A spa wax warmer with the temperature set on High usually takes up to 10-15 minutes to fully heat a 14 oz. wax can and larger cans take slightly longer. Note that hard wax takes longer to melt than soft wax so, if you want to heat both types of wax simultaneously, make sure your double wax warmer has separate temperature knobs for each warming well. Once the wax melts, stir it and lower the temperature to keep the wax warm, but not burning hot.