FAQs – Home Air Conditioning Information

When you first shop for a new air conditioning system, you’ll notice that AC units come in a range of sizes. To choose the right size, calculate the square footage of the area you would like to cool. Unless your home has unusually high ceilings, multiply this figure by 25 to get a rough estimate of the cooling power your air conditioner must have. Air conditioner manufacturers measure cooling power in British Thermal Units per hour, or BTU. You might also see BTU converted to tons on units; 12,000 BTU is equal to one ton of cooling capacity. Tons are to air conditioners as horsepower is to engines; the term refers to how many tons of ice your home would need to provide equivalent cooling power.

Other factors also influence your home’s cooling needs. If you have soaring ceilings or large windows that let sunlight stream in, you may need to move up in cooling capacity. Rooms that contain appliances or heat-producing equipment may also need more cooling to feel comfortable. To get the most accurate measurement, call an HVAC contractor and request a full load calculation be done for your home.

An undersized air conditioner can’t cool your home efficiently or comfortably and could cost you more in utility bills than a properly sized unit. On the other hand, an undersized unit cycles on and off too quickly to remove all the moisture from the air, leaving your home feeling humid.

The alphabet soup of acronyms you see when choosing a new air conditioner can seem intimidating at first, but these figures are key to your unit’s efficiency and the air quality it provides. Two closely related terms, EER and SEER, are related to a concept you already know: BTU.

Both the Energy Efficiency Ratio (EER) and Seasonal Energy Efficiency Ratio (SEER) measure how much cooling power you get from your system for the wattage it consumes. Mathematically, SEER is equal to the system’s BTUs per hour divided by the average watt usage for the season. The same relationship holds true for EER, but this rating provides a snapshot rather than an overall measure of energy efficiency. A higher SEER means a more efficient system that delivers more cool air per watt. New AC systems must have a minimum SEER of 13, according to the U.S. Department of Energy. Commercially available systems can have SEER ratings as high as 25 or 26.

Another acronym you might see is MERV, which stands for Minimum Efficiency Reporting Value. This rating refers to the unit’s effectiveness at filtering the air and maintaining consistent air quality. A higher MERV rating means the system filters smaller particles; a lower rating permits larger particles to pass through the system’s filters. The highest commercially available ratings range from 13 to 16 and filter bacteria, smoke, ground pigments and other fine particles. Most home units range from 9 to 12 MERV ratings and can remove household dust, hairspray, mold and auto emissions from the air.

If you have recently bought your home, check with the previous owners. They may have warranty paperwork saved in a folder. For older homes or systems without papers detailing warranty information, look on the interior or exterior unit for a date of manufacture. Most manufacturers’ warranties on central air conditioners are for at least five years, but some may be longer or include extended warranties. Warranty information varies widely by manufacturer and installation service, so look for a service number on the unit to find more information.

While it isn’t always necessary to replace the interior portion of your AC unit when upgrading your exterior unit, it is often the most economical choice in the long term. By replacing both parts of the central air conditioner at once, you ensure that the entire system is under the same warranty. Upgraded systems also offer greater energy efficiency, especially when they work in conjunction with a more efficient exterior unit. With a matched system, you don’t risk the compromises that replacing parts piecemeal can sometimes create.

It’s sometimes possible to replace only half the system, especially if you retain the same brand name throughout the system. Before opting for a partial replacement, check with installation specialists who can break down the pros and cons of your specific system with you. Doing half the job is no bargain if it limits your system’s efficiency and quality in the long term.

No single system is best across the board. Each cooling system has its advantages for specific climates, households and cooling needs. Instead of crowning one system as king, it’s better to think of the three possibilities as equals and select the one that fits your needs.

Heat Pump Characteristics

Reaches peak efficiency in temperate climates
Can heat and cool your home with a single economical system
Removes humidity efficiently
High initial installation costs
Low operation costs

Central Air Conditioning Characteristics

Provides outstanding cooling power in any climate
Can be customized for specific climates with dehumidifiers or humidifiers
Efficient at improving overall air quality through filtration and recycling
Economical installation and operation
Acts as a ventilation system with a fan-only option on temperate days
Quiet operation

Your air conditioner’s life span depends on a variety of factors, but a central AC unit typically lasts for about 15 to 20 years. Some units are still functional after three decades or more; however, these older units no longer cool efficiently and cost far more to operate than contemporary models with higher SEER ratings. Proper maintenance, moderate temperatures, short summers, a non-smoking household and other factors also contribute to a unit’s longevity.

An assessment from an HVAC specialist can give you an idea of how much life your old air conditioner has in it and can also estimate any possible savings you might get from upgrading the system. Follow these tips to extend the life of your air conditioner:

Change filters monthly
Keep the external unit clear of debris
Clean the condenser coils and evaporator coils seasonally
Vent heat and humidity from cooking or bathing to save wear on your AC

Comfortable temperatures are only one part of maintaining high air quality in your home. Your air conditioner also wrings excess moisture out of the air, inhibiting mold growth and increasing comfort. The filtration system removes particulates such as pollen and pet dander to put people with asthma and allergies more at ease.

Depending on your climate, you may not need heating or air conditioning often. With a quality ventilation system, you may be able to give your air conditioner a break until full summer. Moving air feels cooler than still air even without temperature control, lowering your energy bills and letting you take advantage of pleasant spring and fall weather. Your AC system’s fan can double as an air circulation system, but you can help it along with vents and ceiling fans. State-of-the-art energy-recovery ventilators, or ERVs, dehumidify air and use exhaust heat to pre-condition air.

On the hottest days of summer, it’s tempting to bump the thermostat as low as it can go, but the wear on your air conditioner and the high energy bills you’ll face are probably not worth it. At the other end of the extreme is keeping the temperature so high that your AC only comes on a few days per year; this tactic can lower your utility bills, but it could leave you with a mold problem from poor ventilation and too much humidity.

The best setting for your thermostat is the point at which your comfort and your air conditioner’s energy efficiency overlap. Typically, that point lies somewhere between 76 and 80 degrees Fahrenheit, although it may be lower in humid coastal climates. A programmable thermostat can be a significant cost-cutter because it lets you adjust the temperature from hour to hour to find the best mix of comfort and economy. Depending on how you use it, a programmable thermostat could save you between 10 and 20 percent of your heating and cooling costs.

Your air conditioner normally cycles on and off to hold the temperature constant while maintaining energy efficiency. If it didn’t cycle off occasionally, your home would soon feel more like the inside of your refrigerator. However, rapid cycling is not normal and could signify one of a number of issues. Most of these problems have easy solutions.

An outdated thermostat may be giving your AC unit false signals. Older control units with failing mercury switches or poor temperature recognition can tell your air conditioner that it’s far warmer or cooler in the home than it is, leading to rapid on-off cycles. Replacing the faulty thermostat with a digital version or a programmable control panel quickly brings your air conditioner to its senses again.

Sometimes the mixed signals come from somewhere other than your thermostat. Ice forming on evaporator coils can cause the system to cycle rapidly. Turning the unit off and allowing the coils to de-ice is a temporary solution, but call a certified HVAC technician to find out why the coils are icing in the first place.

If your air conditioner is new and short-cycles constantly, you may have an oversized AC unit. If the air conditioner cools a space too quickly, it shuts off before it has fully conditioned the air. The temperature may be low, but the humidity remains, making the air feel clammy and leading to rapid cycling. The alternative is to go to a smaller unit.

All air conditioners dehumidify the air as they cool it. The water vapor that used to be in the warm, unconditioned air condenses on air conditioner parts. Under normal circumstances, drains remove the excess water, but under some circumstances, water overflows and creates a leak. Excess water typically means a clogged drain somewhere in the system. Under normal circumstances, condensation drains from a drip pan into pipes that carry it into the home’s sewer system or to an exterior outlet. Over time, rust particles, dust, soil or other material can form a clog and force the drain pan to overflow.

Another possible cause of leaking is a tilted drain pan. Normally, the pan that catches condensation from the evaporator coils is level or tilts toward the drain, but it can be disturbed and tipped away from its usual position. When this happens, the fix is simple: Replace the pan where it belongs.

Any leak warrants prompt attention from an air conditioning repair technician. If left alone, leaks can cause significant water damage to plaster, wallboard, carpeting and furnishings.

Air conditioners are designed to cool, but sometimes their coils can freeze up completely. Under normal circumstances, air moving over evaporator coils carries enough warmth to exchange its heat with the chilled coils. Without sufficient air movement, the water that naturally condenses on the coils then freezes; once this process starts, ice can quickly build up and freeze coils solid. Your air conditioner is designed to shut off when the coils are frozen, so short-cycling may be a sign to check your coils for ice.

Freezing coils could mean an obstruction in your system’s filtration system or a problem with the blower that restricts air flow over the coils. Low coolant levels can also cause freezing; with lower coolant pressure in the coils, they become colder and freeze condensation before it can drip away and collect in the drain pan. Let a frozen air conditioner thaw completely before turning it on again. Call a specialist to uncover the reason for the freeze.

Unless something damages your air conditioner’s closed coolant system, you probably don’t need to have the refrigerant in your AC replaced. However, even a tiny leak can eventually deplete your system of coolant. If you suspect a coolant leak, notice freezing up of your system or feel less cool air coming from vents, choose a certified HVAC specialist who can replace the refrigerant and repair the leak. Refrigerant types vary by make and model, so replacing coolant is a maintenance job for the professionals.

Like any sophisticated piece of machinery, your air conditioner benefits from the occasional tune-up. A technician will change filters, check drain pans, clean coils, lubricate compressor parts and monitor coolant levels to keep your AC in top shape. When your air conditioner gets regular maintenance, it runs more efficiently, saving you money on utility bills. You also extend its life with proper care and reduce the likelihood of a midnight emergency call to a repair specialist. Proper maintenance locates small problems before they grow into big ones and keeps your air quality as high today as it was when your system was newly installed.