It is the argument that runs in every Alberta household from June to August. One person turns the air conditioner off before work, insisting there is no point cooling an empty house. The other turns it back on, insisting it costs more to drag the temperature back down than it would have to just leave it running. Only one of them is right, and the physics is not close.
The Short Answer
No. Leaving your air conditioner running at full cooling all day while nobody is home costs more than setting it back and letting the house warm up. Turning it completely off for a hot Edmonton workday is also not ideal. The right answer is the boring middle one: set it back, do not shut it down.
Why The “It Costs More To Cool It Back Down” Myth Feels True
The intuition is that your air conditioner has to work extra hard to recover, and that this catch-up burst wipes out whatever you saved. It feels right because you can hear it — the unit runs a long, uninterrupted cycle when you get home, and long cycles feel expensive.
But heat does not move into your house at a constant rate. It moves faster the bigger the difference between inside and outside. A house sitting at 22 °C while it is 30 °C outside is pulling in heat across an 8-degree gap, all day, and your air conditioner is paying for every bit of it. Let that same house drift up to 27 °C and the gap shrinks to 3 degrees. Less heat comes in. There is less heat to remove later.
The recovery cycle is real and it is long. It is simply smaller than the eight hours of continuous heat gain you avoided. You are not getting something for nothing — you are refusing to fight a battle while nobody is in the building.
What Natural Resources Canada Actually Recommends
Federal guidance is specific, and most Alberta homes are nowhere near it.
- 22 to 25 °C when you are home. NRCan notes that a setting at the higher end of that range results in lower air-conditioning costs.
- About 28 °C when the space will be empty for more than four hours. That is a setback, not a shutdown.
- Off entirely if you will be gone more than 24 hours — a long weekend at the lake, not a workday.
- Lower humidity buys you degrees. NRCan points out that when humidity is lower, you can sit comfortably at the higher end of the temperature range. Running bathroom exhaust fans when you shower does more for perceived comfort than dropping the thermostat a degree.
Here is the uncomfortable part. Statistics Canada found in 2025 that Canadian households with air conditioning set an average summer thermostat temperature of 21.3 °C — below the bottom of the federal recommendation. We are, collectively, cooling our homes harder than the government suggests is necessary, and then arguing about whether to turn it off while we are at work.
Alberta has an advantage most of Canada does not: our nights actually cool off. NRCan explicitly endorses the strategy — natural ventilation of the house at night when it is relatively cool, combined with closing the house up during hot days and running the central air conditioner. Open the windows once the outdoor temperature drops below the indoor temperature, run a fan to flush the day’s heat out, then close everything by early morning and let the air conditioner hold a house that started the day cool. A Spruce Grove home that begins the afternoon at 20 °C has hours of thermal cushion before the compressor ever needs to run hard. A Toronto home in August does not get this option. Use it.
Where The Myth Has A Grain Of Truth
Two situations genuinely complicate the simple answer, and both are worth knowing.
Humidity. Your air conditioner removes moisture as a side effect of cooling, and it only does that while it runs. Let a house sit warm and closed all day and you can return to air that is technically cool but feels clammy, because the system has not been dehumidifying. In most of Alberta this matters far less than it does in Ontario or the Maritimes — our summer air is comparatively dry — but during a humid stretch after heavy rain, a smaller setback is more comfortable than a large one.
Oversized equipment. If your air conditioner is too big for the house, deep setbacks punish you. NRCan is direct about this: oversizing “will result in short operating cycles, which will not adequately remove humidity, resulting in an unpleasantly cold and damp home.” An oversized unit slams the temperature down, shuts off, and never runs long enough to wring moisture out of the air. If your house cools fast but always feels damp, the equipment is the problem, not your thermostat habits.
What Canadians Actually Do
Statistics Canada asked. The answers suggest most of us are leaving money on the table for absences that are easy to plan for.
- 51% turn the A/C off or down for a vacation of a week or more. Prairie households, at 56%, were among the most likely to do it.
- 28% do it for a weekend away. Nearly three-quarters of us cool an empty house for two full days.
- 26% of working-age adults do it during a typical day at work or school. This is the single biggest missed opportunity, and it is the one a $60 programmable thermostat solves permanently.
- 82% who do set back say the reason is avoiding wasted energy — not the bill. The bill is a bonus.
Let A Thermostat Win The Argument
The reason this debate persists in so many households is that manual setbacks require someone to remember, twice a day, forever. Nobody does. A programmable or smart thermostat removes the human entirely: 25 °C when you are home, 28 °C from the time the last person leaves, and a recovery that starts before you walk in the door so you never actually experience the warm house you paid nothing to avoid.
The setback is only worth what the equipment can deliver, though. A thermostat cannot fix a filter that has not been changed since March, or an outdoor coil packed with cottonwood fluff, or an indoor coil furred with dust. NRCan warns that even a small loss of refrigerant causes a significant drop in efficiency. A dirty, restricted, undercharged system runs longer to hit the same setpoint — which means every hour of cooling you were trying to save costs more than it should have.
The Practical Rule
- Out for the workday? Set back to about 28 °C. Do not shut it off.
- Out for a weekend? Same setback, or slightly higher.
- Gone more than 24 hours? Turn it off, per NRCan.
- Home and comfortable? Try 24 or 25 °C before you try 21. Most people cannot tell the difference once humidity is controlled, and the bill certainly can.
- Cool night in the forecast? Flush the house overnight, close it by morning, and let the air conditioner coast.
Leaving it running all day is not thrift. It is paying, hour after hour, to hold a temperature difference that nobody is in the house to enjoy.
Quick Answers
Is it cheaper to leave the air conditioner on all day or turn it up when I leave?
It is cheaper to set it back. Heat flows into your house faster when the difference between indoor and outdoor temperature is larger, so a house held at 22 °C all day absorbs more heat than one allowed to drift up to 27 °C. The longer recovery cycle when you get home is real, but it is smaller than the heat gain you avoided during the hours nobody was there. Natural Resources Canada recommends about 28 °C when a space will be empty for more than four hours.
Should I turn my air conditioner completely off when I go to work?
No. Natural Resources Canada recommends turning it up to about 28 °C when a space will be unoccupied for more than four hours, and turning it off entirely only if it will be unoccupied for more than 24 hours. A full shutdown on a hot day lets the house and everything in it soak up heat, and it stops removing humidity.
What temperature should I set my air conditioner to in Alberta?
Natural Resources Canada recommends an indoor thermostat setting in the range of 22 to 25 °C, with the higher end producing lower cooling costs. Statistics Canada found that in 2025 Canadian households with air conditioning averaged 21.3 °C in summer — below the federal recommendation. If your humidity is under control, most people cannot tell the difference between 22 and 25 °C.
Does my air conditioner work harder to cool the house back down?
It runs longer, but that is not the same as costing more. The recovery cycle is one long run at normal efficiency, while leaving the system at full cooling means paying continuously to fight heat that keeps flowing in across a larger temperature gap. The exception is an oversized air conditioner, which short-cycles and fails to remove humidity, producing what NRCan calls an unpleasantly cold and damp home.
Can I just open the windows at night instead?
In Alberta, often yes, and Natural Resources Canada explicitly endorses it: natural ventilation at night when it is relatively cool, combined with closing the house up during hot days and running the central air conditioner. Our overnight lows make this far more effective here than in southern Ontario. Close the windows early in the morning so the air conditioner starts the day with a cool house.
Will a smart thermostat actually save me money?
It saves money mainly by making the setback happen every day without anyone remembering. Statistics Canada found only about 26% of working-age Canadians turn their air conditioning down during a typical day at work or school, so the automation is capturing savings most households are currently skipping. It cannot compensate for a clogged filter, a dirty coil or low refrigerant, all of which make the system run longer to reach the same setpoint.
Trusted Sources
Every figure above is drawn from federal agencies, national statistics or published building-science measurement.
Natural Resources Canada Thermostat Range
The 22–25 °C recommendation, the 28 °C setback, night-ventilation strategy, oversizing and refrigerant loss.
Read the guidanceStatistics Canada 2025 Data
Who uses air conditioning in Canada: 68% of households, an average summer setting of 21.3 °C, and how often we actually set back.
See the dataNRCan — Central Air Conditioners
ENERGY STAR certified central air conditioners in Canada, efficiency ratings and what to look for when replacing.
Compare equipmentU.S. Department of Energy Setbacks
How programmable thermostats and scheduled setbacks reduce heating and cooling energy use.
Read the basicsLinks open official government and industry sites in a new tab. Home Pros Group isn’t affiliated with these organizations.
A Setback Only Saves What Your System Can Deliver
A clogged filter or a coil packed with cottonwood fluff makes your air conditioner run longer for the same temperature. Home Pros Group has kept furnaces, ducts and A/C coils clean across Spruce Grove, Stony Plain and the Greater Edmonton Area since 2003.
This article is general home-energy information, not a guarantee of savings for your specific home or utility rate. Thermostat recommendations, setback guidance, oversizing and refrigerant-loss warnings are summarized from Natural Resources Canada; household air-conditioning and thermostat statistics are from the Statistics Canada Canadian Social Survey released July 8, 2025. Actual savings vary with your home’s envelope, equipment and local weather.