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Air Conditioners: A Guide to Choosing the Best

By Tobias Roberts Rise Writer
Sep 14, 2020

Choosing the best air conditioner for your home is a critical strategy for reducing your overall carbon footprint. Landscaping strategies can offer natural solutions for lowering your home's cooling load, but upgrading to an energy-efficient AC unit should be high on your list of priorities. Are you thinking about replacing your furnace or have an upgrade on your list of potential home improvement projects? If so, here is what you need to know about how to choose the best air conditioner for your home.

hot day

Why Should I Care About My Air Conditioner's Age and Efficiency?

Our world is becoming hotter due to global warming; heatwaves are becoming longer and more intense during the summer months. With this, more and more households increase their energy use to keep their homes pleasantly cool, even as outside temperatures rise into the triple digits. Statistics released by the Energy Information Agency (EIA) in 2018 found that air conditioners account for around 12 percent of total residential energy usage in the US. However, that percentage will continue to rise with each warmer year.

Yale University finds that US air conditioning demand could increase by 59 percent by 2050. On a worldwide scale, the International Energy Agency (IEA) projections predict an increase to 5.5 billion air conditioning units by 2050. This rise amounts to an astounding increase of almost 300 percent. Within the next three decades, the world's population could be using upwards of 6,205 Terawatt Hours (TWh) of electricity to stay safely cooler in a hotter world. This energy use will amount to an enormous quantity of carbon emissions. It will also pose significant challenges to electrical grids that increasingly rely on renewable sources of energy. For context, to get an idea of this rising scope in demand, ten new air conditioners are expected to be sold every second for the next thirty years worldwide.

However, central air conditioning units are major energy hogs and routinely use between 3,000 and 5,000 watts per hour. Homes that have poor insulation or a leaky building envelope will have much higher cooling loads. During the hot summer months, air conditioning expenses will most likely be the most expensive part of homeowners' energy bills.

How Long Do Air Conditioners Last?

As with most household appliances, older air conditioners tend to be much less efficient. Air conditioners are generally built to last for two decades or so. With these increases in efficiency from newer technology, it is worth considering replacing your AC unit sooner. Depending on the unit you have in place, an early replacement can provide environmental AND economic benefits.

When Should an Air Conditioner Be Replaced?

The US Department of Energy states that homeowners may save between 20 and 40 percent of their cooling power costs by replacing older units for ten-year-old air conditioners. The average homeowner spends about $300 each year on air conditioner repairs. Suppose an essential element of your AC unit breaks down. In that case, it most likely makes more economic sense to invest in a new unit instead of investing thousands of dollars on an already outdated model. Even if your older air conditioner continues to function without problems, an upgrade to a more recent and more efficient model might make sense.

For example, air conditioners ten years old (or more) will most likely have a Seasonal Energy Efficiency Ratio (SEER) rating between 8 and 9. Today, the most efficient models on the market can achieve a SEER rating of up to 25. We will explain these efficiency ratings for air conditioning units in more detail in the next section. However, as a general rule of thumb, if your current air conditioner has a SEER rating under 10, you should consider upgrading to a more efficient model. The energy savings alone will lead to quicker payback periods through drastically reduced energy consumption.

Homeowners will most likely benefit from a new air conditioner if their current HVAC equipment is oversized. In the past, many HVAC professionals operated under the assumption that "more power is inherently better." However, oversized air conditioners are not able to function optimally from an energy efficiency standpoint. Not only do larger units require more energy to operate, but they also often cool home interiors far too quickly. This problem leads to what is known as "short-cycling," wherein your AC turns on and off too frequently, thus increasing energy demand.

XC25 Air Conditioner. Photo Credit: LENNOX

What Do Air Conditioner Efficiencies Mean?

As mentioned in the section above, air conditioners' efficiency ratings are measured by the Seasonal Energy Efficiency Ratio (SEER). Essentially, the SEER rating measures the ratio of the cooling output of an AC unit over a typical cooling season. This number is then divided by the total amount of energy the AC unit uses in Watt-Hours. The higher the SEER rating, the more energy-efficient the AC unit. For example, the Lennox Signature Series XC25 Air Conditioner achieves an impressive SEER rating of up to 26, while many older models will be under 10.

Even slight increases in SEER rating, however, can lead to significant energy savings. Kobie's free online SEER energy savings calculator allows homeowners to see for themselves the potential energy savings that come from upgrading to more efficient AC units. For example, upgrading from a 9 SEER to a 19 SEER on a 3-ton air conditioner could lead to 53 percent energy savings per year or a ten-year savings of $8,247.

How Do I Know What Size AC Unit I Need? 

Unfortunately, many HVAC companies and contractors continue to oversize the AC units they install in homes. One way to avoid this common mistake is for homeowners, or an energy auditor, to calculate the optimum-sized AC unit for their family. Remember, you can achieve the best efficiency, therefore lowering operating costs by taking into account the area the unit must cool alongside heat loss and heat gain considerations. For this, we offer two quick, rule of thumb calculations that any homeowner can use.

How To Calculate The Cooling Load

Begin by calculating the size of the space that the AC unit will be expected to cool. This will require you to multiply the length times the width of the room (or rooms) serviced by this AC for window units. You will most likely use your home's total square footage for central units unless you have attics or basements that are not cooled. Then, multiply that number by 25 BTU, and this will give you a general estimate of the size of the AC unit you need.

For example, a 2,000 square foot home multiplied by 25 BTU will mean that a 50,000 BTU central AC unit is estimated. There are, of course, other considerations to take into account, such as the average summer temperature, the efficiency of your home's insulation, and the quality of your building envelope. However, this initial calculation can give homeowners a baseline to begin their research.


How To Calculate Heat Gain

You can use this simple calculation to find the expected heat load of your home in BTU by multiplying the length (ft.) x the width (ft.) x the height (ft.) x 4. A home's heat gain comes from people inside the house, heat-producing appliances like dryers and refrigerators, open doors and windows, and solar radiation from the sun entering through windows and under-insulated walls and roofs. Air conditioners can only effectively cool a home if its output is greater than the heat gain, as measured by BTU.

For an air conditioner to cool a room or building, its output must be greater than the heat gain. It is vital before purchasing an air conditioner that a heat load calculation is performed to ensure it is big enough for the intended application. For example, a 12-foot by an 18-foot living room with 10 foot high walls would have an estimated heat gain of 8,640 BTUs. A window AC unit for that living room, then, should be between 10,000 and 12,000 BTUs.

Should I Trust My Contractors Sizing Estimate?

Using the calculations outlined above, homeowners should have a general idea of the proper size for a new AC unit. Perhaps a contractor is trying to sell you a 75,000 BTU central air conditioner when your calculations led you to believe that you only need a 50,000 BTU unit. This discrepancy serves as a red flag and a sign that you should consider getting a second estimate (which never hurts!). However, HVAC professionals specializing in energy auditing can offer much more exact calculations based on your home's specific context and construction.

Amana AVXC20 Air Conditioner
AVXC20 Air Conditioner. Photo Credit: Amana

What Questions Should I Ask My Contractor Before Committing?

Before making any final decision about upgrading to a new AC unit, you should ask your AC contractor the following questions:

  • What is the SEER rating of the proposed unit?
  • How did you size the air conditioner you recommend?
  • Might I opt for a smaller unit if I invest in other energy-efficiency upgrades to my home?
  • What might other technologies, such as a smart thermostat, make this new AC unit more efficient?
  • How often do you recommend preventative maintenance on this unit?
  • Is short cycling a potential problem with this size of the AC unit?
Energy Star Certified AC Unit Home Depot
Energy Star Certified AC Unit. Photo Credit: Home Depot

What AC Units Are the Most Efficient?

Homeowners can choose to invest in smaller air conditioners that are only designed to cool certain parts of your home to reduce the electricity demand from air conditioning. Many people spend the bulk of their time in the living room, dining room, or kitchen. However, central air conditioning units will distribute the cold, conditioned air to every part of the home, including unoccupied bedrooms and basements. So, central air drastically increases the house's overall energy demand, even when nobody enjoys all the pleasantly cool rooms. Window air conditioners operate efficiently and reduce your energy usage. In regions with mild or short summers, a window unit might be the best option.

Whether you choose a window air conditioner or a central AC unit, Energy Star certified air conditioners are the best option. Energy Star certification will mean that the units have higher seasonal energy efficiency ratio (SEER) and energy efficiency ratio (EER) ratings for central AC units. Energy Star certified models use at least eight percent less energy than conventional new models. Check out Energy Star's annual ranking of most efficient air conditioners here.

Remember, higher SEER ratings = lower cooling costs!

Mini-Split Heat Pump
Mini-Split Heat Pump

Should I Replace My AC Unit With a Heat Pump?

Switching to a heat pump might be the most energy-efficient choice for effectively cooling your home. The US Department of Energy recommends this transition for homes located in climates with moderate heating and cooling needs. This energy-efficient alternative can replace both central furnaces and AC units. Like a refrigerator, air-source heat pumps use electricity to move heat from a cooler to warmer spaces using refrigerants.

While a heat pump is most likely more expensive than a new AC unit, it should be cheaper than purchasing both a new AC unit and a new furnace - before even calculating the expected energy savings. You can read the Rise heat pump guide to learn more about switching to a heat pump for your home's heating and cooling needs.

Disclaimer: This article does not constitute a product endorsement however Rise does reserve the right to recommend relevant products based on the articles content to provide a more comprehensive experience for the reader.Last Modified: 2021-06-21T09:50:00+0000
Tobias Roberts

Article by:

Tobias Roberts

Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.