AFUE and Oil Boiler Facts

AFUE Ratings are Not Accurate, Determine the Real Efficiency

AFUE Ratings Are Not Accurate

Boiler rating or boiler efficiency is typically measured by Annual Fuel Utilization Efficiency (AFUE). AFUE ratings are not accurate.

Determining The Real Efficiency (Oil Boilers)

To determine the real oil boiler efficiency, use our interactive illustration by placing your mouse over the specific boiler area. [ View Gas Boiler Version ]


Typical Tankless
Coil Boiler
“High Efficiency”
Cast Iron Boiler

System 2000
AFUE Rating 82% – 87% 86% – 87% Up to 87%
Real Efficiency 56% – 59% 56% – 62% Up to 85%
Draft Regulator YES YES NO
Jacket Insulation ¾” to 1″ sides & top ¾” to 1″ Up to 4″
Base Insulation No – boiler sits directly on floor No  YES insulated plus
boiler mounting stand
Outside Air for Combustion No Optional YES
Energy Saving Control Not applicable
or not an option
Additional Cost and requires trial and error adjustments Energy Manager for combined heat and hot water standard on all systems. More efficient than indoor/outdoor reset controls
Integrated Hot Water System Coil in boiler for hot water or electric Coil in boiler (tankless coil) or indirect tank High performance hot water storage tank with integrated control


When the government created AFUE (Annual Fuel Utilization Efficiency) ratings, they had a good plan. However, AFUE ratings don’t help consumers make educated decisions about a hot water heating system’s efficiency because it only measures some chimney related losses. It’s like saying highway driving is the miles per gallon you’ll get all year when you know you’ll be doing most of your driving around town.

It’s time the heating industry had an accurate way to measure efficiency.

AFUE remains a misleading indicator that should be improved with an index that truly measures a hot water system’s efficiency. The heating industry needs it. The homeowner deserves it. Once you’re able to accurately compare different heating system’s efficiency,