How to Determine House Heating Tonnage

Window units and ductless air conditioners are rated by the BTUs as opposed to tonnage.

Evaluating the heating and cooling needs of a house results in purchasing the proper sized unit which enables greater control over accurate climate control and minimizes the impact to the electric bill. HVAC (Heating, Ventilation, Air Conditioning) units are measured in tonnage. The measurement of tonnage is a direct relation to the BTUs (British Thermal Units) required to pull or add heat to the air inside of a house. Calculating the BTUs is a simple conversion of square footage.

Things You'll Need

• Measuring tape
• Calculator

Instructions

1. Measure each room that will be impacted by the unit for length and width. Include all areas of the house excluding those rooms that will not be connected to the unit, such as basements, attics, and closets. Maintain the measurements for each room separately even if the room is directly tied to another, such as an open-floor plan kitchen and living room.

2. Convert the square footage to BTUs. 100 to 150 square feet converts to 5,000 BTUs. Convert 150 to 250 square feet to 6,000 BTUs. 250 to 350 square feet converts to 7,000 BTUs. Multiply any measurement by 25 for sizes over 350 square feet. Add 1,000 BTUs to every bathroom or laundry room and 4,000 BTUs for kitchens.

3. Add each individual BTU measurement together to arrive at a total BTU measurement for the house.

4. Convert the total BTU measurement to tonnage by dividing the measurement by 12,000. Round the result to the next highest 5 tenths. For example, a measurement of 4.1 tons rounds to 4.5 tons. A measurement of 3.6 tons rounds to 4.0 tons.

References

• Consumer Energy Center: Window Air Conditioners
• Alpine Home Air: Selecting Air Conditioner Size