Boiler Turndown Boiler turndown is the ratio between a boiler’s maximum and minimum output. Depending on the burner’s design, it may have a turndown ratio between 4:1 and 10:1 or even higher. A 4:1 turndown means the boiler’s minimum operating load is 25% of the boiler’s full capacity (100% capacity divided by 4). A 10:1 turndown means the minimum operating load is 10% of the full load capacity (100% capacity divided by 10). Why is Boiler Turndown Ratio Important? Turndown ratio is important for boilers that are required to operate at a wide variation of capacities. A boiler with a higher turndown ratio will usually handle fluctuating loads more efficiently than one with a low turndown. A boiler’s burner will modulate or “turn down” as the demand for hot water or steam decreases, in an attempt to meet only the required load. The turndown ratio tells you the minimum output the boiler can handle before turning off and then cycling on and off frequently. If the demand goes below the bur
Marine Engineering exam notes for Seafarers