Turndown vs. Valve Position

The Meaning of “Fire Rate” on the C-More Controller

AERCO boilers and water heaters feature turndown ratios up to 30:1, the highest of which are unmatched in the marketplace – far exceeding the 3:1, 4:1, 5:1, 6:1, 8:1, and 10:1 capabilities of competitive units.

Competitive boiler designs typically rely upon variable speed blowers and off-the-shelf gas valves to drive BTU/hr. input. In contrast, AERCO units feature a unique air/fuel delivery system, including patented gas plate designs, which support stable combustion control over a far greater range of operations.

Sometimes, competitive sales reps who are unfamiliar with our advanced technology have disputed our turndown claims by incorrectly referencing program settings displayed on our C-More unit controllers and in our O&M manuals.

In our manuals and on our standard controller, FIRE RATE refers to an air/fuel valve position (% open) on the particular model of AERCO equipment. Because each model has a unique gas plate, the BTU/hr. input rate associated with this valve position/fire rate varies by model. Consequently, our standardized controller reports on valve position – not BTU/hr. input.

The charts in the below PDF outline the relationship between (1) A/F valve position, (2) BTU input level, and (3) percent of unit capacity for our Benchmark series.

Download charts PDF


The Importance of Turndown

Turndown is the ratio of maximum fuel input rate to the minimum fuel input rate of a variable input burner.

In general, it refers to the ability to adjust a boiler's or water heater's firing rate (input) to precisely meet the real-time heating demand (output) of the system without temperature overshoot or wasteful cycling.

Less fuel burned as a result of modulating input and heat transfer is also enhanced when units operate at part load. Click here for more.