High efficiency vs. Low/Medium efficiency Furnace

high efficiency furnace

Low efficiency furnace is less than 75% efficient. However, the federal government now requires residential gas-fired furnaces to have a minimum efficiency of 80%. Medium efficiency furnaces are between 80-82% efficient. High-efficiency furnaces (also called condensing furnaces) have AFUE ratings that range from 90% to about 97%. These furnaces have a secondary heat exchanger where the moisture in the escaping flue gases is condensed. This phase change from water vapor to liquid water releases heat, improving the unit’s efficiency.

What is annual fuel utilization efficiency (AFUE)

AFUE is a laboratory procedure used to measure the efficiency of a furnace. This calculation accounts:

-        Heat losses up the chimney

-        Heat losses through the appliance jacket

-        Heat losses due to on-and-off cycling

But it does not account for:

-        Electricity use (fan energy use)

-        Heat lost through the distribution system (ductwork)

What is a furnace?

furnace

A furnace is a heating system which can use natural gas, oil, firewood or propane for its fuel. However, natural gas is the most common form of fuel used in North America.

What is annual fuel utilization efficiency (AFUE)

AFUE is a laboratory procedure used to measure the efficiency of a furnace. This calculation accounts:

-        Heat losses up the chimney

-        Heat losses through the appliance jacket

-        Heat losses due to on-and-off cycling

But it does not account for:

-        Electricity use (fan energy use)

-        Heat lost through the distribution system (ductwork)