39 super tips for saving money on cooling and air conditioning costs

In the typical home, air conditioning uses more electricity than anything else—16% of total electricity used.  In warmer regions AC can be 60-70% of your summer electric bill, according to Austin Energy.  This is where the savings are folks, not in worrying that you left your cell phone charger plugged in too long.

The easiest way to save is to run the AC less often, and to dial the temperature up a degree or two when you do run it.  My tips below show you how to be comfortable at warmer temperatures.  I use these tips myself, and as a result I save hundreds of dollars every summer.  I could take a trip to Las Vegas every year from what I save by not using AC.  Even if you're determined to not use your AC any less, we'll cover ways to keep the heat out of your home, and more efficient air conditioners, which can still save you money.

Central AC is simply an energy hog.  A window unit AC uses 500 to 1440 watts, while a 2.5-ton central system uses about 3500 watts. That's a lot of power.  A floor fan uses only 100 watts on the highest speed, and ceiling fans use only 15 to 90 watts depending on speed and size.

1. Raise the temperature

2. Install ceiling fans if you don't have them.

Is raising the thermostat a degree or two really gonna kill ya?  I don't turn on my AC unless it's more than 96 degrees outside, and then only if my computer is running.  Each degree below 78°F will increase your energy use by 3-4%.  Follow the other ideas in this section, and you'll feel cooler at warmer temperatures.  Remember, only losers set their AC below 80. Fans can make you feel 3 to 8 degrees cooler, allowing you to dial your AC to a higher temperature and still feel just as cool. (NY Times)  Put the wind-chill factor to work for you!  And ceiling fans are cheaper than you might expect: they start out around $40 at your local home improvement store, and usually cost less than a penny an hour to run. (A typical 36" / 48" / 52" ceiling fan uses about 55 / 75 / 90 watts of electricity respectively at the top speed.) Central AC costs seventy times more to run than a fan.

Most people are even able to install the fans themselves using the instructions provided.  Don't underestimate the importance of ceiling fans!

3. Make sure your ceiling fan is spinning the right way.

Make sure your fan is blowing DOWN, to send air past your body, removing the hot air that surrounds your body. If your fan is blowing up, it won't do any good.  In fact, it's worse than no fan, because it moves the warm air at the ceiling back down towards the living area.

(It's true that a fan that blows down also pushes the warmer air down from the ceiling into the living area, but it's blowing even warmer air away from your body, so the overall effect is to cool you down.)

Almost all fans have a switch to change the fan direction.  It's an up/down or left/right switch on the side of the fan (between the light and the fan blades), and it's usually unlabeled.  Make sure the fan is off (not spinning) before you flip the switch or you can damage the motor.  Once you've turned the fan off, it's fine to physically stop the blades with your hand, just be gentle so you don't bend the blades, otherwise the fan will wobble when you turn it back on.  With the blades stopped, flip the direction (summer/winter) switch, then turn the fan back on.

So how do you know which direction is up and which is down? For most fans, when you're standing under the fan looking up, counter-clockwise blows down and clockwise blows up.  Check by standing under the fan when it's on full-speed.  If you can feel the wind hitting you hard, then it's blowing down. To verify, stop the fan, change the direction switch, then turn the fan on full-blast again and compare the difference.

4. Use a Bed Fan

5. Use a "Chillow" pillow

Why pay to cool the whole house while you're sleeping when you really need to cool only yourself?  The Bed Fan solves that problem, running a gentle breeze under the sheets to keep you cool, so you don't have to run expensive AC (or so you can dial up the temperature, which still saves money).  Why didn't someone think of this before? This could be also great for people who experience night sweats or hot flashes. And you won't have to run an expensive AC all night long. Order for $99.95.

The Chillow is a water-filled pillow that keeps your head cool while you sleep. You can either sleep directly on it or put it inside a pillow case. I bought one as soon as it came out and it really works. Order for $30.

6. Use cold packs
7. Wear a wrung-out shirt
Put these pads in the fridge or freezer, and then wear them or sit on them (or use as pillows when you're sleeping).  The cost to chill them in the fridge is a fraction of what you'll save by being able to dial your thermostat up a degree or two.  Check out the Ice Bandana ($9) and the ColPack ($20+).  Remember, it's cheaper to cool yourself than the whole house.
You'll probably be surprised at how well this works.  Afterwards you might wonder why you didn't try it sooner.  It works even better if you combine it with a fan.

8. Run around naked

9. Rinse off in the shower

Okay, you probably don't want to run around naked, but wearing lighter clothes will make you cooler.  Why wear long sleeves and long pants inside the house?  Wear a t-shirt and shorts and then you can dial up the thermostat a degree or two.  But if you do go naked then you'll also save money on laundry.

A quick, cool shower can keep you cool for quite a while afterward.  And the water cost is trivial compared to the electric cost.

 

The Air Conditioner itself

10. Use an AC timer or smart thermostat.

For central AC, your thermostat might already have a timer built-in.  If not, you can replace your thermostat with a programmable one.

For window unit AC's, many modern units have a timer built in.  If not, you can use a simple plug-in timer if your AC has a mechanical On/Off switch (i.e., you physically move it into a different position when you turn the AC on).  But plug-in timers usually don't work if the On/Off switch is electronic (i.e., you push a soft button on a panel to turn the AC on or off).

Set your timer or thermostat to turn off about the time you leave for the day, and to turn back on a half hour before you get home. Contrary to popular belief, this does NOT use more electricity than having the AC constantly maintain a cool temperature; it uses less.

You can get programmable thermostats and plug-in timers from your local home improvement store. Programmable thermostats come with instructions, but it's a quick job for an electrician if you're not comfortable doing the installation yourself. Plug-in timers for window units start out at $5, and there are more expensive models with more features.

It's a myth that it takes less energy to run the AC all day, rather than leaving it off and turning it on when you get home.  Running the AC all day when you're away definitely uses more energy, no question.

The reason is that with the AC constantly running, it's constantly cooling your home, making it a heat magnet.  Heat goes to where it's not, so when your house is cooler, more heat will try to enter.  So more heat gets into your house, and the AC has to remove that heat, over and over again.

But if you leave the AC off, then the house will heat up during the day and then stop heating up. It's already hot so it's no longer a heat magnet.  When you get home and turn on the AC, the AC has less total heat to remove than if it had been running all day.

Yes, I've tested this, of course.  In my test, running the AC all day used 317% as much electricity as waiting until after work to turn it on.  It was a pretty crude test and I won't be surprised if the typical penalty is actually much lower, but the point is, there's definitely a penalty by running the AC all day.  I hope readers will run their own tests and let me know the results.

Since this topic garners a lot of interest, I have a special page all about leave the AC on when you leave home or not?

11. Clean the filter

12. Replace your air conditioner

Clean or replace your AC filter every month.  A dirty filter makes your AC work harder, which uses more electricity.  Your home improvement store sells permanent filters which you can easily rinse off so you don't have to replace the filter each month.

Before replacing your existing central AC, consider the alternatives to a traditional AC listed in the special section below.  They include room-by-room systems (so you don't have to pay to cool the whole house if you're using only part of it), whole-house fans, and geothermal systems.

If you're determined to keep using a traditional AC, then use an efficient one.  Energy Star models use 15% less energy than other new models, and up to 30% less than models ten years old. (EPA)

Whatever system you get, look at the energy ratings (SEER for central systems and the EER rating for window units). The higher, the better. SEER 13 are 30% more efficient than SEER 10. (EPA) 

As of 2006, AC's must have a SEER of at least 13, although they go as high as 19. Both the inside and outside units should be a similar SEER for best efficiency. (See more about SEER from AC Doctor.)

Whatever you get, make sure your AC is sized properly. (See next item.)

13. Don't oversize when buying a new AC

14. Use the Energy Saver on window units

An AC that's too big is inefficient and wastes money!  You want your AC to run at least ten minutes when it kicks in. (DOE, HomeEnergy)  Oversized AC's cool the house down too quickly and then cut off before they've reached their most efficient running level.  A properly-sized system that runs longer saves money over an oversized system that runs for shorter periods of time.

A properly-sized AC will run 15-30 minutes per hour when the outside temperature is 85-90°F, and almost constantly when the outside temp is above 95°. (source)  Here's a good story about improper sizing.

It's also widely held that oversized AC's also fail to remove enough moisture from the air, but at least one study says otherwise.

Here's an AC sizing calculator for window units.  For an HVAC system, it pays to have an energy auditor do a Manual J calculation to figure the cooling load, and then a Manual S calculation to figure the system size.  (Here's ExpressHVAC's rough estimate calculator and Mr. HVAC's more elaborate calculator, but I wouldn't rely on them for a purchase decision.  I would also use Manual S over the rule of thumb of one ton of AC per 12,000 BTUs per hour.)

Normally, when the desired room temperature is reached, the compressor on the window unit shuts off but the fan keeps going—which is wasteful.  But many modern window units have an Energy Saver button that turns the fan off when the compressor shuts off.

Of course, I got a window unit AC that has just such a button.  I measured the unit with my Kill-A-Watt meter and found that the fan alone uses 84 watts.  If I kept the unit on 24/7, and the compressor ran 50% of the time, that would be 84 watts x 12 hours/day x 30.5 days/mo. = 30,744 wH, or 30.7 kWh.  But thanks to the Energy Saver switch, we're not paying to run the fan gratuitously.  (Though of course, in Mr. Electricity's household, we don't run the AC 24/7 in the first place.)

 

 

The Condensor

15. Cool your condenser or window unit

16. Shade your condenser or window unit

An AC Mister makes your AC run more efficiently by cooling the condenser with water vapor as it runs.   The drier the environment, the better the performance will be.  Reviews on Amazon are mixed, some folks raving about the savings, others worried about corrosion from hard water.  Me, I'd try it if we had a central system, but we use window units so we don't have to cool the whole house. (starting at $50 from Amazon)

Condensors in the shade use up to 10% less electricity than those in direct sunlight.

17. Don't block the condenser unit

18. Clean the condenser/evaporator coils at the begininng of each season

Tall grass and other debris on or around the condensor can restrict air flow and use more electricity.

You can wash the fin coils on the outside with a garden hose. Unless you know what you're doing, have the coils on the inside serviced by an AC specialist.

 

Alternatives to HVAC central air conditioning

19. Alternative #1: Window Units

20. Alternative #2: Mini Split System

Central AC is wasteful if you don't use your whole house all the time.  It's cheaper to cool just part of your house rather than the whole thing.  Window unit AC's let you cool just the rooms you're using, and there are no energy losses through a duct system.

Don't think you can achieve the same thing by closing registers in unused rooms.  Doing so promotes duct leakage which actually winds up costing you more. (Lawrence Berkeley Labs)

Mini-split systems are neat. You have an outside condenser, like with a central system, and that runs directly to a cooling vent in each room -- without any ductwork. Think of it as a window-unit AC that you mount on the wall instead of the window, and which is a lot smaller since the actual cooling apparatus is located outside.

These save a lot of energy compared to central systems because you cool only the rooms you need to cool rather than the whole house, and because there are no energy losses through ductwork in a hot attic.

21. Alternative #3: Evaporative cooling

22. Alternative #4: Whole-House Fan

An evaporative cooler works by blowing water-cooled air.  It can be a free-standing unit in your room, or a window-mounted unit, or a whole-house unit.  Evaporative coolers use a lot less electricity than an regular air conditioner, and they work well in dry climates (like Nevada, West Texas, etc.)—but they don't work in very humid climates at all.  (Here's a U.S. map and world map showing where evaporative coolers work well and where they don't.)  These coolers use only about 3 to 15 gallons of water a day, too. (source)  Portable floor-standing units start at around $100.

A whole-house fan is a large fan that mounts in your ceiling. It draws in fresh air from open doors or windows into the attic, where it's then pushed out through attic vents.  This creates a cool breeze through your house, and at the same time gets the super-hot air out of your attic.

Personally, I bought an AirKing from Amazon ($136) but haven't yet installed it.  I'll report back here once I have.

Read more about whole-house fans on Wikipedia.

23. Alternative #5: Geothermal systems

Geothermal systems use 30-60% less energy than typical HVAC systems, run quieter, and require less maintenance.  They can also heat your water, too, and in the summer it's free, since the water is heated with heat that's already been extracted from the house to keep it cool.

A geo system is a loop of piping under the ground that circulates water. The heat is extracted from your home, run through the pipes, and the earth absorbs the heat from the water.  Basically, the heat is taken out of your home and put into the earth. This isn't so different from a traditional AC system, which extracts the heat from your home and puts it into the air outside your home.  A geo system is just a lot more efficient and cheaper to run.  (See the EPA's great video which shows how geothermal systems work.)

Geothermal heat pumps meet the EPA's Energy Star guidelines if they're labeled at least COP 2.8 for heating and EER 13 or for cooling.

U.S. homeowners can get a whopping 30% tax credit on geothermal systems through 2016.

In 2006 a geo system cost about $2500 per ton of capacity to intall. A 3-ton geo system at $7500 compares with $4000 for a traditional system, for a $3500 up-front premium for the geo system. (EPAA geo system could save in the neighborhood of $700/yr., paying for itself in less than six years, not even counting the lower maintenance costs.  Also, many city and state governments offer rebates and other incentives for installing geo systems, making it an even more attractive deal.  On the other hand, depending on the geology of your area and the availability of local contractors, a geo system could cost a lot more than $2500/ton to install.

I had a hard time finding really good figures to base my calculations on, but the above should be in the ballpark.  For AC, I'm figuring 50% savings over a 3-ton (4200-watt) AC system running 12 hours a day for five months.  There's also savings on heat, even if the old heat source was gas or oil, but heating savings are harder to figure, so I'm estimating that they'll be a bit below the savings on cooling. (Here's a cost comparison of different systems from GeoExchange.org, PDF.)

 

 

 

Attic, Roof, and Exterior

24. Insulate the attic

25. Install a radiant barrier

Poorly insulated attics can lose up to 40% of a house's cool air. The average home built in 1985-90 has R-11 to R-15 insulation but needs up to R-49. See the DOE's map for how much insulation you need depending on what part of the U.S. you live.

Baltimore Gas & Electric says that increasing the level of insulation from 2-3 inches (R5) to 8 -14 inches (R30) can save $95 to $145 per year for every 1,200 square feet of ceiling area.

Cellulose is better than fiberglass for blown-in attic insulation.

A layer of aluminum foil-type material or special paint across the underside of the roof in your attic blocks heat radiated into the roof, and reduces energy use by 3-8%.

Besides decreasing the amount of attic heat that radiates into the living space, it might reduce the heat enough that you could consider turning the attic space itself into a living space.

26. Test your ducts for leaks

27. Paint the exterior with a light color

Austin Energy tested thousands of home duct systems and found that the average home loses 27% of its heating or cooling from leaky ducts. (2006)  And over 86% of homes had ducts which lost more than 10%. (June 2009)  Leaking ducts and insufficient insulation meant that the average home used 162 kWh/mo. extra electricity per month (July 2009), or 18% more than normal. This is an extra $233 a year at average electrical rates.

See if your local utility will perform a free or rebated duct test, and if not, have an AC proffesional do it. The money you save by repairing leaks should easily pay for repair.

Note that those in hot climates like the Southwest U.S. should use mastic sealant because regular duct tape will dry out.

The next time you have your home painted, use a light color, which will reflect more heat than dark colors.


You might think that by going with a light color you lose the benefit of the extra heat for winter months, and so the savings cancel out.  But in reality, you save much more in summer than you lose in winter.  The only exception is in frigid areas where you rarely use air conditioning, and use heat much more than normal.  See the section below on white/black roofs for more on this.

28. Install a metal roof

29. Install a white roof

Metal roofs reflect much more heat away from your home than do regular asphalt shingle roofs.  If you don't like the way metal panels look, there are newer metal shingles that look like attractive wood shingles.  Another benefit is that metal roofs are permanent so you never have to replace your roof again (unlike asphalt shingles, which must be replaced every 15 years or so and wind up in the landfill).  I have a home today that still has the original metal roof installed in 1951, long before I was even born.

When you replace your roof, metal is best.  If you don't go with metal, then at least go with white.  A white roof typically saves 10%, and up to 20% on cooling costs. (PhysOrg, YouTube)

You might wonder whether your savings with a white roof in summer are canceled by your losses in winter, when your roof won't absorb as much heat.  The answer is that while you do miss out on free winter heat, the savings in summer are greater than the winter penalty, in all but the most frigid areas.  This map from the Dept. of Energy shows a net energy savings from white roofs in even the nothernmost U.S. states, even after considering the winter penalty.  A roofer explains in more detail why the white-roof savings in summer outweigh the loss of heat in winter.

The U.S. Secretary of Energy has said that if the world’s 100 largest and hottest cities switched to white roofs and light-colored cement pavement for roads, it would be the equivalent of taking all the world’s automobiles off the road for 11 years. (YouTube)

(And yes, I know all about the special tiles that magically change to white in summer and black in winter, but until they're commercially available, they don't do us any good.)
30. Plant shade trees
Well-positioned shade trees can reduce indoor temperatures by up to 20 degrees and energy use by up to 40%.

31. Install an attic fan?


While a whole-house fan sucks air through your whole house (see "Alternatives", above), an attic fan sucks air only through the attic.  Attic fans aren't usually called for because they don't give a lot of bang for the buck.  First of all, if your attic is properly insulated, then the effect of the fan won't be that great.  (And if your attic isn't properly insulated, getting insulation put in is more important than installing a fan.)

Second, if you normally use air conditioning, then the fan could actually draw cool air from the living space into the attic, if your light fixtures, ducts, and attic access aren't well-sealed.  Third, in rare cases attic fans could actually backdraft combustible gases through the house.  And finally, the electrical cost of running the fan will likely exceed the energy savings from cooling.  You could get a solar fan, but in that case the payback period would likely be a long time.

So if your attic is already properly insulated, and if you don't use AC or your attic is very well-sealed from the living space, and if you don't have gas appliances or aren't worried about combustible gas, and if you use a solar-powered fan so you're not paying to run it, then an attic fan might help, a little.

Austin Energy says reducing the attic temperature by 10 degrees or more saves up to 10% on AC costs.  They didn't disclose how much insulation the attic had though. I'll try to run my own test if I can ever find the time....

 

Doors and Windows

32. Make sure your doors and windows are well sealed.

33. Use drapes or blinds to block sunlight

You'll pay a lot more to cool your home when the cold air easily escapes. Do-it-yourself weather stripping for doors and caulk for windows is easy to install, and cheap. Also make sure to caulk around the holes where pipes go into the wall under sinks.

Also, close the damper to the fireplace when you're not using it -- otherwise, cool air will escape through the damper.

Keep direct sunlight out. Direct sunlight can raise the temperature of a room by 10-20 degrees. The less heat gets into your home, the less you have to pay to remove it. Drapes block sunlight and heat better than blinds.

34. Put solar screens on the windows

35. Install reflective film on windows

Solar screening is a special mesh that reflects much more sunlight than regular screening. It's available at home improvement stores, and can block 60-70% of the heat from sunlight. Get screens that don't block too much light, because if your building gets too dark and you wind up using more lighting inside as a result (which generates heat) then you've defeated the purpose of the screens.

Windows let lots of heat into your home, because they're not nearly as insulated as your walls (if at all).  Combat that heat infiltration with reflective film, which reflects 40-60% of the sun's heat from your windows, and can do so without blocking the light too, so you can still have nice, bright rooms.  Film costs about $3-7.50 per square foot installed, or do-it-your-selfers can get the material from a home improvement store for about $1-2 a square foot.  The payback period is 3 to 5 years (or maybe less, if the cost of electricity continues to rise).  It's critical to use film that blocks very little light, otherwise you'll run more lighting inside which will heat up the building and defeat the point. (more from ChiefEngineer.org)

36. Use storm windows & doors


If you're ambitious, install storm windows and doors. They can reduce the amount of cooling or heating lost through single pane glass by 50%.


 

Reducing Heat

37. Reduce heat from lighting

38. Reduce heat from cooking

Lights create a lot of heat which your AC system has to remove. Replace your lights with compact fluorescent (CFL) bulbs, which use 75% less energy and create 70-90% less heat at the same time. Regular lights give off 10% light and 90% heat, while CFL's give off 90% light and 10% heat.

In winter months when you're heating your home, there's no penalty for the extra heat created by your lighting.  The extra heat created by inefficient lights means that you pay less to heat your home.  (In theory there's a difference if electricity costs much more or much less than heating fuel in your area, but it's almost never worth worrying about.)  But while there's no penalty for using inefficient lights in winter, there's no savings either.  So with inefficient lights you pay a heating penalty in summer, and break even in winter.  And you pay a lighting penalty for inefficient lights year-round.  So yes, go with more efficient CFL's or LED's.

Any heat you create from cooking has to be removed by your AC. Reduce cooking heat by using a microwave oven. (Microwaves are cheaper to operate than gas or electric ovens anyway.) Move your gas or electric oven to be along an exterior wall, if possible.

 

Miscellaneous

39. Use software to model your building

Trivia: The EER is the number of BTU's divided by the number of watts. BTU's are British Thermal Units, and refer to how much heat an AC can remove from a room in an hour. A 7000 BTU window unit that uses 655 watts has an EER of 7000 / 655 = 10.7.  Central AC systems are so large they're measured in tons instead of BTU's.  One ton = 12,000 BTU's.

For those who want good data, you can get software to calculate the heat gain and heat loss in your home or business.


The Fan Switch. Here's how the fan switch on a central AC system works: If the AC is off, then turning the fan on will simply recirculate the inside air without cooling it. (It draws in through the intake and blows out through the ceiling vents as it normally does.) There's not much advantage to this, because it doesn't make the house any cooler, but it can help keep the air "fresh" since it's being drawn through the filter and it's being moved around a lot.

When the AC is on, the air's already being circulated, so in that case there's no difference whether the fan switch is on or off.

The fan by itself doesn't use much energy. It's the cooling part of the AC system that uses most of the power.

How ceiling fans cool you


Fans don't make the air cooler! They work by blowing away the envelope of warm air that surrounds your body.

As a living creature, you generate heat. A lot of it. As that heat slowly radiates away from your body, it creates a pocket of hot air that surrounds you. It's like you're being insulated by an invisible bubble of heat. What fans do is to push that hot surrounding air out of the way.

This is why blowing on hot food cools it off. It's not that your breath is especially cool, it's that you're blowing the heat off the food.

If you're sweating at all then the fan also cools you by speeding up the evaporation.

So now that you know that fans don't make the air cooler, you can see that there's no advantage to leaving the fan on when you leave the room. Fans don't lower the temperature in the room at all.

By the way, a typical 36" / 48" / 52" ceiling fan uses about 55 / 75 / 90 watts of electricity respectively (less on slower speeds).