How much chemical cleaner do I need for a power flush?

The standard dosing rate is 1 litre of cleaning chemical per 10 litres of system volume. A typical 10-radiator system holds about 100 litres, requiring 10 litres of cleaner. Some manufacturers recommend higher concentrations for heavily contaminated systems.

How long does a power flush take?

Allow approximately 30 minutes per radiator for thorough flushing. A 10-radiator system typically takes 5-6 hours. Heavily contaminated systems may take longer. The flush is complete when dump water runs clear from each radiator.

Is a power flush necessary when fitting a new boiler?

Most boiler manufacturers require the existing system to be cleaned and flushed before connecting a new boiler. This is typically a condition of the boiler warranty. BS 7593:2019 also requires system cleanliness for new boiler installations. At minimum, a thorough flush and inhibitor treatment is required.

How much water does a power flush use?

A power flush machine circulates at about 80-150 litres per minute internally but uses mains water for dumping dirty water. Total mains water usage is typically 500-2000 litres depending on system size and contamination level. Each dump cycle uses roughly the system volume.

What inhibitor should I add after a power flush?

After flushing, add a quality corrosion inhibitor at the correct dosing rate (typically 1 litre per 100 litres of system volume). Popular UK brands include Sentinel X100 and Fernox F1 Protector. Record the inhibitor type and concentration on the benchmark certificate.

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Power Flush Calculator — Chemical Dose & Duration

Calculate chemical dose, flush duration, water usage and inhibitor re-dose for power flushing heating systems. Based on system volume and condition.

System Size

Approximate system size

Number of Radiators

Total radiators to flush

System Age

Age of heating system

How We Calculate This

This calculator estimates the chemical requirements, duration, and water usage for power flushing a central heating system. It helps plan the job and quote accurately for materials.

Calculation method

System volume: Estimated from radiator count (~10L per radiator + boiler + pipework)
Chemical dose: System volume ÷ 10 = litres of cleaner
Duration: Number of radiators × 30 minutes
Water usage: Flow rate × dump cycles × system volume
Inhibitor: System volume ÷ 100 = litres of inhibitor

Always follow BS 7593:2019 guidelines for system cleaning. Record all chemicals used and their concentrations on the system benchmark or handover documentation.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.