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What Size or Capacity Central Air Conditioning Unit I You Need?

Picking the correct central air conditioning unit for your home is a complicated process. There are several factors that must be considered, both about the air conditioning (AC) unit and the home itself. Each house is different, affecting the cost, efficiency, and quality of of the AC unit in its own unique way. Because of this, many homeowners find the process of choosing a central air unit daunting, but with a little bit of work you can pick the perfect unit for your home.

When it Comes to Your Air Conditioner, Size Matters

It is absolutely crucial that your AC unit is the appropriate size for your home. To ensure you get the right size, contact a professional for a consultation so that all the pertinent aspects of your home are taken into account. A professional considers factors such as the age of the home, square footage and volume of a home's living space, the number and condition of windows, and the existing ductwork and vents.

Both oversized and undersized systems should be avoided. Oversized systems cool the air in your home rapidly, leading the system to shut off before it should. Though the air in the home has been cooled, the building structure itself is not, allowing heat and humidity to seep in and start the system again. This causes the system to run multiple time for too short of a time and the cost quickly adds up. Undersized systems simply do not cool your home properly, causing the system to run constantly which also increases the cost. In both instances, your AC fails sooner and your utility bills are higher than if you'd bought the correct size unit from the beginning.

Understanding AC Sizing Terms

The size of an air conditioner is rated in tons of cooling capacity, with one ton of cooling being equal to 12,000 British thermal units (BTUs) per hour. A standard residential air conditioner is a 2-ton unit, equating to 24,000 BTU per hour. It is important to note, however, that just because two units have the same tonnage it does not mean that they are the same.

Energy efficiency and Seasonal Energy Efficiency Ratios (SEERs) vary from unit to unit. Once you figure out the correct tonnage for your home, consider SEER ratings as you look at different units. Higher SEER rating use less energy, with each SEER using approximately 5 percent less (i.e a 15 SEER unit is roughly 15 percent more efficient than a 12 SEER unit). Central air is one of the most expensive aspects of any home, but installing a unit that's properly sized and has a decent SEER rating significantly reduces those costs.

How to Determine the Correct Size

A truly accurate estimate of the necessary AC unit size for your home requires a professional load calculation, referred to as the Manual J. The majority of installers include this free of charge as a part of their estimate. There are two types of Manual J calculation: room-by-room and whole house.

Room-by-room calculation determines the amount of cooling needed per room, with all results being added together in the end. This is the more accurate method of calculation and is recommended if you are replacing your existing ductwork. Whole house calculation determines the amount of cooling required by the home as a whole. This method is recommended if you are not planning on modifying or replacing your existing ductwork.

It is best to get an estimate from a professional, but that does not mean you can't get a rough estimate of your own.

The equation is: [(house sq. ft. x 25) / 12,000) - 0.5] = required tonnage for your home.

Please note: If you live in an area where temperatures are higher most of the year, you need to add 0.5 instead of subtract it.

While this equation gives you an idea of what unit size you need, it is always more accurate) to consult a professional.

How Much Does a Central Air Conditioning Unit Cost?

Several factors contribute to the cost of central air conditioning, such as the size and type of unit, SEER rating, size of the home, and any additional work that must be done.

  • The average home uses a 13 SEER unit, which costs between $3,000 and $4,000 for an 1,800 square foot house. Remember that the larger the unit, the more it costs.
  • A 2-ton unit has an average cost between $1,500 and $3,000 depending on the SEER rating.
  • A 5-ton unit has an average cost between $2,500 and $7,000 depending on the SEER rating.
  • Installation costs start at about $2,000.
  • Any required ductwork has an average cost of $10 per linear foot, with most houses requiring at least 200 feet worth of work.