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AC Unit in California

What Size Air Conditioner Do I Need for My Home?

Finding a replacement AC system for your Murietta home is both exciting and intimidating. You look forward to cooler days as well as the potential for saving on your energy bills each month. Most homeowners in Southern California focus only on staying within budget, but this may not provide the ideal solution in every case.

At We Care Plumbing, Heating and Air, we recommend that homeowners in the area take a more balanced approach by considering both up-front costs and the cost of operation. There are several factors that affect these.


When you look at a certain air conditioning model for your home, you will see information about how many BTUs the unit produces under ideal conditions. BTUs are British thermal units that indicate the cooling capability of the AC. One BTU equals the amount of heat (energy) needed to warm 1 pound of water by 1 degree Fahrenheit.

For AC systems, this indicates the amount of heat that is removed from the indoor environment to keep it cool during the summer. The BTUs also let you know how much heat the unit will produce during the cooling process. You may also find units that are labeled in tonnage. One ton for an AC unit equals 12,000 BTUs.


Another abbreviation that you will come across when shopping for a new AC unit is AFUE, or annual fuel utilization efficiency. The AFUE tells you how much of the energy is used for actual cooling compared to what is lost during operation. For a unit with 90 AFUE, 90% of the energy is used specifically for cooling your home, and the remaining 10% is lost through the exhaust and ventilation to keep the unit running safely and efficiently.

SEER Rating

Seasonal energy efficiency ratio (SEER) was introduced by the U.S. Environmental Protection Agency (EPA) as part of laws intended to protect the environment. SEER tells you how much cooling is produced by a unit during a typical summer. Under federal law, manufacturers are required to meet the minimum SEER rating for the region in which the AC unit is being sold.

The EPA sets the minimum standards. Higher SEER ratings let southern California homeowners know that a unit is very efficient and will use less energy than a similar unit with a lower SEER rating. The key to understanding SEER ratings is that they represent operation under ideal conditions. If Murrieta has an unusually warm summer, the unit may be less efficient. During cooler summers, the unit may be more energy efficient.


Watts are an interesting way to size an air conditioner for your home. Manufacturers typically do not label their equipment with watts, so you may need to do a bit of math. Watts represent the rate at which power flows through the system. Calculate the watts by multiplying the volts and amps on the label.

Once you have this number, convert it into kilowatts. This tells you how many kilowatts the unit uses per hour. Next, look at your most recent utility bill from the electric company. Multiply the rate on the bill by the kilowatts per hour. This gives you a general idea of how much you will spend each month during the summer to cool your home.

Square Footage

Square footage is an important factor for choosing the right size AC system for your residence. Most homeowners know the total square footage, but you are not cooling every square foot of your home. Unused spaces, such as closets and garages, do not need to be considered.

Take the total square footage and subtract any areas that are not connected to your heating and cooling system. This is the baseline square footage to use when buying a new air conditioner.

Normal Use

Ratings on residential AC systems reflect normal use in a typical household. If you tend to like your home cooler or slightly warmer in the summer, you should factor this into your purchasing process. You may be able to buy a lower capacity unit if you don’t need as much cooling, or you may need a slightly larger unit if you like the indoor temperature to be closer to chilly.

Family Size

The number of people who live in your home affects how well your AC system performs. More bodies mean more body heat, especially as spaces get smaller. If you only have one or two people living in your home, you can go by the information on the packaging of the AC unit. If you have more than two people, you may need to look for a higher-capacity AC system.

Appliances and Electronics

Do you live a relatively simple life without a lot of electronics, or do you love modern convenience, gadgets and toys? All the appliances and electronics in your home generate heat to some degree. This heat may be a secondary result of operation such as heat from an oven, or it could be intrinsic to the nature of electronic devices such as computers and stereos. The more appliances and electronics you have, the greater capacity you need in a new cooling system.

Insulation Quality

The insulation of your home prevents warm air from coming inside and cool air from escaping to the outdoors. If you have an older home, or if you see cracks and openings around the doors and windows, your AC system is going to need to work harder to maintain comfortable temperatures in the summer. This means that you will need a higher-capacity AC unit. You may be able to get by with a lower-capacity system if you invest in new insulation and sealing the doors and windows.

Existing Equipment

Modifying existing ducts and heating equipment to suit a new AC system can be costly. You want to make sure that your new AC will fit with what you have already. If you are concerned about your new cooling system fitting with the existing equipment, call We Care Plumbing, Heating and Air. Our technicians know how to properly size air conditioning systems for all types of configurations.


Last, but certainly not least, is your budget. The up-front costs for a new cooling unit can overextend your budget, so you should strive to stay within it as much as possible. This is why we recommend that you work with We Care Plumbing, Heating and Air before buying a new AC unit.

Our technicians know how to size cooling systems and ensure that you get the most for your money. They also explain how to calculate return on investment through energy savings and discuss upgrades that can reduce energy use in your home.

Are You Looking For a New Home AC System?

Since 2000, We Care Plumbing, Heating and Air has provided homeowners in Murietta and surrounding areas of Southern California with the peace of mind they need. Our installation, repair and maintenance services keep your AC, heating and plumbing performing at top efficiency. We also help homeowners find the best new equipment for their budget and family comfort.

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