The Heating Coil stores FE, which allows it to be used as Furnace fuel.
By default it can store 1,500,000 FE, and uses 50 FE to provide 20 ticks of fuel. For comparison, a piece of Coal provides 1,600 ticks of fuel.
Heads up!
For technical reasons, it only works when used in Furnaces, or other block entities that extend the AbstractFurnaceBlockEntity class.
Obtaining
Red Coal can be obtained by passing Iron Bars through a Resonator, which costs 16.0 GP.
Configuration
The FE capacity, FE usage, and fuel duration can all be configured.