you need warmth the most wenn it's cold. So you need a candle more wenn it's cold out there, than wenn it's hot out there. If it's cold out there, than it won't melt. So why not make a modulair kit ? If it's cold, keep the candle. If it gets hot, get the alternative's in the kit. Or beter, just fish out the candle and have alternative's already in the kit.

just my 2 cents