Hi. Can anyone answer the following? For the case of the TRANE 14-15 SEER line of 3-31/2 Ton Heat Pumps coupled with the appropriate variable or fixed speed air handler, and requisite outdoor thermostat’s; Is there a 10Kw resistance element which can be staged to operate at either 5Kw or 5Kw +5Kw? Is there a 15Kw assembly which could be set up to give 5Kw or 10Kw? I was told the TRANE 10Kw heater is all on or all off which seems non-optimal from an energy use standpoint.