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Choosing the right furnace: Tonnage & BTU

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Use these terms to help you pick out a proper furnace

When shopping for a heating system, you will note that a new furnace label will refer to Btu’s, while air conditioners are sized by tons. Heating contractors determine the size of a heat pump or furnace you need based on the size and location of the home and these figures. Traditional heating systems include furnaces and boiler systems, while geothermal heating and heat pumps are increasing in popularity due to their long-term efficiency and lower operating costs.


BTU is an acronym for British Thermal Units. This is the heat required to raise the temperature of one pound of water one degree Fahrenheit at sea level. MBH is thousands of BTUs per hour, so a furnace rated at 100,000 BTUs may be listed as 10,000 MBH if it were 100% efficient. Efficiency is figured based on the input, in this example 100,000 BTU, and the output, for instance, 80,000 BTU. This would be an 80% efficient unit. These figures help determine the amount of energy that will be required to operate the unit.


Tonnage is figured for air conditioning systems, which include geothermal heating units. The term is derived mathematically from the amount of energy required to melt one ton of ice during the course of a day. That figure is slightly less than but averaged at 12,000 BTUs per hour per tonnage. For example, a heat pump that is ranked at one ton would remove 12,000 BTUs of heat from the home in one hour.

Energy Efficiency

An efficient heating system significantly reduces the cost of operation while heating and cooling the home. Geothermal units take advantage of the stable temperature found underground. The closed system loops below the ground, heating water, and then bringing it back to the heating source for optimization. This means the boiler is heating water that is starting at an already warmer temperature and thus is operating more efficiently. The reverse occurs in the summer when heat is released underground and naturally cooled before traveling back into the home. Most ground temperatures range from 45 degrees to 55 degrees, providing a year-round stable starting point.

Installing an efficient new heating system will help lower monthly bills while keeping your home warm and cozy. Call Agers Heating and Cooling today to learn more about our traditional furnaces and geothermal heating units and learn which works best for you.

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