Combination, or combi, boilers are among the fastest growing products in the heating-equipment segment—as much as 10 times more in demand than they were 5 years ago. Part of that growth might be attributed to the increased maximum efficiency—as high as 98 percent compared with 82 percent —that manufacturers have achieved.
The tankless appliance is used for domestic water heating and to heat a home. A high-usage natural-gas combi boiler has a uniform-energy factor (UEF) of 0.94 and a high-usage standard-storage water heater operates at 0.64.
Dave Yates, who is the president of contractor F.W. Behler, says switching to a combi boiler from a conventional boiler or water heater can reduce your fuel consumption by 30 percent to 70 percent. “The main takeaway is an ultrahigh-efficient appliance that can replace two low-efficiency appliances [conventional boiler and water heater],” Yates says. Not to be overlooked is the space that’s gained when you replace two appliances with one.
Chris Drew of manufacturer Burnham Holdings says consumers who make the change might experience a delay when they switch to hot water from cold, and they might encounter a limit in how much hot water that’s available to them at a given time. Drew advises that if you get only 3–3.5 gallons of hot water per minute, then you shouldn’t try to operate two showers at the same time.
Yates says he typically recommends that a consumer get a larger combi boiler, so it will accommodate a high demand.