Adding another Heating Cartridge: FIRMWARE

Hello all,

I am in a capstone that is designing and manufacturing a print head that will mix to filaments. Our heating block is quite big, roughly 25x25x40 mm (LxWxH), and the one 24 volt 40 watt heating cartridge is not providing enough heat to heat the block. We constantly get the “Heating Failed” error. I have modified the firmware so that it will present this error if it does not raise one degree in 40 seconds.
I would like to modify the firmware to add another heating cartridge so it will provide sufficient heating and at a reasonable rate. can you guys help?