NRP620-9 OMEPAPV20161017 (ENGLISH) REV 1
Page 29 of 42
Summary of Settings & Operation
Draft
Adjustment of the chimney draft controls the rate of burn and has an effect during High and Low fire
operation. Chimney draft must be set between 0.02 – 0.04 inches water column draft during High fire.
The use of a second automatic barometric damper may be necessary on some installations to insure
the precise draft control. A setting of 0.02 – 0.03 inches is ideal. In most installations, the counter
weight on the automatic barometric dampers should be set to the minimum setting.
Refer to the installation and adjustment document included with the draft controller for details.
Timers
There are two timers on the front control panel that regulate system operation. It is
important to note that the RED indicators correspond to the “ON” time, and the GREEN
indicators correspond to the “OFF” time. Typical adjustments are made to the “ON” and
“OFF” time by turning the inner and outer bezels to correspond with the desired duty cycle.
As the timer is in the “ON” and “OFF” state, the associated LED in the upper left hand
corner of the timer is illuminated. The LEDs will illuminate only when that timer is active.
While the timers are identical, they are configured separately to control the system in the
“high” and “low” fire states.
High Fire
Make adjustments to the opening on the combustion blower inlet controls on high fire only. This
opening should be adjusted during the high fire mode of operation to obtain an intense flame that
consumes the fuel at the same rate it is augured in. When using premium wood pellets, start with the
combustion air damper approximately 1/3 open. For other types of fuel, start with the damper
approximately 1/2 open.
Maintain the fuel level in the burn pot between the row of holes halfway up the burn pot and the top of
the burn pot. Best results for efficient combustion and reduction of visible emissions occur when the
fuel is completely consumed just before reaching the top of the burn pot.
The Variable BTU timer relay controls the fuel auger drive rate. Adjusting the Variable BTU Timer
varies the amount of fuel fed from the fuel storage bin into the furnace. By adjusting the “ON” (red
indicator) and “OFF” (green indicator) time, the fuel auger motor duty cycle varies. To determine the
duty cycle, divide the On Time (T
ON
) by the sum of On Time (T
ON
) and Off Time (T
OFF
):
Duty Cycle = T
ON
/ (T
ON
+ T
OFF
)
Adjusting the timers for a higher duty cycle will result in more fuel being augured into the burn pot.
The Variable BTU timer comes set at a 50% duty cycle from the factory; 30 seconds “ON” and 30
seconds “OFF”.
50% = 30 / (30 + 30)
In most cases, setting the timers to the longest time setting that achieves the desired Duty Cycle is
recommended to reduce wear of the electromechanical components caused by start/stop cycling. For
example, setting both the ON and OFF time to 15 seconds produces a 50% duty cycle just as settings
of 30 seconds. However, the 15 second setting results in twice as many start/stop cycles as the 30
