WPPO Hot and Cold Tumbler With Lid ( 4 pack ) Remii (9) The optimum heat transfer Toscana (9) The optimum heat transfer efficiency is for the low burn rate (using HHV) and represents the appliance’s ability to convert the energy contained in the wood logs into energy transferred to the room in the form of heat and does not take into account the chemical losses during combustion and local air quality programs offer their own rebates or incentives for high efficiency wood and pellet appliances — these vary by location and change frequently The sleek charcoal gray color goes well with the rustic look of your wood fired meals These vacuum insulated tumblers keep your drink at the perfect temperature for hours