Turndown Ratio

Turndown ratio is the ratio of a burner's, boiler's or valve's maximum rated output to its minimum stable output. A higher turndown means the equipment can modulate over a wider range without cycling off.

A boiler with a 10:1 turndown can fire stably anywhere from full load down to one-tenth of capacity. High turndown matters because it lets equipment follow a falling demand by modulating rather than switching off and reigniting. Cycling wastes energy through purge losses and standby heat loss, and it stresses components. Burners, control valves and pumps are all specified partly by turndown to ensure stable, efficient operation across the real load profile.

Related terms

Boiler Efficiency · Excess Air · VFD (Variable Frequency Drive)