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A heat transfer system comprises a plurality of cells, a plurality of heating elements, and a controller for independently controlling the plurality of heating elements. The heat transfer system is capable of maintaining a fluid temperature within a predetermined range. A second pump pumps fluid thr

A heat transfer system comprises a plurality of cells, a plurality of heating elements, and a controller for independently controlling the plurality of heating elements. The heat transfer system is capable of maintaining a fluid temperature within a predetermined range. A second pump pumps fluid through a heat exchanger in operative relationship with the blower upon a call for heat.

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1. A heat transfer system comprising: a first cell (46) storing liquid and a second cell (48) storing liquid;a first heating element assembly (56, 66) associated with the first cell and a second heating element assembly (58, 68) associated with the second cell, wherein said first heating element ass

1. A heat transfer system comprising: a first cell (46) storing liquid and a second cell (48) storing liquid;a first heating element assembly (56, 66) associated with the first cell and a second heating element assembly (58, 68) associated with the second cell, wherein said first heating element assembly (56, 66) comprises a first tubular coil (66) situated about a first heating element (56), said first coil adapted to receive liquid from a heat exchanger (14) and to heat the received liquid before it is introduced into said first cell (46) and said second heating element assembly (58, 68) comprises a second tubular coil (68) situated about a second heating element (58), said second coil adapted to receive liquid from a heat exchanger (14) and to heat the received liquid before it is introduced into said second cell (48);a controller (22) adapted to independently energize each of said heating element assemblies (56, 66; 58, 68) when the temperature of liquid in the associated cell is below a first predetermined temperature; anda first pump (50) adapted to pump liquid from the first cell (46) to a heat exchanger (14) and from the heat exchanger to the first cell (46) via the first coil (66) and to the second cell (48) via the second coil (68), and a second pump (52) adapted to pump liquid from the second cell (48) to said first cell (46) in order to maintain a liquid temperature in said first cell (46) above a second predetermined temperature,wherein the liquid comprises a heat transfer oil which is liquid at temperatures of 220-250° F. and wherein the heat transfer system comprises a closed flow circuit for the liquid. 2. The heat transfer system of claim 1, wherein the first heating element assembly (56, 66) and the second heating element assembly (58, 68) are adapted to heat liquid before the liquid is pumped to the heat exchanger (14) and as the liquid returns from the heat exchanger to at least one of the cells (46, 48). 3. The heat transfer system of claim 2, wherein second pump (52) is adapted to pump liquid from the second cell (48) to a bottom area (46a) of said first cell (46). 4. The heat transfer system of claim 2, wherein each heating element assembly (56, 66; 58, 68) is adapted to preheat liquid before it mixes with liquid in the respective cell (46, 48) and substantially simultaneously heat liquid in the respective cell (46, 48). 5. The heat transfer system of claim 1, wherein each of said coils (66, 68) comprises an outlet (66a, 68a) situated toward a bottom area of the respective cell (46, 48). 6. The heat transfer system of claim 1, wherein said controller (22) is adapted to energize said heating element assemblies (56, 66; 58, 68) in a predetermined order. 7. The heat transfer system of claim 6, wherein said controller (22) is adapted to alternately energize said heating element assemblies (56, 66; 58, 68) when a temperature in at least one of the cells (46, 48) falls below a first predetermined temperature of 230° F. 8. The heat transfer system of claim 7, wherein upon a call for heat, said controller (22) is adapted to cause said first pump (50) to pump liquid through said heat exchanger (14) and said controller (22) is adapted to alternately energize said heating element assemblies (56, 66; 58, 68) after a temperature of said liquid in at least one of said cells (46, 48) falls below said first predetermined temperature. 9. The heat transfer system of claim 6, wherein said controller (22) is adapted to alternately energize both of said heating element assemblies (56, 66; 58, 68) when a liquid temperature in at least one of said cells (46, 48) falls below a minimum predetermined temperature of 220° F. 10. A heat transfer system, comprising: a heat exchanger (14);a blower (16) in operative relationship with said heat exchanger;a liquid tank (30) having a first cell (46) and a second cell (48), each cell containing a liquid comprising a heat transfer oil which is liquid at temperatures of 220-250° F.;a first pump (50) adapted to pump liquid from said first cell (46) to said heat exchanger (14) and from said heat exchanger (14) to said first cell (46) and said second cell (48);a second pump (52) adapted to circulate liquid from said second cell (48) to said first cell (46);a first heating element assembly (56, 66) situated in said first cell (46) and a second heating element assembly (58, 68) situated in said second cell (48), wherein said first heating element assembly (56, 66) comprises a first tubular coil (66) situated about a first heating element (56), said first coil adapted to receive liquid from the heat exchanger (14) and to heat the received liquid before it is introduced into said first cell (46) and said second heating element assembly (58, 68) comprises a second tubular coil (68) situated about a second heating element (58), said second coil adapted to receive liquid from the heat exchanger (14) and to heat the received liquid before it is introduced into said second cell (48);at least one sensor (70, 72) adapted to sense a temperature in at least one of said first cell (46) and said second cell (48);a thermostat (20) operable to set a desired room temperature; anda controller (22) coupled to said thermostat (20), said first pump (50), said second pump (52), said blower (16), said first heating element assembly (56, 66) and said second heating element assembly (58, 68), said controller (22) operable to respond to said thermostat (20) and to control said first heating element assembly (56, 66) and said second heating element assembly (58, 68) and said second pump (52) in order to maintain a temperature of said liquid in said liquid tank (30) within a predetermined temperature range. 11. The heat transfer system of claim 10, wherein said controller (22) is adapted to alternately energize said first heating element assembly (56, 66) and said second heating element assembly (58, 68) when a temperature sensed by said at least one sensor (70, 72) is less than or equal to a first predetermined temperature. 12. The heat transfer system of claim 10, wherein said controller (22) is adapted to energize at least one of said first heating element assembly (56, 66) or said second heating element assembly (58, 68) and said second pump (52) to maintain a temperature of said liquid in said second cell (48) and said first cell (46) within said predetermined temperature range. 13. The heat transfer system of claim 10, wherein said controller (22) is adapted to alternately energize said first heating element assembly (56, 66) or said second heating element assembly (58, 68) and said second pump (52) to maintain a temperature of said liquid in said second cell (48) and said first cell (46) within said predetermined temperature range. 14. The heat transfer system of claim 13, wherein said controller (22) is adapted to alternately energize said first heating element assembly (56, 66) and said second heating element assembly (58, 68) for a two minute period of time. 15. The heat transfer system of claim 13, wherein said controller (22) is adapted to simultaneously energize each of said first heating element assembly (56, 66) and said second heating element assembly (58, 68) when a liquid temperature falls below a minimum temperature. 16. The heat transfer system of claim 10, wherein said controller (22) is adapted to energize said first pump (50) and said blower (16) in accordance with a predetermined impulse cycle and in response to a thermostat setting. 17. The heating system of claim 10, wherein said controller (22) is adapted to energize said first pump (50) and said blower (16) independent of said first heating element assembly (56, 66) and said second heating element assembly (58, 68). 18. The heat transfer system of claim 10, wherein said controller (22) is adapted to alternately energize said first heating element assembly (56, 66) and said second heating element assembly (58, 68) if a temperature sensed by said at least one sensor (70, 72) falls below a predetermined lower operating temperature, until a temperature of said liquid reaches a predetermined upper operating temperature. 19. The heat transfer system of claim 18, wherein said predetermined lower operating temperature is 230° F. and said predetermined upper operating temperature is 250° F. 20. The heat transfer system of claim 10, wherein said controller (22) is adapted to simultaneously energize each of said first heating element assembly (56, 66) and said second heating element assembly (58, 68) when a temperature of said liquid in said second cell (48) or first cell (46) is less than or equal to a minimum temperature. 21. The heat transfer system of claim 10, wherein a dividing wall (36) separates the first cell (46) and the second cell (48) and the dividing wall (36) is provided with at least one opening (40) in a lower portion of the dividing wall (36). 22. The heat transfer system of claim 10, wherein the second pump (52) is operable to deliver liquid from an upper portion (48a) of the second cell (48) to a lower portion (46a) of the first cell (46). 23. The heat transfer system of claim 10, further comprising a safety liquid level control (74) operable to monitor the liquid level in the liquid tank (30), wherein the safety liquid level control (74) is coupled to the controller (22) and is operable to generate a low level signal to the controller (22) if the liquid level drops below a predetermined minimum liquid level, and wherein the controller (22) is operable to turn off the first pump (50), the second pump (52), and the heating element assemblies (56, 66; 58, 68) when it receives the low level signal from the safety liquid level control (74). 24. The heat transfer system of claim 10, wherein liquid level in the first and second cells (46, 48) is between a minimum liquid level (80) and a maximum liquid level (82). 25. The heat transfer system of claim 10, wherein a wall (30e) of the first cell (46) is provided with a plurality of baffles (84) operable to facilitate circulation of liquid toward the first heating element assembly (56, 66) as the liquid is introduced in the first cell and before the liquid is delivered to the heat exchanger (14).