By Thad Warren
Your air conditioner is the Cookie Monster of appliances. Instead of cookies, your AC gobbles electricity. Me want electricity!
If you live in a warm climate like Texas, 30-40% of your electric bill is from your AC. Howdy yall.
Gut check. A standard 3,000-watt AC running 12 hours a day costs $112 a month. For reference. You can lease a brand new Nissan Leaf for $103 a month.
The idea of my AC costing anywhere near as much as a car is insane.
At the same time, there is no way I can live without an air conditioner in the summer. Making small changes like turning up the temperature setting doesn’t save a whole lot. Albeit something.
Shopping for an AC is your biggest opportunity to set yourself up for long-term energy savings. Lower your electricity bill. Great! Reduce your carbon footprint. Sweet.
Important Note: This article deep devices into central AC units. Not window units. You can find info and recommendations for window units here.
Buying an AC is not simple. You can not (or should not) buy and install your own central AC. There’s a 100% chance you will screw it up. Hire a professional.
Same with the purchasing process. Every home and application is different. Find a reputable AC company and let them help you.
Your AC Company will:
Get ready to open your wallet. The average cost to install new AC is about $6,000. So expect to spend $4,000 - $8,000.
Have more than one unit? You guessed it. It’s going to be more expensive.
There are a bunch of other costs that can stack up as well. Ductwork, wiring, new thermostats, and a bunch of other things you haven’t thought about.
It is important to install the right size equipment for your home in order to get the best performance and comfort. You need the right cooling capacity for your square footage.
A system that is too large will not keep your home comfortable because it will cycle on and off too frequently.
Your contractor can verify the proper size for your home using a tool called "Manual J." Higher efficiency equipment with variable speed compressors does a better job of compensating for any oversizing.
Air conditioners are complex systems. Luckily Energy Star has efficiency ratings that manufacturers submit so that we can gauge how efficient a unit is.
But it’s not that simple. It’s not just the “ac unit” that needs to be efficient. Your ductwork plays a huge role. Leaky ductwork means reduced efficiency.
Other factors about your home will cause your system to be more or less efficient. Things like home much shade your home gets. If your outdoor condensing unit is in the shade. How much insulation your home has.
Air conditioner efficiency measures how well a system cools a given space and the amount of electricity needed to do so.
Two main measures of air conditioner efficiency:
Seasonal Energy Efficiency Ratio (SEER) - SEER ratings are equal to the cooling output of a system divided by its overall power consumption during the cooling season (i.e., the warm part of the year).
Energy Efficiency Ratio (EER) - EER is similar except it measures the “instantaneous” efficiency rather than over an entire season.
One other term to be familiar with is the British thermal unit (BTU). It’s often referenced when measuring cooling capacity.
BTU stands for British Thermal Unit. One Btu is the amount of heat required to raise one pound of water by one degree Fahrenheit. BTU/hr is used as a benchmark for the capacity of an air conditioning system.
Window units use EER, while central air conditioning systems use both SEER and EER. The higher the SEER and EER ratings, the more energy-efficient the system.
You can also consider an air-source heat pump in place of an AC-only system. Heat pumps can be used for both heating and cooling. In cooler weather, they perform exactly like air conditioners. Come winter, they are the most energy-efficient heating method for home heating.
Side by side a heat pump and an air conditioner look identical. That’s because a heat pump is an AC. In the summer it works exactly the same.
The difference between a heat pump and an AC is that in the winter the heat pump absorbs heat from outside and pumps it into your home so it can be distributed by your furnace as heat.
But wait, isn’t it cold outside? Yes. Heat pumps are designed to pull heat from outside even in extremely cold temperatures. Even if it’s 10 degrees outside, a heat pump can generate heat from outdoors.
This video walks through the difference between a heat pump and an AC system:
The biggest benefit of heat pumps is that they use electricity instead of natural gas to heat your home.
There is a potential downside. If electricity is more expensive than natural gas in your area the heat pump is not cost-effective. If you’re not sure you find the average electricity rate in your state here.
You will likely buy your new unit from the local installer, or from the manufacturer. In either case, you probably make the purchase based on their recommendation. They will handle the logistics and installation.
If energy efficiency is what you're looking for, you should point that out. To give you some baseline data here is a chart to show you the most energy-efficient model of various sizes.
Air conditioning units provide cooling to a space by transferring heat from inside to outside and by blowing cool air inside.
There are 8 main components that AC units use to keep your home cool.
When you trigger the AC to turn on via the thermostat, the compressor turns on and pumps refrigerant. The compressor turns the refrigerant from a low-pressure low-temperature vapor into a high-pressure high-temperature vapor.
The refrigerant then passes through the condenser. The big thing with all the coils outside your home. The vapor condenses in and releases the heat outside. The large fan on your outdoor unit helps move air over the coils.
It leaves the condenser and goes back into your home as a medium-temperature liquid to the metering devices. Usually a thermal expansion valve.
When the liquid passes through the metering devices its temperature reduces significantly. The now cooled refrigerant flows through the evaporator coil.
The blower turns on and begins moving air through the house. Warm air is sucked in via the return duct. It then goes through a filter. The filter blocks dust and other nasty stuff from recirculating.
The warm air passes through the evaporator. The evaporator coils that are full of cold refrigerant cool the air that is blown back into your home.
Here’s the crazy part. The air causes the refrigerant to boil. Once it boils it turns into vapor. The vapor then goes back out to the condenser where it will go through the entire process again.
This video illustrates the process in more detail:
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