Frequently Asked Questions about MA High Efficiency Air Conditioning

Learn how to select a contractor, how air conditioners are sized and more.

How do I select the right contractor?
  • System sizing and proper installation are critical to energy efficiency and home comfort. It’s important to hire a qualified contractor who uses Manual J or an equivalent size calculation tool. If your contractor is certified by North American Technician Excellence (NATE), you know they’ve received special training about how to size and install your system.
    Note: NATE certification is not required for customers to receive rebates.
  • Resources for finding a contractor:
  • COOL SMART Participating Contractors
  • Air Conditioning Contractors of America
    Phone 888-290-2220 Fax 703-575-4449
    http://www.acca.org/consumer/
  • North American Technician Excellence (NATE)
    Phone 877-420-NATE
    http://www.natex.org
How are air conditioners typically sized to meet the cooling needs for my home?
  • Your comfort while using air conditioning depends both on reducing air temperature and removing humidity. An air conditioner should ideally run for 20 minutes or more on each cycle to cool the indoor air and to reduce humidity.
  • Oversized air conditioners run in short inefficient cycles. They waste energy since they must run for a few minutes at the beginning of every cycle just to cool down the indoor coil and ducts. Only then can they can cool and de-humidify your home. That original cool-down energy is wasted after the air conditioner shuts off.
What is meant by “BTU” and “Ton?”
  • An air conditioner's ability to remove heat is expressed in BTUs (British Thermal Units) per hour,or "tons" of cooling. Each ton equals 12,000 BTUs per hour, and is equal to the energy contained in a ton of ice, a term left over from the days when buildings were cooled with ice. Your air conditioner should have a ton of cooling capacity for every 400 to 1,000 square feet of floor area, depending on your home's energy efficiency and your local climate.
How does insulation affect my cooling needs?
  • A poorly shaded home with little insulation and lots of air leaks might need a ton of air conditioning for every 400 square feet of floor area. A well insulated and well-shaded home with few air leaks might only need one ton per 1000 square feet.
  • Contractors size air conditioning systems using computer programs or extensive hand calculations. To ensure correct sizing, ask your contractor to show you the written calculations for your home. Then have them install the smallest size air conditioner capable of cooling your home.
What is the difference between EER and SEER?

EER (energy efficiency ratio) is a measure of how efficiently a cooling system will operate when the outdoor temperature is at a specific level (usually 95° F). A higher EER means the system is more efficient. You can calculate kilowatts if you know the EER and the size, in tons.

  • EER = BTUs of Cooling @ 95F / Watts used @ 95F
  • In the case of a 10 EER, 2 ton air conditioner: 10 EER = 24,000 BTUs Out / 2,400 Watts In
  • For the same size unit, but rated at 12 EER: 2 EER = 24,000 BTUs Out / 2,000 Watts In or 20% more efficient.
  • If you want to calculate kilowatt-hours, just multiply the "Watts In" by the number of hours that the air conditioner is running.
  • SEER (seasonal energy efficiency ratio) is a measure of efficiency over an entire cooling season, as opposed to a single outdoor temperature. Residential units are almost always rated in SEER. SEER came into use as a more practical measure, since the temperature outside is not always 95º F. Also, the denominator is in watt-hours, not in watts as is the case for EER. The same relationship holds ... a higher SEER means the system is more efficient. SEER is the total amount of cooling the air conditioner will provide over the entire cooling season divided by the total number of watt-hours it will consume or:
  • SEER = Seasonal BTUs of cooling / Seasonal watt- hours used
What is the importance of EER?
  • There are many goals and benefits of utility sponsored Efficiency Programs. Among these is education for the purpose of using energy wisely. From this a rating system to establish standards for energy consumption has been developed.
  • One way to measure energy consumption is Seasonal Energy Efficiency Ratio (SEER). SEER is a measure of efficiency over an entire cooling season. SEER ratings are useful in determining the amount of energy used and the amount of energy saved. Often, the unit of measure associated with SEER is kilowatt-hours (kwh). A kilowatt is 1000 watts used for 1 hour. SEER = Seasonal BTUs of cooling / Seasonal watt- hours used.
  • There is more to energy consumption than kwh. Another measure of energy (and thus energy efficiency) is demand. Demand is the maximum amount of electricity used by an air conditioning system. This usually occurs at start up. The unit of measure associated with demand (or peak) is Energy Efficiency Ratio or EER. EER = BTUs of Cooling @ 95F / Watts used @ 95F. Almost all air conditioning units are tested under the same controlled and specific laboratory conditions to determine the EER rating.
  • Your local sponsors, and the country as a whole, are concerned about using energy efficiently. Efficient usage occurs both in the seasonal and peak arenas. Many advocacy partners in the industry recognize SEER alone does not address demand savings. Use of EER as an industry standard is in an attempt to for continued improvement in demand performance.