@Rasoul Salehi
First, I don’t use an electric heater. At the moment I have no such desire to use that as the very sight of wires, switches, etc. seem alien to me. Second, charcoal doesn’t disturb me at all. I can easily sense and smell what is being heated.
Well, Sandal emits quite fine aroma if heated, not burnt. Even a few granules or chips will do. First, I heat Frankincense, and let it burn entirely. Frankincense resin creates a layer on the charcoal. Moreover, till then, the chunk of coal develops enough ashes that reduce its strength. Then I place an Oud chip to heat. Moderate temperature liberates aroma present inside the chip. When the chip gets fully burnt, I wipe the residues of Oud away, and here comes Sandal. When I place granules on the layer of frankincense, Sandal wakes up from its slumber. No quick burning at all. No smoke at all. Just wafts of Sandal and just Sandal. I heat Sandal chips at least three times, and it takes pretty long time. Chips never gets black when I place them last time. But aroma gets more subtle and lasting. Frankincense layer is a kind of stabilizer. Thus, I prefer it.
It depends upon experience how to handle the charcoal. Sometimes, I miss heating Oud chips, and goes directly to Sandal. But it all depends upon my senses to measure the strength of temperature.
I have mixed Ceylon Sandal in Rose Wax. It emits unique aroma. No citrusy or lemonade Rose notes at all, nor does the aroma of dry petals, but Ceylon Sandal and Subcontinental Rose metamorphosed into an aged Sandal Rose blend aroma being carried by the evening air. It is Keats’ Dejection an Ode. But ‘sweet heartache’ it is.