How to Shop for Central Air Conditioning

By Vernon Trollinger, August 29, 2017, Energy Efficiency, Green, Home Improvement, Save Money

While most homeowners love their homes, not every home is perfect. There are one or two things the homeowner would like to change, such as an outdated bathtub for a new walk-in shower or updating the look of their kitchen. And then there’s occasional “uh-oh” of the unexpected repair. We’re going to identify several projects and some of the ins and outs of what you can expect.

How to Shop for Central Air Conditioning | Bounce Energy Blog

How to Shop for Central Air Conditioning

Because your air conditioning system is the largest user of electricity in your home, it’s important to make sure that it’s running at peak efficiency. But like any other appliance, AC systems do wear out over time. If it’s not keeping your home comfortable or you’ve noticed increasing electric bills, you might be facing an expensive breakdown soon. If your air conditioner’s condenser unit (the outside part) or your entire HVAC system is older than 10 years, there’s the possibility that finding some key replacement parts might be difficult. Plus, in 2010, production and importation of HCFC-22 refrigerant was banned. For homeowners who own an older HVAC system that uses HCFC-22 refrigerant, they face steadily rising prices for fixing leaks.

It might be time to start shopping around for a replacement, especially since replacing a 10 year old system with a new energy efficient system could save you 20% to 40% off your cooling energy costs.

SEER and EER

Current federal law requires that all new air conditioning systems use the environmentally friendly R-410A refrigerant (which won’t work in old systems using R-22) and to have a seasonal energy efficiency ratio (SEER) rating of 15 minimum. SEER is a measure of how well the system will perform during the course of a season. The higher the rating, the less energy it will use —roughly 5% less per SEER. For example, an older 12 SEER upgraded to a higher efficiency SEER 16 system will be approximately 20% more efficient. Meanwhile, the Energy Efficiency Ratio (EER) measures how efficiently a cooling system will operate when the outdoor temperature is at a specific level (95° F). Again, the higher the EER, the more efficient the system. Energy Star rated air conditioning systems need to have their EER rated at 12 or better. Some of the best Energy Star systems are rated above 20 SEER and 14 EER which save about 30% over the federal minimum approved systems. While these systems might cost more at the onset, you’ll see lower energy costs as soon as you start using them.

How to Shop for Central Air Conditioning | Bounce Energy Blog

What Size Air Conditioner Do I Need?

It’s not a simple matter of just dropping in any size of air conditioning system. The right size (or capacity) air conditioner will run a proper full cycle, ensuring that your home stays cooler longer. If the system is too big, it will quickly over-cool the air in your home and shut off before the building structure itself (walls, wood, furniture, etc) can cool adequately. Consequently, over-sized systems run for too-short periods but far too often, adding to your electric bill.

Meanwhile, an undersized system will be too under powered to adequately cool your entire home. The system will run continuously, waste energy, and also wind up costing you more.

Air conditioning systems are rated in “tons”. A century ago, ice was used for refrigeration and a little later, air conditioning in railroad passenger cars were able to calculate the melting rate, which was important for keeping cool. For one ton of ice, it takes 286,000 BTUs of heat to melt it completely. Since that is going to happen over time, assuming that rate is constant over a 24 hour period, that results in 11,917 BTU per hour —roughly 12,000 BTUs.

Consequently, 12,000 BTUs equals 1 ton of air conditioning.

To get a very rough estimate of the tonnage you need, you could try out this rule of thumb estimation equation:

[ (Square footage of your home x 25 BTU per square foot) + (the number of people x 400) + (number of windows x 1,000) + (number of doors x 1,000) ] / 12,000 = Required tonnage.

However, while rule of thumb estimates are handy, they’re woefully inaccurate because of better air sealing and moisture control from improved construction techniques as well as changes in HVAC technologies. Because they’re so inaccurate, it’s extremely important to get an accurate and precisely-sized air conditioning system. The HVAC industry relies on using a Manual J load calculation developed by the Air Conditioning Contractors of America (ACCA). Load calculations take into consideration the amount of heat a structure might absorb, which includes:

  • Total volume of the home’s living space.
  • Area of sun-exposed exterior walls.
  • Number, age, condition, and orientation of windows —do your windows face south?
  • Amount of sunshine on your home.
  • Age of your home’s construction.
  • Degree of air sealing
  • Amount of insulation in ceilings, walls, and floors.
  • Existing ventilation system and ductwork.
  • Amount of shade from trees and shrubs.

Professional air conditioning installers should perform a Manual J load calculation to ensure the best possible performance and comfort for the HVAC systems they install. Because air conditioning is one of the most expensive conveniences you can have in your home, it’s important to be able to rely on a trained professional that you can trust to listen to your needs and guide you through this complex process to help design and install the right-sized energy efficient cooling system to work with your home.

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About 

A native of Wyomissing Hills, PA, Vernon Trollinger studied writing and film at the University of Iowa, later earning his MA in writing there as well. Following a decade of digging in CRM archaeology, he now writes about green energy technology, home energy efficiency, DIY projects, the natural gas industry, and the electrical grid.

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