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Save Money Operating Your Air Conditioner, How It Works, Hot Spots and Cold Spots

Don is a retired engineer and shares his experiences and knowledge with his readers to help them as technology gets more complicated.

A Common Sense article.

This article is designed to be informative for the average non-technical reader and explain about your everyday home Air Conditioner. It will show you how to save money operating yours.

There are so many people that have and use Air Conditioners in their homes who really don't have a clue how it works or how to make it work for them at a lower cost.

I asked a friend one day what kind of Air Conditioner they had, and with a confused look in his eye, he said;

"I really don't know, but it works, so I really don't care."

It turns out, his response is pretty standard for a large portion of our population.

Ice Cubes

Some people say that just looking at a picture of Ice or Snow will make them feel cooler.

Some people say that just looking at a picture of Ice or Snow will make them feel cooler.

The Weight of Air when Hot or Cold

One of the first things that you need to understand is the fact that Air, you know, that stuff we all breath, is a gas. So yes, we walk around on our planet in an enormous cloud of gas.

This gas is mostly Oxygen, which is, of course,the part that we all breath and that is one of the many critical things that supports life on our planet.

Now, this Gas that we commonly call AIR, has weight. Air is less dense, and thus lighter when it is warm, than it is when it is Cold.

This basic fact is one reason why you can stand in a typical room and actually feel the difference in the temperature of the Air, at or above your head versus that Air at your feet.

Said another way; Under normal circumstances, Hot Air will rise and Cold Air will drop.

Heating and Cooling Systems and their Ductwork systems

The majority of homes with Heating and Cooling Systems have ducting systems built into the structure that is designed to distribute the Hot or Cold air it generates more evenly throughout the home, thus providing a more even temperature throughout a home for its residents.

Depending on the climate of the area where the home exists, the need for Heating versus Cooling varies. In more northern or cooler climates with longer or more harsh winters, heating is the predominant need.

Because of this, it is more efficient to build a duct system that distributes air at the floor level, simply because, then the Heated Air will rise and provide a more even temperature for the occupants of the room.

Conversely, in a more Tropical climate, there is a predominant need for Cool air.

Because of this, most homes in these hotter climates will have ducts in the ceilings to distribute the cooled Air, which being heavier than the existing warm air, will drop.

A non-Technical Explanation of a Home Cooling system.

Hopefully, I haven't lost you yet with my explanations of air flow.

So, I will move on to give you a simple explanation of how an Air Conditioner works, without getting into any technical jargon; I PROMISE.

Let's look at an Air Conditioning system as two black boxes, each with a fan attached. The boxes are attached to each other with pipes that contain a special gas.

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Step-1: Box-1 is placed outside of the house while Box-2 is placed inside of the house that is to be cooled.

Step-2: When this system runs, the gas is circulated between the two boxes.

Step-3: On the outside box, the gas in the box is cooled and it's fan blows the radiated hot air away from the box.

Step-4: This gas which has now been Cooled is sent via the pipes to the box inside the house.

Step-5: The fan on the inside box blows air by the cooled pipes in the box and into the ducts of the house.

Step-6: The cooled air is distributed by the ducts to the house, thus cooling the interior of the home.

Step-7: The gas in the pipes warms up and is sent to the outside box where the process starts again.

This, very simply, is how an Air Conditioner Cools the air in a home.

Now, there are a lot of very technical things going on in this process including electrical and electronic sensors, and controllers as well as gas Compressors, cooling coils, etc.

But, for the layman, this explanation should suffice for understanding how an Air conditioner actually works..

Home Thermostats

Your Home Thermostat and How it Works.

If I still haven't lost you, consider a few things that you, the resident needs to know.

First of all, your Ducts and the attached vents are designed and installed with the goal to provide, as consistent as possible, a distribution of cooled air throughout the house.

Secondly, You have a Thermostat on the wall of your home, usually centrally located, that turns your Air Conditioner on and off.

That's right, it turns the unit ON and OFF. That's all it does.

But, it also has a temperature sensor that detects the temperature at the wall.

This temperature sensor is designed with a dial or buttons to set it's ON and OFF limit to a specific temperature that you decide is comfortable for you.

For instance if you decide to set the control to 72F, then the Air Conditioner will run until the sensor on the wall detects that it is at a temperature of 72F or lower.

At that point, the switch will open and the Air Conditioner will turn off.

Conversely, when the sensor detects that the temperature at the wall is above 72F, the switch closes and the Air Conditioner is turned ON.

Simple Right? Just an ON/OFF switch that is controlled by a temperature sensor, that you can set.

Hot Spots and Cold Spots

So, at this point, you understand how an Air Conditioner operates and how to turn it ON and OFF.

Using the thermostat, you are able to control the OVERALL and AVERAGE temperature of your home.

Remember, the thermostat senses the temperature of the air at the wall where it is mounted, not in every room of your home. In fact not even the temperature across the same room from the wall where the thermostat is mounted.

Also, remember that the Air Conditioner just RUNS. When it is ON, it provides air that is COOLED. This cooled air is not cooled at different temperatures, it is simply cooled, as best the Air Conditioner can.

So, even though the Thermostat is set to 72F, the air coming out of the ducts is much cooler than this. I am sure that you have noticed this when you stand under one of your Air Conditioning ducts.

And, if you have a window with the sun shining through on one wall, when you walk over there, the air feels a lot hotter. You will find that this is true in the kitchen where you might be cooking (and generating heat) or next to an exterior door that isn't sealed properly.

.So, you see, your home will have Hot Spots and Cold Spots throughout and under varying situations. All you are controlling is the average temperature that reaches the thermostat itself.

How to save money by being smart around your house.

OK, so, how can you save some money using your Air Conditioner?

The following are some sure-fire tips that you can use that will mean significant saving for you when you run your Air Conditioner.

Shades and Blinds

You should keep your Shades and Blinds that are on your windows closed during the periods of the day that the Sun is shining into your windows. The Sun will heat up whatever it hits and this heat is then radiated into your house. This added heat must be offset by your Air Conditioner along with all of the other heat sources that exist.

Doors and Windows

Many newer homes have double-pane glass windows that provide an added level of insulation between the outside and inside temperatures. If you have an older home, and live in a very hot climate, you should upgrading your windows to these newer designs. They can contribute significantly to your savings on Cooling your home.

Your doors as well as your windows should fit tightly into their frames and have gaskets that are in good condition in their frames to minimize the loss of cooled air to the outside of your home.

Wall, Ceiling and Floor Insulation

Without getting into even more technical mumbo-jumbo, you should check two things, if you don't already know them. One- check what level of insulation do you have in the walls, ceiling and floors of your home. Two- check what is the design standard for these in your area.

Hopefully, your home was built to these standards. IF not, you should consider getting quotes to upgrade your homes insulation to the newer standards. Often, you can get financial help and/or discounts from your power company for these upgrades.

There are a number of other little things that you can do that will reduce your Cooling bill to one degree or another, but these are the top three.

Some other tips that can save money are;

Close those doors

Make it a habit to keep your doors closed when you go in and out. Too many people will walk outside, leaving the door open while they go to get something from their car, yard or garage. You can actually feel the cold air rushing by your feet when a door is opened. That means that Hot air is rushing into your house. Extra Hot air that now needs to be cooled.


First of all, in the Summer, generally speaking, most people will eat lighter and fresher foods than in the Winter. These foods will require less cooking, and you should concentrate your diet on eating more fresh foods during these times of abundance.

When you do have to cook a dish, try to make something that requires less electricity and less cooking time. to prepare them. Remember, that stove of yours is hitting you from two directions when you cook. It uses a lot of electricity when cooking, and the excess heat it generates is spread into your home to be cooled.

Minimize your cooking and you minimize your elctric bill.


Because of the season, you should be wearing lighter clothes as well as less clothes. If you walk around your house in sweat shirts and PJ bottoms, you are going to feel a lot hotter, in the same temperature room than if you were wearing something simple like a pair of short pants and a t-shirt.

A person who is wrapped up in their favorite sloppy yet heavy clothes is going to feel hotter sooner that the one in shorts, and will be more prone to turning the thermostat down, unnecessarily.

Filters, Filters, Filters, and yet again, Filters

Please, please change your filters on your Heating/Air Conditioning system regularly.

You see, one of the energy consuming parts of an Air Conditioner is the inside fan that blows that nice cold air into your home.

And, letting an air filter get dirty is like slowly choking the whole system down and making it more in-efficient, over time.

The filter is there to trap the dirt and other small things that are floating around in the air in your home. If you let yours get clogged with this dirt, it is just like the person who just pulls out a dollar bill every day or so and burns it.

A dirty air filter means higher cooling costs.

So, go to your local hardware store and purchase a decent (not necessarily expensive and exotic one) air filter that you replace at least once a month. You might be surprised how much this can affect your monthly electric bill when the fan can move the air in your house around without constraint.

How to save money using your Thermostat smartly

Now let's get to how you can be smart when operating your Thermostat and save some big bucks.

As we have mentioned, all but the more modern and expensive Air Conditioners operate at a set pace and provide the same Cooled Air through the ducts regardless of the actual temperature.

If you set your thermostat to 72F, for example, it will run, continuously until the thermostat sensor detects a temperature of 72F. At which point, it will turn OFF.

Here is the way for you to save.

You do not want your Air conditioner to operate continuously. As you know, the more it runs, the more electricity it will use.

Let's look at a few scenarios;

Scenario-1:The outside temperature is 78F, and you have your thermostat set to 72F.

You Air Conditioner will operate when the inside temperature gets above 72F as mentioned,. And because the outside temperature is only at 78F, then all of those variables mentioned that make your house hotter will have less effect on the inside temperature, and your Air Conditioner will turn on less often.

Scenario-2: The outside temperature is 88F, and you have your thermostat set to 72F.

Under these, much hotter conditions, your house will absorb more of the outside heat as well as there being hotter air leaking into your house. Obviously, to offset this added heat, your Air Conditioner will turn ON more often and run longer to get rid of this added heat. And your electric usage goes up accordingly.

Scenario-3: The outside temperature is 95F, and you have your thermostat set to 72F.

This situation will often find you with an Air Conditioner that runs continuously, just because of this radical outside temperature and the fact that your Air conditioner and house are not designed to efficiently be kept cool under such extremes.

So, what do you do?

Here is a Reality Rule for many homeowners when they find that their Air Conditioners are running continuously.

First, do not set your thermostat to such a low temperature of 72F, of your AC cannot keep your house at such a low temperature.

Raise your thermostat up in two-three degree increments, until your AC actually starts to cycle On for a few minutes and OFF for a few minutes.

When your unit is cycling properly, whether you like it or not, this is the actual minimum setting you should use at such extreme outside temperature conditions. I'm sorry, but that is the reality of your AC and house design situation.

And, by operating your AC at this new temperature, your electric bill will be lower.

For the next step, now that you know the efficiency limit of your AC at this outside temperature, you can experiment and find the real limit you should use at other outside temperatures.

Nighttime temperatures versus Daytime temperatures-

So, you did everything I said and your daytime outside temperature is say, 85F and you have your thermostat set to 76F.

But, lets say your nighttime outside temperature drops to 68F, and it is too hot inside your house (with that 78F setting you used for daytime use) for you to sleep comfortably.

I recommend that about an hour before you go to bed, that you drop your thermostat setting to a more appropriate 72F for the nighttime.

You see, with the new and lower outside temperature now dropping into the sixties, your AC will run long enough to get your home to 72F and you can sleep comfortably at this new lower temperature with your AC only turning on a couple of times during the night.

Of, course, when you get up, you will need to crank that thermostat back up to the more efficient limit of 76F for the next hot day.

Doing this will save you significant money on your electric bill while giving you a more comfortable nights sleep.

Away from home temperatures-

Really, with the cost of electricity today why would anyone keep their house at cooler temperatures when they are away. This is one of the most prevalent wastes of electricity for many homeowners.

Before you go to work or anytime you are away for more than a couple of hours, you should reset your thermostat to a temperature at least 5-6 degrees hotter than normal.

Vacation Temperatures-

And , if you are going away for several days, I recommend that you set your thermostat to a temperature around 80-82F. This will allow your AC to run and pull moisture from your home while you are gone, and reduce the chance of your having Mold problems. Mold loves heat and moisture.

All of this changing of thermostat setting for so many different situations may sound too bothersome for many people, but there is one tool that costs relatively little and can do a lot of these things for you, automatically.

This tool is a good programmable Thermostat.

With many of these you can program them for multiple operating modes, such as multiple AWAY modes, DAILY modes, and HOURLY modes, along with other really neat options.

Their advertisements state that typically, if you install one of these and program it properly, you can save as much as 25%, or more on your Cooling and Heating bills.

Good Luck in your quest for better Cooling and lower Electric Bills.

Air Conditioner Preventive Maintenance for you

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.


Don Bobbitt (author) from Ruskin Florida on October 14, 2013:

Millionaire Tips- Thanks for the read and I am so glad that my article is proving to be enlightening to my fellow Hubbers.

I wrote this after I realized that a relative of mine had absolutely no idea what was really happening as they were operated their thermostat control like a pendulum willing it to change the house temperature from one extreme to another, immediately.

Thanks for the comment,


Shasta Matova from USA on October 13, 2013:

This is an enlightening article. I had read that the air conditioner is different from the heating system in that the air should not be adjusted often. I didn't really understand why, and now what you are saying about adjusting it based on the daily cycle makes a lot more sense to me. Voted up.

Don Bobbitt (author) from Ruskin Florida on June 22, 2013:

mr0veg- Thanks for the comment. And, YES there is a AC manufacturer of Air Conditioners who sells a Solar version. Lennox, manufacturers a Central home AC that has what they call Solar Assist. The AC runs on the power from it's own Solar Collector during the day, and on your regular home power at night. It doesn't have storage batteries. It does advertise that it saves over 50% off of your cooling bill, relative to a conventionally powered AC.


mr-veg from Colorado United States on June 22, 2013:

those are great tips for conserving energy as well as your bills :) Hope they invented a nice Solar powered AC :)

Mary Craig from New York on April 25, 2013:

Well done and very helpful. Many people don't realize the differences in how to control your house for air conditioning.

Voted up, useful, and interesting.

Don Bobbitt (author) from Ruskin Florida on April 24, 2013:

Fossillady- I am so glad that my explanations were helpful to you. An Air Conditioner is a complicate device if you look at it from the technical perspective, these days. But, what it does and how it does it, are pretty simple.

Thanks for the comment,


Don Bobbitt (author) from Ruskin Florida on April 24, 2013:

Janetwrite- Thanks for the comment. I really tried to with this Hub for the layman who is totally non-technical. So, I hope it helps a lot of people understand how these money consumers operate without getting into how to rebuild or repair one of the darn things yourself.

Just a simple informational Hub.


Kathi Mirto from Fennville on April 24, 2013:

Written very well for the layman to understand. I learned the basics of how the cooling boxes 1 and 2 function and I'm glad to know this! I pretty much do the same things you suggested with keeping the elect bill down, so I feel pretty good about it! Thanks Don

Don Bobbitt (author) from Ruskin Florida on April 23, 2013:

conradofontanilla- Such a good question. Your Oxygen level concerns when in a conventionally constructed house are not relevant. So many people think they have a well built home, and thus one tat is "air-tight". But, the reality is that a typical house is a literal sieve of cracks and leaks, that the oxygen loss is easily offset by just a few healthy plants. But, a submarine or spacecraft are totally different things, in that their designs are inherently sealed containers. Such human containers require some very complex air processing systems.

Thanks for the comment,


Janet Giessl from Georgia country on April 23, 2013:

A well-written, comprehensive, informative and useful hub about air conditioner. I could learn a lot from it as my experience with air conditioners is relatively low.

Don Bobbitt (author) from Ruskin Florida on April 23, 2013:

ShiningIrisheyes- Great point on the climate differences in our colder northern climates. I do not envy you your winter electric heating bills. Whew!

Thanks for the response,


conradofontanilla from Philippines on April 23, 2013:


Enlightening piece. I wonder if the airconditioning system sucks in new air from the outside thus sucks in new oxygen, molecular oxygen. Air that is kept circulating will get exhausted of molecular oxygen owing to use by the room occupants, I presume.

I worry that circulating air in an airconditioning system will eventually fill with carbon dioxide exhaled by occupants and molecular oxygen becomes less and less. I get harder in breathing in an airconditioned bus after two hours inside it, with all seats taken. Is there a difference between an airconditioned bus and an airconditioned living room with regard to new and fresh air thus molecular oxygen?

Pat Materna from Memphis, Tennessee, USA on April 23, 2013:

Bob ... good article .. useful stuff to know! Voted up and useful

Shining Irish Eyes from Upstate, New York on April 23, 2013:

Well - I commend you for a thorough and easy explanation. I also agree with the helpful hints. We live in Upstate NY. As your article states, our winters are brutally cold. One thing some my be surprised about - how humid our summers are. Closing the blinds, curtains or drapes as well as providing a secure seal at windows, doors and other openings makes a huge difference. Not only physically but through the energy bill as well.

Don Bobbitt (author) from Ruskin Florida on April 22, 2013:

Thanks for the response, FlourishAnyway. I hope this Hub will be useful to a lot of people.


FlourishAnyway from USA on April 22, 2013:

Good explanations and recommendations, especially on temperature settings for time away.

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