With a westinghouse high efficiency heater % of the dollar spent on heating is properly used to heat the home that is real savings! upgrade your existing heating system with the combi wall and see how much you can save! Looking for an environmentally friendly product? the combi wall is for you! this energy star ® certified boiler has an annual fuel utilization efficiency (afue) of up to % while homeowners with older gas furnaces may only be using as little as % of.