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RATIO – Sets the desired change in system water temperature increases as the outdoor
temperature decreases. The reset ratio is expressed as follows:
2:1 for every 2 degree change in outdoor temperature the sytem temperature will change
1 degree.
Temperature °F
e.g: Set = 135°F Ratio Outdoor System
2:1 60 140
40 150
20 160
Suggested Guidelines
Typical Reset Ratio Setpoint at Design Temp:
Temp@ Temp@
RADIATION Design Cond 70°F 40°F 20°F 0°F -20°F
Standing 190 105 0.3:1 0.6:1 0.8:1 1.1:1
Convection or
Baseboard 200 105 0.3:1 0.5:1 0.7:1 0.9:1
Fan Coil - Heating 190 105 0.3:1 0.6:1 0.8:1 1.1:1
Fan Coil - Heat & Cool 140 105 0.9:1 1.4:1 2.0:1 2.6:1
Radiant Floor 120 105 2.0:1 3.3:1 4.7:1 6.0:1
Radiant Ceiling 120 105 2.0:1 3.3:1 4.7:1 6.0:1
SUGGESTED GUIDELINES
The selection of the correct ratio is dependent on the initial temperature and the desired system
water temperature setpoint and the design temperature conditions.
The reset ratio and setpoint must be selected so that the controller will raise the system water
temperature from the initial setpoint – suggested 110°F – to the maximum temperature required
when the outdoor temperature drops from 70°F to the design temperature.
PUSH SELECT
Design temperature rise of the system related to the boiler. Default value 20°F.
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