Warm will certainly Help growth. Keeping the medium (soil) dark will aid in keeping
the fuzzies and other moody stuff away but the exposed, upper cutting will need some
light. Your cuttings in the furnace room (if not under grow lights) should be in a
window.
What I'm doing now is the clear cup-in-cup method below. The clear cup with holes allows me to check for new roots. Keeping it dark within the second cup seems to prevent the growth of algae, mould or nastiness.
The medium is an off the shelf Fafard seedling mixed with another 50% peat moss to make it drain better. This is working for fairly well right now.
In my next batch I plan to try adding a clear cap to hold in the humidity.