How to Size a Dirt & Air Separator for Central Heating Systems

Why Correct Sizing Matters

Correctly sizing a dirt and air separator is critical to ensuring effective removal of contaminants and air from a central heating system. An undersized separator may fail to capture debris or microbubbles, while an oversized unit can lead to unnecessary cost and installation challenges.

Proper sizing improves:

  • Separation efficiency
  • System reliability
  • Energy performance
  • Component lifespan

 

Key Factors to Consider When Sizing a Dirt & Air Separator

1. System Flow Rate (Primary Factor)

The most important sizing parameter is system flow rate, typically measured in litres per hour (l/h) or cubic metres per hour (m³/h).

  • Flow rate determines how long contaminants remain inside the separator
  • Higher flow rates require larger internal separation chambers

Best practice:
Always size the separator to handle the maximum system flow, not the average operating flow.

 

2. Pipe Diameter

Dirt and air separators are sized to match pipework diameters to maintain optimal flow velocity.

  • Incorrect pipe sizing can reduce separation efficiency
  • Most Altecnic separators are designed for standard pipe sizes

Avoid using reducers unless specified in the manufacturer’s guidance.

3. System Type

Different systems generate different contamination risks:

  • Boiler systems: High magnetite formation
  • Heat pumps: Low tolerance to contamination
  • Underfloor heating: Fine debris and air pockets

Systems with low-temperature operation benefit particularly from high-efficiency air separation.

 

4. Domestic vs Commercial Systems

 

System Type Sizing Priority
Domestic Compact size, magnetic filtration
Commercial Flow capacity, separation efficiency
Large plant Flanged separators, low pressure loss

 

Where to Install for Best Performance

For optimal sizing performance:

  • Install on the flow pipe
  • Place close to the heat source
  • Position where temperature is highest and pressure is lowest

This maximises both dirt settlement and air release.

Common Sizing Mistakes to Avoid

  • Sizing based only on pipe diameter
  • Ignoring peak flow conditions
  • Using undersized separators for heat pumps
  • Omitting magnetic filtration in sealed systems

 

Altecnic Support

Altecnic provides:

 

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