How much cleaner do I need for my heating system?

Standard system cleaners are typically dosed at 1 litre per 10 litres of system volume. For a typical 100-litre system, you need 10 litres of cleaner. Descalers may use a stronger ratio (1:8), while biocides are more dilute (1:20). Always follow the specific manufacturer’s dosing instructions.

How long should system cleaner circulate?

Standard system cleaners need a minimum of 1 hour circulation at full temperature (or as specified by the manufacturer). Some cleaners can be left in for up to a week for heavily contaminated systems. Descalers typically need 4-8 hours. Never leave cleaner in longer than recommended.

Why is inhibitor important after cleaning?

After cleaning and flushing, the system contains fresh, untreated water which is corrosive to steel and iron components. Corrosion inhibitor forms a protective film on internal surfaces, preventing rust and magnetite formation. BS 7593:2019 requires inhibitor to be added to all new and cleaned systems.

How do I check inhibitor concentration?

Most major inhibitor brands (Sentinel, Fernox) include a molybdate tracer that can be tested with a simple dipstick or test kit. The concentration should be above 50 ppm molybdate. Test annually at each boiler service and top up if low. Record the result in the service documentation.

How much water does a system flush use?

A basic drain-down and refill uses approximately the system volume (80-150 litres). A thorough flush with multiple fill/drain cycles uses 3-5 times the system volume (240-750 litres). A power flush with a dedicated machine uses significantly more — see the power flush calculator.

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Heating Cleaner Calculator — Chemical Dosing

Calculate system cleaner dose, circulation time, flush volume, and inhibitor re-dose for heating system maintenance per BS 7593:2019.

System Volume

Total heating system water volume

Number of Radiators

Total radiators on system

Chemical Type

Type of treatment

Inhibitor Type

Inhibitor concentration

How We Calculate This

This calculator determines the chemical dosing requirements for heating system cleaning and treatment in accordance with BS 7593:2019 and manufacturer guidance.

Dosing method

Cleaner dose: System volume ÷ dosing ratio (typically 1:10)
Circulation: Minimum time at operating temperature
Flush volume: System volume × number of flushes
Inhibitor dose: System volume ÷ 100 (standard) or ÷ 200 (concentrated)

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.