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Tech Tip #6 Most residential furnaces have between 10 KW and 30 KW of resistance heat installed. Usually the total wattage is divided into 5 KW elements, staged by timing relays controlled by a "sequencer." These relays allow some or all of the heat to come on, depending on the model or the controls. The Energy Sentry can control the stages by breaking the low-voltage signals or by controlling each 5 KW element individually via line voltage.
Hook-up (Low-Voltage Control) 1. Refer to the diagram on the furnace and locate the sequencing relays for the heating elements. 2. For a 20 KW furnace (or 2 relays), run a 4-conductor, 10-gauge wire from the control unit to the furnace. For a 30 KW furnace (or 3-relays), run 6-conductor cable. 3. Interrupt the coil wire of the "last-on" sequencing relay in the furnace and wire it through the control unit relay. Most sequencing relays are double pole; thus, 10 KW of heat is controlled by each relay of the furnace. 4. Repeat Step 3 for the "next-on" sequencing relay and wire it through the next higher priority relay of the control unit. 5. With electric furnaces, the load control strategy should be programmed as "fixed priority," in the same order as the loads are controlled by the sequencer. Refer to Tech Tip #13 for information about load control strategy.
Individual Element Control 1. Turn breaker OFF at the furnace. 2. If a Remote Relay Unit is required, mount it in a suitable place on or near the furnace housing. If the furnace is close enough to run conduit or flex between the main control unit and the furnace, make the connections directly at the control unit itself. 3. Interrupt the 1-gauge wires that feed each element and rewire them throught he control unit relay. Use one element per relay if possible (four elements typical). Use two elements per relay if necessary (five or six elements typical). 4. Follow the directions that come with the Remote Relay Unit to hook it to the main control unit. See Tech Tip #10 for information about the Remote Relay Unit. 5. With electric furnaces, the load control strategy should be programmed as "fixed priority," in the same order as the loads are controlled by the sequencer. Refer to Tech Tip #13 for more information on load control strategy. Caution Because most sequencing relays have built-in time delays of an unknown length, it is best to use the "individual element" control method, if possible, for consistently good results. Control of Heat Pump:
Caution In extremely cold regions, it may be necessary to leave the first 5-KW element uncontrolled to avoid having the blower run with all the elements turned off. Another alternative is to connect the first 5-KW element to the highest priority control point, thereby making it the last shed.
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