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How Not to use your Air Conditioning

Happy July 18th. It sure is hot these days, isn’t it?

Statistically speaking, a good portion of the continental US and Canada has its hottest average day of the year right around now. So I thought it was a good time to share some thoughts on the modern household’s biggest energy consumer in July – the Air Conditioner.

See, normally I’d assume that we’re all adults and we’re able to decide for ourselves how to run our own appliances. But after being on my current summer vacation for over three weeks and visiting a large number of family and friends throughout the not-overly-hot Great Lakes region, I’ve noticed that most people leave their goddamned air conditioners running 24 hours a day, whether it is warm or cool outside, with their houses at a stupidly low temperature. Yes folks, it has become obvious that America and Canada both need a lesson from Mr. Money Mustache on how to use their Air Conditioners.

I recently measured the power consumption of the central A/C system in my own house. Mine is a “3-ton” (36,000 BTU/hr) system which dates back to about 1998, when my house was built. At the time, it was considered fairly efficient with a seasonal energy efficiency rating (SEER) of 10. Newer units, thanks to EPA rules, are now much better with ratings of 14 and higher – changes the SEER rating translate almost directly into similar percentage decreases in your cooling costs. When in full operation, my system uses 3,000 Watts (3kW) of electricity, about 500 of which is my furnace blower pumping the cool air around the house (and adding its 500 watts of heat back into the cool air stream, by the way).

For those without electrical engineering backgrounds, 3,000 watts is an Absolute Shitload of electricity. It’s enough to run 230 modern light bulbs simultaneously, and it’s equal to having about 15 monster-legged tour-de-France-level cyclists hooked up pumping at race level on bike generators continuously in your basement.

At the national average price for electricity of 12 cents/kWh, my air conditioning system burns 36 cents per hour, or $86 per month if used for 8 hours per day. With a three-month cooling season, this would compound to SEVERAL THOUSAND dollars of wasted electricity every ten years. Yet my TOTAL average electric bill in summer, despite an average daily high temperature of almost 90 degrees in Colorado, is really only about $35. How could this be?

The answer of course is that I have just cut out the waste, without sacrificing any real happiness or comfort.

Here’s how comfort works. Your body generates heat just by being alive. It needs to maintain its internal temperature at around 98 degrees F, and it depends on the skin surface temperature being lower than this to dump extra heat into the surrounding air. Producing sweat helps you cool the body faster, since the sweat sucks up heat as it evaporates. Humid air cannot evaporate your sweat as quickly, which is why it feels hotter. All basic elementary school science, right? This is why the Southeastern United States is a sucky place to be in summer even at 85 degrees F, while the desert states can feel quite comfy and invigorating at that temperature.

Finally, your body becomes more efficient at cooling itself the longer it spends at higher temperatures and humidities. Every summer as I drive from Colorado down into Nebraska and beyond, I break out into a great sweat and need to crank the car A/C. Even at midnight when the temperature drops into the sixties, I still can’t stand the humidity and need to continue the air conditioning. But within two days, I am comfortable with the higher humidity and I enjoy a regular Eastern summer with no difficulty. As July progresses and things get hotter, I am usually visiting a portion of my family with no A/C, so my body continues to adapt. There are a few days when the temperature is so high that I get uncomfortable, but then I spray myself with the garden hose and drink a gallon of water with ice cubes and all is well.

I also take advantage of the natural cycle of the environment. In the US Northeast and Canada, and even more in the Western desert areas, the temperature usually drops at night. So non-A/C users take advantage of this fact to open all their windows, and use large fans (100 watts) to exhaust heat and draw in cool air to chill the entire interior contents of their homes. A 100 watt fan blowing outwards from your highest window is pulling in night air from all other windows that is 10+ degrees cooler than your house. By sucking in thousands of cubic feet of cool air per minute, this fan is doing almost as much cooling as the 3,000 watt air conditioning unit that does the same job during the day time. The Naturally Cool crowd also makes a point of enjoying more outdoor food cooking and clothes drying on hot days, to further reduce indoor heat sources.

This is to be contrasted with the behavior of Air Conditioning addicts, who set their thermostats to a silly temperature below 80 and let that baby run, night or day. They might turn it off at night, but forget to open the windows, so they miss out on the free night-time cooling. I remember staying over at one friend’s house in June and heading out for a midnight errand. It was so cool outside that I needed a sweater. Yet his air conditioner was still running, pumping out the remaining heat from the 90-degree sunny day that had just passed. Meanwhile his body was not bothering adapt to summertime heat and humidity, because his house was always refrigerator-like inside. All of this is completely unnecessary!

The Mustachian Way is to think of Air Conditioning as a pleasant luxury to be used when all other efforts fail. Much like a car. It should be an exciting moment in your household, when every one is drinking their gallon-sized containers of icewater, wearing comfortable and summery outfits of bare feet and tanktops, and the ceiling fan is running, when you proclaim, “God Dammit it is hot today!! Let’s turn on the AIR CONDITIONING!! YEAH!!!!”

Then you run it for an hour or two, and the sun goes behind a tree, and you shut it back off again. And you open the windows that night and run the fan and go on with your lives.

If this sounds like too much hassle to you, grow some Frugality Muscles, punch yourself in the face, and try again. This is my Earth you are messing with, and your own Money Mustache you are burning off in the boiler of your local Coal-fired power plant.

Stay Cool!
love,
Mr. Money Mustache.

  • Kenneth August 19, 2015, 12:22 am

    Hm , After reading the blog ( and I agree with those good words ) and all the comments I can only say
    the problem is extremely big here in china.
    I live in shenzhen and almost all places and everybody use AC .
    My wife is working whole day in AC envrionment and this have actually change her body to no longer be able
    to handle the natural heat.
    Result — Always want AC to run at full power.
    This is a big problem both by cost in money but also for the envrionment .
    Yes If all those people they could CUT off their AC then we could save million of tons CO2.
    It’s true. How many AC do you think is in a city like shenzhen ? close to 20 mill people ….
    ansver – about 6 AC for each person. plus all the big systems in shopping malls ect.
    Cut it all off then the electricity use of the city is reducen to one third.
    It is the same problem in all modern cities.
    Yes we have a very hot climate.
    BUT one single Fan at 35 Watt running in the correct window can send a nice cool breese into the apartment.
    Ceiling mounted fans are both cheap and use less electricity and cool at an ok ratio.
    even single rooms here at 10 m2 have AC at more than 2700W its totally overkill.

    Our AC was run so much ( I didnt stop her using , nope I just waited until no more AC , ha ha )
    That it broke down and now is completely damaged.
    ( shure I do “”not know “” how to fix it , ha ha )
    Problem solved itself.
    Now running a 35 watt air fan ( compared to a 3500 watt AC ) I both save money on electricity and
    more important I produce much lesser CO2.
    And the final most important : Climate inside the apartment is now actually much better
    and for me the warm hot climate is’nt any problem ( thats why I moved here )

    If all people could shut down all those AC that constantly running them we could save extreme amount of CO2.

    Go Green both for climate and your body.

    Great blog and I wish u sucess in future :O)

    Reply
  • Ishabaka August 28, 2015, 3:14 pm

    I’m a Canadian who’s moved to northeast Florida, and need my A/C in summer (and heat in the winter sometimes, as it has gotten as low as 13 degrees F here). That said, I have managed to reduce my costs a LOT. First – insulation – cheap, and lasts virtually forever. I sealed all my outlet boxes with Styrofoam gaskets, sealed all ceiling penetrations with expanding foam, and put an extra layer of 6″ fiberglass in the attic. Less than $500.

    Next – when my old, inefficient unit wore out, I spent the money on a high efficiency, dual speed unit – saves a TON of electricity. This cost a few thousand more than a low efficiency system, but over the around 20 year lifespan, I should recoup the cost, and more. A lot of people don’t understand, the A/C doesn’t just cool the air – it dehumidifies it, which is just as important as cooling, especially here, where the humidity is 80 – 90% a good part of the year.

    Next, I got a smoke pencil (really, an electric glycerine vapor generator), and sealed all the leaks in my plenums I could find with caulk and aluminum foil tape (NEVER use duct tape – it is NOT for ducts! It’s adhesive becomes hard and brittle with thermal cycling, and the tape will fall off in a few years). You would be amazed how many leaks a “professionally installed” system has – it’s estimated that the air leaks in an average North American house amout to havin a three foot by three foot window wide open all year round. Less than $200, and a smoke pencil kit (about $80) could be shared with friends and neighbors.

    Reply
  • Jacques September 8, 2015, 1:03 pm

    I took a trip to Buenos Aires in December 2014 and joined a tour group for half my trip. I’m South African and my two roommates were from the States and the UK respectively. We usually got up early wherever we were staying, went out for the day and got back in the evenings. Both of them insisted on leaving the A/C (or fan, if that was all that was available) on during the time that we’re out, so that the rooms werecool when we get back. (It was quite hot in BA in Dec, even for me as a Saffa – but not unbearable). We argued about it in a respectful manner, even though I wanted to slap them straight. In the end, they saw absolutely nothing wrong with it. Arguing that big industries screw up the planet so much, that their actions won’t make the least bit of difference. I just naturally assumed common sense was, well, a bit more common than that. Seems not.

    Keep up the legendary work Triple M – I enjoy reading and implementing your strategies.

    Cheers

    P.S. I always pretended to forget something, went back and turned everything off. Including the lights, which they usually left on as well. ;)

    Reply
  • Matt K September 18, 2015, 1:41 pm

    I can’t believe nobody called you on the cyclist equivalent calculation :D. A TDF cyclist at race pace is putting out more like 400 watts so it would only be 7.5 of them cranking for a 3000 watt unit! Someone like Sagan sprinting for the line (after 160 miles) is putting out upwards of a 1000 watts for a burst of time.

    Reply
  • Suhaila September 22, 2015, 11:57 pm

    My issue with opening windows at night is safety. We live in an apartment on a busy street on the first in the LA area. And we don’t have window bars which I’m not fond of anyway. I have only two AC window units which I don’t use at all because during the day it’s fine with just fans & open windows and at night our bedroom is not one of those rooms that has the wall unit in anyway. Not fun. But that’s our bad because we spent 7 years out here spending our money like idiots. Only started to really change in March of 2015 slashing eating out and ditching soda and getting serious about having a budget. Still screwing up but no where near where we once were!

    It’s also just super hot this summer compared to last(before that we had central air and abused it). We had our highest bill since we moved into this none central air apartment and our highest bill has been 107 for a two month period which had a lot of record heat days so I think we’re doing okay. It’s usually around $75-$90 for a two month period.

    I used to live in Florida and may return there someday and you need AC almost year round. But if I went back I’d be buying a house and would look into getting room specific wall mounts (Mitsubishi) that only cool that one room. Only really need one or two rooms going at a time (daytime living room, night time bedrooms). At least that’s my plan to avoid $150/mo electric bills if I go back! They were usually around $80 unless it was spring/summer time and would spike high.

    Reply
  • Stephanie March 20, 2016, 9:58 pm

    I do have to say that I used to live in Charleston, SC and I did this all the time. I only ran the AC in July or August (historically the hottest months) I survived. I remember my Dad making a game out of who would cave in to admitting they were hot in the summertime first. We had fans and opened windows at night. It was just how we lived. People used to come into my house and ask me why the windows were all curtained up. I told them I was blocking the heat out. If you want light go outside. Whiners all of them. I mean it’s not like I was burning candles or sitting in the dark. I had a light on so I could see, but light would still get in the house. We didn’t have fancy blackout curtains. Now I live in MN and I open the curtains in the daytime in the winter to let the sun heat the house. It’s amazing that I ever thought 40 degrees was cold. Now when it’s 40 I’m outside playing in a tree shirt. It’s all about what you can adjust to really. And in MN our windows stay open in the summer. It’s not like it’s hot…ever.

    Reply
  • Sara May 10, 2016, 12:36 pm

    A couple years ago, my husband and I were living in a barn loft that had been converted into an apartment in Logan, Utah. There was no AC, and being above four other apartments that also had no AC meant our apartment was boiling all night long and worse in the day.

    We were the only apartment lucky enough to have a swamp cooler, probably because some previous tenant had left it behind and it just got added to the management’s maintenance without much question. We would run it as a fan all night long, pumping cool air in through the back window and pushing hot air out the front. Then as interior temperatures climbed toward 80 during the day we would turn on the cold full blast all day long to combat the heat rising from below and the sun beating down on the metal roof above with no insulation.

    Our electric bills were atrocious there. $90 a month minimum for barely heating/cooling 320 square feet, plus a tiny fridge and 5 light bulbs and an oven. It pays to pick a place with insulation… or be on the ground floor.

    Reply
  • Brent August 10, 2016, 9:31 pm

    Engineers out there? I need a fan like the below, except with accurate temperature and humidity sensors, and the ability to control the incoming and outgoing fans separately. Anyone know of such a product???

    https://www.amazon.com/gp/product/B008Y9U266/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=A3V9HZN3IY3FMM

    Reply
  • Kirk October 10, 2016, 8:50 am

    We are retired and living near Windsor, Ontario, opposite Detroit, Mi for the past 4 years. I do try to use the natural night time cooling cycle with fans but this last summer was an exception. If the temperature and HUMIDITY is low then I will open the windows. There is little to no point in lowing the humidity in your home with your ac and raising it by opening the windows. The primary cost and purpose of ac is to lower the HUMIDITY as it is what costs you money when you operate your ac.

    Our system is 26 year old SEER 10 2 ton single stage. We have a modest raised ranch with 1000 sq ft up and 900 sq ft down stairs with the lower level being about 3 ft in the ground. I was looking to replace this with a two stage 3 ton unit but have decided that a 2 1/2 ton Seer 16 should more than meet our needs and budget. We use ac for about 3 to 3 1/2 months per year at a cost of about $300 per year. The electrical rate varies though the day from 8 cents to 12.7 and peak at 18 cents per kW. I run the system up to 11 am when the peak rate kicks in and try not to run it during the peak which ends at 5 pm. The new system will only save us about 50% of our ac bill so I will run this system until it needs replacement. We don’t have the second meter option for ac as they do in some USA states.

    Here is one point that I want to make. It takes about 20 min of operation before you start to dehumidify so turning you system on for 1/2 hr is a waste of time. We tried to run the system at the lowest electrical rate which is after 7 pm. This also utilises the drop in temperature that may occur at night. If the due point or humidity does not drop much as was the case this summer, it is better to keep your windows closed. We also have train issues at night as they love to blast the horn up to 13 times. We live in the middle between two rail lines.

    Here is my second point: To lower your humidity, your evaporator coil (the one in the furnace) must not be much larger than you condenser and the condenser must NEVER be larger than your evaporator to prevent ice build up. Example: for a 2 1/2 ton ac use a 2 1/2 to 3 ton evaporator. They may try to sell you a 3 to to 3 1/2 ton evaporator. For maximum humidity removal, you must first saturate you evaporator with water. Balance your system and watch the components that you buy. Try to install the condenser in a shaded area. Always install a new ECM motor in your furnace or air handler. Use a programmable thermostat. I even time shifted when or refrigerators operate out side of the peak hours cutting our peak electrical demand in half.

    Keep your house in the shade and close blinds on windows. I put boards over our southern skylights until the cooling season was over and then removed the boards. Keep good circulation in your attic. Our roof is mostly covered with solar panels when keeps the attic cooler and prevents the roof from getting hot, extending the life of the roof greatly. It is the sun and uv light that destroys your roof.

    Our next move may be to increase insulation in attic from R20 to R40 depending on cost.

    Reply
  • Amanda December 15, 2016, 5:05 am

    Does anyone have suggestions for people who work overnight (house usually empty at night = questionable to leave windows open?) and sleep during the day?

    I find it very difficult to sleep in hot, humid weather (science will back me up on this one), leaving me feeling terrible for work. I used to be comfortable leaving the AC off most of the year at our previous home in Tampa, FL (working days, often at home)… and strangely enough, I’ve struggled much, much more in Columbus, OH with keeping cooling costs down while sleeping during the day… It will be a while before a different shift becomes a fantastic option, but eventually that will be a possibility… Thanks!

    Reply
    • Mr. Money Mustache December 15, 2016, 9:12 am

      Hi Amanda,

      In that situation, I’d probably
      a) set up my sleeping quarters in the coolest bedroom in the house. A nice finished basement was always my preference for times when I was trying to live a summer night-owl lifestyle, because it’s also dark and quiet!
      or,
      b) get a really new, quiet, efficient window (or ducted) air conditioner and run it to cool just the room I’m sleeping in. This uses very little power, especially if you just need to keep the temperature at a comfortable summer level, like 78-80 with low humidity.

      Reply
  • FMaz January 10, 2017, 3:10 pm

    I lived in British Columbia, were the summer days could be hot and the night cooler.

    I was also in a town house, so heat rising was an issue in the summer AND the winter (were the basement would be at 12C and the top story, where the bedrooms are, were waayyy to warm)

    Anyhow, I bought a Nest (a programmable thermostat). The thing cost me $300, but just by understanding how heat works, I saved that $300 in 2 months.

    Life lesson : make sure you program your thermostats.

    (Now I don’t have to bother with AC were I’m at… Hint: the C and F reads the same ATM)

    Reply
  • Natasha January 26, 2017, 5:01 pm

    This one strikes a nerve. I am not a fan of AC unless I am sweating. And I dont like it on for more than it takes to cool the air down just enough so that I’m not sweating anymore. I live in the northeast and people are STUPID with their overuse of AC here even though everyone complains about how cold and long our winters are. Then at home my husband is an AC addict and I find myself bundling up in the SUMMER in my own house or going outside to warm up. My problem is that in the spring we have crazy allergies and I’m forced to close all the windows so I’m not a runny nosed sneezing red itchy eyed mess in my own home and I resort to putting the AC on. What would you do about that? Last year I doubled up on allergy pills so I will try open windows again. Wish me luck.

    Reply

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