There is no simple equation to decide what size heat pump to put in a 1,800-square-foot home. Instead, there are many factors to consider when sizing your home for heating and cooling. A heat pump that is too small won't cool or heat the house to a comfortable level. A heat pump that is too large runs only a short time each cycle. These short cycles waste energy and cost the homeowner money over time.
How Air Is Cooled
A heat pump works similar to an air conditioner. The machine pumps a liquid into a highly pressurized series of tubes. As the molecules of the chemical become pressurized, they become hotter. A valve releases the pressure quickly and the chemical turns into a gas. The sudden change of form cools the chemical. The air conditioner blows air through the cooled tubes, cooling the air before it enters the home.
How a Heat Pump Works
A heat pump uses both the heated condenser coils and the cooling coils. During the summer, when the consumer needs cool air, the heat pump blows water over the cooling coils of the heat pump. In winter, the unit provides warm air as it blows over the heated condenser coils. Heat pumps replace or assist the home's central heating unit.
How Heat Pumps Are Measured
Heat pumps come in BTUs, which stands for British thermal units. One BTU is the amount of energy it takes to raise a pound of water one degree. When the issue is an air conditioner or heater, the unit is measured in tons. Each ton of heating or cooling capacity is equal to 12,000 BTUs. So a 1-ton heat pump creates or absorbs 12,000 BTUs. A 2.5 ton unit handles 30,000 BTUs, since 12,000 times 2.5 equals 30,000.
Calculating Your Need
A major factor of the calculation is the outside temperature. Homes in a temperate environment work well with a smaller unit. Homes in a cooler area need more heating ability. Figure 35 to 40 BTUs per square foot in warm climates and 55 to 60 BTUs per square foot in very cold climates. Also consider the amount of insulation in the home. Homes with more energy-efficient insulation in the ceiling and walls require less heating than older, less insulated homes.