Back in the days before smart phones, televisions and automobiles, many people living in cold-winter climates cooled their homes and businesses in the summer with blocks of ice, which was harvested by the ton – millions of tons. In relation to cooling by ice and cooling by modern air conditioning, it takes 286,000 BTUs to melt one ton of ice in 24 hours (12,000 BTUs per hour). Over time, the term “ton” came to represent air conditioner capacity of removing 12,000 BTUs of heat from a given space in one hour, not 2,000 pounds of ice.
Manual J: Calculating cooling load
Even though two-ton air conditioner capacity refers to removing 24,000 BTUs of heat from your home in one hour, and not a 4,000-pound A/C, you still need the skills and experience of your HVAC contractor to properly prepare your home for installation and accurately size your new air conditioner upgrade.
Manual J from the Air Conditioning Contractors of America (ACCA) is the best source with which to evaluate your home’s cooling (and heating) load. These are some of the criteria and calculations collected by your HVAC contractor to measure cooling load using Manual J:
- The average temperature, humidity and sun orientation in your part of the Twin Cities metro area
- The layout, square footage and number of floors in your home
- Total number of occupants, energy-usage practices and schedules
- Number and size of windows
- Noting any retrofitted or add-on living spaces
- Rate of air leakage and insulation quality (conducted during the energy audit)
- Consideration of the impact of other HVAC systems, including zoning systems and heat-recovery ventilators
One ton, two tons, three tons or four?
ACCA’s Manual S calculations incorporate the results of Manual J to determine the most efficient size A/C to install in your home. This is an important element in the A/C installation process. In addition to inefficient performance, an over-sized air conditioner will cost more to purchase and install. On the other hand, if you install an A/C with too little air conditioner capacity, it will endure excessive wear and create discomforts such as hot/cold spots throughout your home. It also won’t keep up with cooling during the hottest days.
Whether your home requires two-ton air conditioner capacity, a four-ton A/C or somewhere in between, please contact us at Marsh Heating & Air Conditioning for best results.
Our goal is to help educate our customers in Minneapolis-St. Paul, Minnesota about energy and home comfort issues (specific to HVAC systems). For more information about air conditioner capacity and other HVAC topics, download our free Home Comfort Resource guide.
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