How Many BTU’s Does Your Furnace Give You From Your Fuel Source?

BTU’s measure heat units

The common measurement for heat is British Thermal Units (BTU’s), the amount of heat it takes to raise the temperature of one gallon of water 1 degree.

Heat loss is the amount of BTU’s required to heat the structure after deducting the heat that escapes through doors, windows, and roof.

BTU input is simply the number of BTU’s found in an energy source. For example:

- #1 fuel oil has about 125,000 BTU’s in a gallon
- #2 fuel oil has about 138,500 BTU’s in a gallon
- LP (propane) gas has 95,000 BTU’s in a gallon

Furnace efficiencies determine how much heat is captured in your home

BTU output is the efficiency in which your furnace captures these BTU’s when burnt. A gas or oil furnace less than 15 years old, connected to a chimney, is about 80% efficient. The other 20% of energy produced by the furnace goes out the chimney. Gas and oil furnaces must produce this amount of heat to take combustion bi-products out of the home.

A condensing gas furnace, with two or three-inch plastic pipe vents and forced draft fan is about 90% efficient.

The American Gas Association (AGA), Underwriters Laboratories (UL), or other accredited testing facilities certify these efficiencies. The Gas Appliance Manufacturers Association (GAMA) and Department of Energy (DOE) accept these certified results.

Unfortunately, these same organizations do not rate wood furnaces and wood stoves for efficiency.

How efficient are wood furnaces?

Most solid fuel furnaces and stoves are about 30% efficient. Wood and all solid fuels such as coal, corn, and grain have the same 12,000 BTU’s per pound of energy. After deducting water content, heat values of woods have about 8,000 Btu’s of usable energy per pound. This lower efficiency is comprised of various factors:

Wood burns at different temperatures because of the different amounts of water in it. Wet wood burns at a lower temperature and is therefore less efficient because of incomplete combustion.

Forty percent (40%) of the energy in wood is unburned gas released as wood burns. This gas fails to ignite and release its energy because it starves for oxygen. To burn these gases, an injection of a controlled amount of air just above the flame is necessary. This action increases the efficiency of the appliance.

A lot of smoke out the chimney indicates that wood energy is being lost and loss of efficiency.

How does coal measure up?

Coal has virtually no air or water in it.

Coal will not burn unless you provide air to the fire chamber on a continuous basis. If you shut the air off to a coal, the fire will go out.

Coal remains at 12,000 Btu’s per pound because it contains no water.
How does Corn Measure up?

Corn has the same BTU’s per pound as wood. Dried corn with 12% moisture weighs about 56 pounds per bushel. It has about 8,000 usable BTU’s per pound (same as wood). A bushel of corn will provide about 448,000 BTU’s. If a corn furnace is 70% efficient, it will deliver about 31,360 BTU’s of heat into your home. The heat loss in an average 3-4 bedroom home with reasonable insulation is about 25-30,000 BTU’s per hour on a winter day. You can check your heat loss with a heating professional or utility company. It would take about 6 bushels a day to provide the same amount of heat as a gas or oil furnace.

Other Interesting Facts

- The EPA sponsored a meeting in Portland several years ago where it was determined that fireplaces were about 1% efficient.

- Wood pellets are generally very expensive compared to a wood log. There are about 8,000 BTU’s per pound of usable energy in either one.

- The answer to inefficient Wood furnaces is Central Heating using Multi-fuel or Combination Wood/Gas, Wood/Oil or Wood/Electric Furnace

Multi-fuel and combination fuel central heating furnaces come with optional air conditioning, electronic air cleaning, and/or humidifier. Two side-by-side thermostats control these furnaces. The homeowner can burn wood as a primary fuel, using the gas or oil burner to ignite. When the wood burns down, the gas or oil burner takes over to keep the home comfortable. The Yukon-Eagle brand furnace has a massive heat exchanger (firebox), a secondary air system that burns the smoke and unburned gases, and a large circulating blower. These furnace components make this furnace extremely efficient and use a fraction of the amount of wood of an outdoor boiler, other wood furnaces, stoves, or indoor boilers without these features. The Yukon-Eagle Multi-fuel wood is UL Listed (approved) to heat your home with wood or coal without electricity.

Yukon Eagle has been manufacturing and distributing wood furnaces for many years and is the industry leader in multi-fuel and wood burning furnaces. Located in Minnesota, where the winters can test a heating system, we have learned how to do it right.