Learn & Understand

From Hearth to Central Heat: A History of Warming the Home

The efficient furnace hidden in a modern basement is the endpoint of a long quest to heat a home without filling it with smoke or squandering fuel. From open fires to sealed combustion, the history of home heating is a story of steadily capturing more warmth from every unit of fuel — the very idea that furnace efficiency measures today.

The Open Fire

For millennia the hearth was the heart of the home: an open fire whose warmth was welcome but wildly inefficient. Most of its heat vanished up the chimney along with the smoke, and it warmed only those huddled directly before it. The open fire was better than nothing, but it wasted the overwhelming majority of the fuel's energy.

The Enclosed Stove

A great leap came with enclosing the fire in an iron stove. A closed firebox radiated heat from all its surfaces into the room rather than losing it up an open flue, and clever designs routed the hot exhaust through longer paths to extract more warmth before it escaped. The Franklin stove and its successors captured far more of the fire's energy than any open hearth.

Central Heating

The next transformation moved the fire out of the living space entirely. A central furnace or boiler burned fuel in one place and distributed the warmth throughout the house — by heated air through ducts, or hot water and steam through radiators. Heat became something delivered to every room evenly, and the fire itself disappeared from view.

Squeezing Out the Last Heat

Modern high-efficiency furnaces push the ancient quest to its limit. A furnace's rating — its AFUE — measures how much of the fuel's energy becomes useful heat rather than escaping in the exhaust. Condensing furnaces extract even the heat in the water vapor of combustion gases, wasting little. The gap between a furnace's fuel input and its heat output is exactly the inefficiency that centuries of design have worked to close.

General educational background only. Refrigerant handling and combustion appliances are regulated and can be hazardous ÔÇö this work should be done by a licensed, certified technician.

Sizing the Furnace

To estimate furnace input size from a home's heat loss and AFUE, use the Furnace Size Calculator. Compare the cooling side with the HVAC Load Calculator, or weigh a heat pump alternative with the Heat Pump Sizing Calculator.