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Proper System Sizing

Proper System Sizing

How do I ensure that my air conditioner/heat pump is properly sized for my Central Florida-area home?

A heat pump is simply an air conditioner that cools in the summer and heats in the winter by reversing the flow of refrigerant in the heating mode. When we discuss sizing a heat pump, we are really referring to the heat pump’s air conditioning side. The sizing technique is identical between a heat pump and an air conditioner. When it comes time to replace your existing heat pump system, most air conditioning and heating contractors will use your existing system size as the primary guide in selecting a replacement.

If the existing system worked properly and provided proper heating and cooling levels for your home, then this may be a logical solution.  However, to properly size the system, we perform what is called a load calculation (Manual J).

Sizing is strongly influenced by your climate, but several other factors affect the size of the unit required, including the amount of wall and attic insulation you have; the types and placement of windows and doors; and the orientation of your home to the sun. To work most efficiently, a heat pump’s heating and cooling capacity has to match your home’s heating and cooling demands. An undersized system won’t adequately cool your home, while an oversized one won’t dehumidify properly and can make the house feel drafty in the winter.

Examining these factors can also alert you to the possible benefits of upgrading the insulation in your home. By making your home more energy efficient, you may be able to reduce the size of the air conditioner you need.

Sizing the Unit

Air conditioning size is expressed either in tonnage or BTU per hour (BTU/h). One nominal ton equals 12,000 BTU per hour. Why is proper sizing so important? An undersized system won’t be able to cool your home properly on the hottest days and will cost more to operate because it has to run longer than a system that is sized correctly.

An oversized air conditioner consumes more energy because it requires more electricity to run a bigger unit. An oversized air conditioner doesn’t lower humidity effectively. That’s because it cools the air so quickly that it cycles off before it has a chance to circulate the proper volume of air through the system to remove the moisture that makes us uncomfortable.

The result is a room that doesn’t seem as cool as the temperature indicates. In fact, the room can feel clammy and damp. This is why we always recommend a thorough evaluation of the cooling and heating requirements of your home prior to purchasing a new system.

When sizing an air conditioning system for your home, we begin by determining the required cooling capacity just as we would with any air conditioning system. Heat pumps are simply an air conditioning system that efficiently heats in the winter. They are offered in the same tonnage increments as you expect from standard air conditioning, so pick the proper tonnage based on the cooling requirements of your home.

Call us at 407.459.8916 for a free, thorough evaluation. A home comfort advisor will visit your home and provide a detailed sizing analysis of both the heat pump and supplemental heating element.

Once the sizing requirements for the cooling side of your heat pump system are determined, we then need to select the proper supplemental heating element that is included with all of our heat pumps. If you are replacing an existing heat pump system, simply locate your main breaker panel and identify the indoor heating unit breaker. Look for a number where you grasp the breaker. Various breaker sizes and the corresponding heating elements are shown below:

  • 30 amp – 5.0 kW
  • 40 amp – 7.5 kW
  • 50 amp – 8.0 kW
  • 60 amp – 10.0 kW
  • 80 amp – 15.0 kW
  • 110 amp – 20.0 kW

If you are not replacing an existing heat pump system, you can use the heating element sizing guidelines below.

Supplemental Heating Element Sizing for Central Florida Area Systems:

  • 1.5-ton to 3.0-ton Heat Pump — Use a 5 kW
  • 3.5-ton to 5.0-ton Heat Pump — Use a 10 kW

*Remember, the sizing above is informational only and not is intended to replace proper sizing conducted by a professional.