flow rates from the heat carried, sizing pipework, and selecting a pump from the index circuit resistance.
Radiator Sizing and Correction Factors
Selecting radiators from catalogue outputs and correcting them for systems that run cooler than the test condition.
Regulations & Information Sources
Filling, Flushing & Commissioning
Handover, Records & Maintenance
Controls Wiring, Testing & Fault-Finding
Carry the design assumptions through every heating calculation
For Level 3 plumbing revision, connect room heat loss to emitter selection, operating temperatures and the complete heating system. Show where each input came from. A correct calculation using the wrong design conditions still leads to the wrong selection.
Use the radiator sizing calculator to explore output at different temperature differences and the expansion-vessel calculator for its separate sizing exercise. Revisit heating-system fundamentals when a design problem reveals a gap in layouts or controls.
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