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If you’re considering a new high-efficiency boiler for your home or facility, you condensing boiler 21 11.01.35 AM  should understand the turndown ratio. 

The turndown ratio of a boiler's burner is a key metric. Engineers understand this metric, but most facility managers and property owners need more information to understand the benefits of high burner turndown.

Let's start with how a conventional, cast iron gas boiler operates. The gas burner on a conventional boiler comes on when there’s a call for heat and turns off when the thermostat tells the boiler that the room has reached the setpoint temperature of the thermostat.  Conventional boiler burners operate as either on, or it is off.  There is no in-between.

Condensing boilers,  also known as modulating boilers,  have a burner and burner fan that can change speeds or modulate.  They modulate between on and off.

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 5:1 and 10:1 or even higher.

A 5:1 turndown means the boiler’s minimum operating load is 20% of the boiler’s full capacity (100% capacity divided by 5). A 10:1 turndown means the minimum operating load is 10% of the full load capacity (100% capacity divided by 10).

If a boiler with a 10:1 turndown is capable of a maximum input of 100,000 BTU/H, it means that the unit can actually supply as little as 10,000 BTU/H.  It is also capable of supplying 20,000, 30,000, 40,000, 50,000, 60,000, 70,000, 80,000, 90,000 and what the industry calls “high-fire,” or the maximum 100,000 BTU/H. This is automatic. The boiler’s  control selects the right firing ratio based on system inputs.

A modulating boiler, when properly installed in a well-designed hydronic heating system, can save you a lot of money on energy bills.

A modulating boiler has the potential to run longer cycles.  It is more efficient to run the unit  on low fire for a long time rather than switching on and off at high fire.

Short cycling, turning on at full throttle for a few minutes, satisfying a call for heat, and shutting down again in a few minutes, not only wastes fuel, but it puts stress on the  equipment.  Properly installed, modulating boilers eliminate or greatly reduce short cycling.

If you are looking for a new boiler, you should know that modulating boilers do cost more than conventional boilers the same size. But consider that a modulating boiler's controls are better, and the stainless-steel heat exchangers are more intricate than their cast iron counterparts.

Making a wise choice can help you cut your heating bill substantially. When a modulating boiler is  properly installed by Ohio Plumbing & Boiler, you can  expect the unit to provide energy savings, comfort and a long service life!

Ohio Plumbing & Boiler is the Columbus and Central Ohio leader in residential, commercial and industrial boiler repair, installation and service. Call 614-863-6666 to learn more.

Topics: condensing boilers, turndown ratio