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RESET RATIO
The Reset Ratio setting determines how much the Target Temperature will increase as the
outdoor temperature drops. The Reset Ratio is expressed in the following manner:
X:Y X - change in outdoor temperature
Y - change in Target Temperature
The first number in the ratio refers to the change in outdoor temperature in degrees Fahren-
heit below outdoor cutoff while the second refers to the change in the computed Target
Temperature in degrees Fahrenheit. A Reset Ratio of 2:1 means that for every 2°F drop in
outdoor temperature from 70°F, the Target Temperature will increase 1°F.
For example:
Assume a Reset Ratio setting of 2:1 and a Set Point of 120°F.
When the outdoor temperature drops from 70°F to 20°F, the Target Temperature will in-
crease from 120°F to 145°F. (With an outdoor to target ratio of 2:1, a 50°F outdoor tem-
perature decrease results in a 25°F Target Temperature increase). See Reset Ratio Chart
(pg. 20) for more information.
The Reset Ratio is adjustable from 0.12:1 to 8.0:1.
Recommended Initial Setting for Reset Ratio is 1:1.
19
Suggested Settings
The selection of the correct ratio is dependent on the initial temperature Set Point and the desired system water temperature. If the building
is too cold, move the ratio knob counter-clockwise one setting. After a change is made to the ratio, wait several days and evaluate the
comfort level before making another change.
RADIATION
Temp @
Design Cond.
Temp. @
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
Typical Reset Ratio Setpoint at Design Temp:
CONTROL FUNCTIONS