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Cycle Length
The Cycle Length determines the amount of time that the sys-
tem repeats the heating cycle . The factory default is 60 min-
utes . Depending on the construction and mass of the building,
the cycle length can be adjusted either longer or shorter to
match the building . A brick building has a high mass and may
benefit from a longer cycle length . A wood frame building has
a low mass and may benefit from a short cycle length .
Off
Boiler On
15 minutes
15 minutes
on time
on time
Off
Boiler On
Heating Cycle – Heat On and Heat Off
Outdoor Reset
Outdoor reset is a method of operating a heating system
based on the principle that the rate at which a building
loses heat to the outdoor environment is mostly dependent
on the surrounding outdoor air temperature . As the outdoor
temperature gets colder, the heat loss of the building increases
at a proportional rate . This relationship between heat loss and
colder outdoor temperatures is called a heating curve .
In order to calibrate the control to the heat loss rate of a
particular building, the installer is required to enter the following
heating curve settings .
Outdoor Start Temperature
The Outdoor Start temperature sets the starting point of the
heating curve . This is typically set to start at 70°F (21°C) .
Outdoor Start Percentage
The Outdoor Start Percentage sets the starting point of the
heating curve . This is the amount of heating required when the
outdoor air temperature is at the Outdoor Start Temperature .
This is typically set to operate the boiler at 0% on time .
Outdoor Design
The Outdoor Design sets the end point of the heating curve .
The Outdoor Design should be set to the average coldest
annual temperature recorded in the building area . When the
measured outdoor air temperature matches the Outdoor
Design setting, the control calculates the boiler on time to be
at the Boiler Design % setting .
Boiler Design Percentage
The Boiler Design Percentage is the percent output capacity
of the boiler or steam system required to heat the building
when the measured outdoor air temperature matches the
Outdoor Design setting . The factory default is 100% . If the
building envelope has been upgraded to improve the building
insulation, the existing steam boiler or steam system may be
oversized for the building . In these cases, the Boiler Design
Percentage can be reduced to fine tune the heating curve .
50% On Time With a 30 Minute Heating Cycle
Boiler Off
On
15 minutes
15 minutes
15 minutes
15 minutes
off time
off time
on time
on time
30 minute cycle
30 minute cycle
50% On Time With a 60 Minute Heating Cycle
Boiler Off
30 minutes
30 minutes
30 minutes
30 minutes
on time
on time
60 minute cycle
When an indoor sensor is installed, the control has the option
to automatically change the cycle length to reduce ambient air
temperature swing .
Off
On
15 minutes
15 minutes
15 minutes
15 minutes
off time
off time
on time
on time
30 minute cycle
On
30 minutes
30 minutes
off time
off time
on time
on time
Outdoor = 50°F
Heat Load = 20%
Boiler On Time = 12 min
60 min
Off
On
Off
15 minutes
15 minutes
15 minutes
15 minutes
15 minutes
15 minutes
off time
off time
on time
on time
off time
off time
30 minute cycle
Off
30 minutes
30 minutes
off time
off time
60 minute cycle
Outdoor = 30°F
Heat Load = 60%
Boiler On Time = 36 min
60 min
On
On
Outdoor = 10°F
Heat Load = 100%
Boiler On Time = 60 min
60 min
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