What Size Air Conditioner Do I Need for My Home?

In order for your air conditioner to do its job properly, its cooling output must match the operating conditions in your household. An AC unit that’s too small won’t have a sufficient cooling capacity, while a unit that’s too big can easily provide too much output. Several critical factors affect the size of the air conditioner that works best for your home.

What Does AC Size Mean?

In air conditioning terms, the word size refers to the maximum amount of cooling power a unit can put out in a single hour. In turn, this power is measured by the ton. However, tons of cooling capacity differ from tons of weight. An air conditioner has a one-ton capacity if it puts out 12,000 BTUs per hour. (A BTU is the amount of energy needed to make a pound of water hotter by a single degree on the Fahrenheit scale.) Most residential ACs in the U.S. have a 2-ton rating. Heavier duty units have a 3-ton rating.

Factors That Affect Your AC Size Requirements

The factors that affect your AC size requirements are complex and interacting. They include the overall volume of your home’s conditioned space, your home’s age, the number and position of your home’s windows, the condition and age of your home’s windows and the quality of your home’s interior sealing. They also include the quality and suitability of your home’s ducting network, your home’s typical level of sun exposure, the degree of shade protection provided by shrubs and trees on your property, the surface area of the outdoor walls that receive sunlight and the efficiency rating of the new AC unit you plan to install.

Use the “Manual-J” Standard

Professionals in the HVAC industry rely on a calculation commonly known as “Manual-J” to determine the right size of air conditioner for a given building. In brief, this calculation uses an analysis of all the relevant factors to arrive at the optimal AC size or tonnage. A “Manual-J” analysis can be done on a whole-house or room-by-room basis. As a general rule, HVAC specialists rely on the whole-house approach if you plan to keep the ducting network already in place in your home. However, some experts call for a more detailed room-by-room analysis even when you don’t intend to replace your ducts.

Call Your HVAC Specialist

Reputable HVAC specialists in your area should be familiar with the “Manual-J” standard and know how to use that standard to calculate the AC tonnage needs for your home. The specialist you choose should also know how to incorporate the efficiency rating of any new air conditioner into the size equation. In addition, a qualified HVAC professional should be able to install the unit you purchase.
For additional information on best practices for air conditioner installation, make sure to check back with us often.