By Mario Vaghei, General Manager, Aire One Peel Heating & Cooling · Published July 3, 2023 · Facts verified August 31, 2026
Most air conditioner myths survive because they were true in 1995. Equipment changed, the Ontario electricity rate structure changed, and the sizing rules in our Building Code are stricter than most homeowners realise. Below are the six cooling myths we hear most across Peel Region, what the primary sources actually say, and what each one costs you. One of them is repeated by nearly every article on this subject, including Google's own AI summary, and it is flatly wrong for the equipment we install today.
In this guide
All six myths at a glance · Does a lower setting cool faster · Single-stage, two-stage, variable-speed · Leaving it on all day · Closing vents · Do fans cool a room · Is bigger better · Maintenance · FAQ · Final verdict
Short answer
The most expensive air conditioner myths in Ontario are that a lower thermostat setting cools faster, that leaving the system running all day is cheaper, that closing vents saves energy, and that a bigger unit is better. None of them hold up, and the sizing myth conflicts with the calculation method our Building Code requires.
The table below pairs each myth with what the primary source actually says.
Key takeaways
- A thermostat is a target, not a throttle. Setting 16 degrees instead of 23 does not speed anything up, it just stops the system later.
- "Air conditioners run at one fixed speed" is only true of single-stage units. Two-stage and variable-speed equipment modulates, and most myth articles have not caught up.
- Natural Resources Canada puts a number on the fan question: two degrees higher plus a ceiling fan cuts cooling costs by nearly 14 per cent.
- Oversizing is not just wasteful in Ontario. The Building Code requires cooling capacity to be calculated to CSA F280.
All six air conditioner myths, and what the source actually says
Six myths cover almost every cooling misunderstanding we meet on service calls: that a lower setting cools faster, that running all day is cheaper, that closing vents saves energy, that fans cool rooms, that bigger equipment is better, and that maintenance can wait until something breaks. The table below pairs each with the primary source that settles it.
| The myth | What is actually true | What it costs you |
|---|---|---|
| A lower setting cools the room faster | The setpoint is a stopping point, not a speed control | Overcooling and a longer run past the temperature you wanted |
| Leaving it running all day is cheaper | Raising the setpoint while you are out costs less; NRCan measures two degrees plus a fan at nearly 14 per cent | Cooling an empty house through the costliest hours of the day |
| Closing vents in unused rooms saves energy | It raises duct static pressure; the blower still moves air against a smaller opening | Uneven temperatures and extra strain on the blower |
| Fans cool a room | NRCan: fans "only cool the occupants in the room by circulating the air" | Fans left running in empty rooms, using power for nothing |
| A bigger unit cools better | Oversized units short cycle and remove less humidity; Ontario requires CSA F280 sizing | A clammy home, more compressor starts, higher install cost |
| Maintenance can wait until it fails | NRCan: change filters regularly and keep coils and ductwork clear of dust and dirt | Reduced capacity, and a breakdown in the week you need it most |
Does setting the thermostat lower cool the room faster?
Setting the thermostat lower does not cool a room faster, because the setpoint tells the system when to stop, not how hard to work. Set 16 degrees Celsius when you want 23 and the room still passes through 23 at exactly the same moment. The only difference is that the system keeps running afterwards, overcools the space, and bills you for it.
That much every article agrees on. The reason almost all of them give, however, is wrong.
The correction: most myth articles, and Google's own AI summary of this question, explain it by saying air conditioners "run at one fixed speed" or "cool at a fixed, steady rate". That is only true of single-stage equipment. Carrier's own documentation describes a two-stage unit running a low stage at "roughly 65% capacity" and a variable-speed unit that "modulates its output in 1% increments, operating anywhere from 30% to 100% capacity". If you bought a modern system in the last few years, the fixed-speed explanation does not describe your equipment.
Single-stage, two-stage and variable-speed: what actually changes
The three compressor types differ in how many capacity levels they can run at, which is exactly why the "fixed speed" shorthand breaks down. A single-stage unit is on or off. A two-stage unit adds a low stage. A variable-speed unit modulates continuously, and it is that long, slow running that removes humidity.
| Compressor type | How it runs | Effect on humidity |
|---|---|---|
| Single-stage | "Entirely on or completely off" | Shorter cycles, least moisture removed |
| Two-stage | High stage 100 per cent, low stage roughly 65 per cent | Longer runs at low stage remove more moisture |
| Variable-speed | Modulates in 1 per cent increments, 30 to 100 per cent | Longest run times and the best humidity control |
The practical consequence is worth stating plainly, because it cuts against the usual advice. On a variable-speed system a large gap between the room temperature and the setpoint can push the compressor to a higher output than a small gap would. So an aggressive setting is not literally ignored. It still does not get you to your comfortable temperature any sooner, and it guarantees the system carries on past it, which is why the advice to set a sensible number and leave it alone survives the correction intact. Our guide to optimal air conditioning settings covers where to land.
Is it cheaper to leave the air conditioner on all day?
It is not cheaper to leave the air conditioner cooling an empty house all day; raising the setpoint while you are out costs less. Natural Resources Canada puts a figure on the gentler version of this: "Set your thermostat two degrees higher and use ceiling fans to circulate cool air. This can reduce your air conditioning costs by nearly 14%."
In Ontario there is a second, larger saving available, and it has nothing to do with the equipment. On the Ontario Energy Board's summer Time-of-Use schedule, in effect since November 1, 2025, weekday on-peak electricity runs from 11 a.m. to 5 p.m. at 20.3 cents per kWh, against 9.8 cents off-peak. Cooling the house before 11 a.m. and letting it drift through the afternoon moves the same comfort into the cheaper hours.
| Summer period | Hours | Price per kWh |
|---|---|---|
| On-peak | Weekdays 11 a.m. to 5 p.m. | 20.3 cents |
| Mid-peak | Weekdays 7 to 11 a.m. and 5 to 7 p.m. | 15.7 cents |
| Off-peak | Weekdays 7 p.m. to 7 a.m., plus weekends and holidays | 9.8 cents |
Which distributor you call to change rate plans is not provincial, even though the prices are. Alectra covers Mississauga and Brampton, Hydro One covers Caledon and Bolton, Milton Hydro covers Milton, Halton Hills Hydro covers Georgetown, and Toronto Hydro covers Etobicoke.
Does closing vents in unused rooms save energy?
Closing vents in unused rooms does not reliably save energy, because the blower keeps pushing the same air against a smaller opening. Ductwork is sized for a designed airflow, and shutting registers raises static pressure in the system rather than reducing the work it does. The usual result is uneven temperatures elsewhere in the house and more strain on the blower.
There is an honest caveat here that the myth articles skip. On a system with a variable-speed blower the fan can compensate somewhat, so the penalty is smaller than on a fixed-speed blower, and one closed register in a large house is not a crisis. Closing off several, or shutting the door on a room with a return, is where it becomes a real problem. If some rooms are genuinely never used, the answer is a zoning system or a ductless head, not a stack of closed vents.
Do ceiling fans actually cool a room?
Ceiling fans do not cool a room, they cool the people in it. Natural Resources Canada states it directly: fans "only cool the occupants in the room by circulating the air so switch your fan off when you leave". Moving air speeds evaporation from your skin, which feels cooler, but the thermometer on the wall does not move.
This is the myth with the clearest payoff, because the fix is free. NRCan pairs the fan with a thermostat adjustment and measures the result at nearly 14 per cent off cooling costs. Run the fan while you are in the room, set the thermostat two degrees higher, and switch the fan off on your way out.
Is a bigger air conditioner better?
A bigger air conditioner is not better, and in Ontario the point is stronger than efficiency alone. An oversized unit reaches the setpoint quickly and shuts off before it has run long enough to pull moisture out of the air, which leaves a house that is cold and clammy at the same time. It also starts and stops more often, and compressors take most of their wear at startup, which is one reason a system can fail years earlier than it should. Our guide on when to replace an air conditioner covers the signs.
The Ontario Building Code requires cooling capacity to be determined in accordance with CSA F280, Determining the required capacity of residential space heating and cooling appliances, currently CSA F280:12 (R2025). That is a room-by-room heat gain calculation, not a rule of thumb based on square footage. So "just go a size up" is not a preference in this province, it is a departure from the method the Code points at. Any contractor sizing your system by floor area alone is skipping that calculation.
This is also where we should be honest about our own position. We sell and install air conditioners, so "buy the bigger one" would be the easier sell for us and we are telling you not to. The possible downside of our approach: a properly sized system will not cool a badly insulated house any faster than the calculation says it can, and some homeowners read that as underpowered. It is not. It is the load the house actually has. Our air conditioner installation cost guide shows what the correct size costs in this market.
Can air conditioner maintenance wait until something breaks?
Maintenance cannot sensibly wait until something breaks, because the two most common causes of lost cooling capacity build up gradually and are cheap to prevent. Natural Resources Canada's guidance is short: "Change air filters regularly and keep your coils and ductwork free of dust and dirt to keep your home comfortable." A blocked filter and a dirty condenser coil both make the system work harder for less cooling, and both show up first as a house that will not reach temperature. If yours already will not, start with why an AC is not cooling instead.
The honest version of this myth is that not every task needs a technician. Changing a filter and clearing leaves away from the outdoor unit are homeowner jobs, and doing them costs nothing. A professional visit earns its keep on the parts you cannot check yourself, such as refrigerant charge and electrical connections. Our spring AC checklist separates the two.
| Task | Who does it | Which myth it settles |
|---|---|---|
| Change the filter, clear leaves from the outdoor unit | You, no cost | Maintenance can wait |
| Reopen every closed register, then re-check room temperatures | You, no cost | Closing vents saves energy |
| Set a schedule that pre-cools before 11 a.m. | You, no cost | Running all day is cheaper |
| Check refrigerant charge and electrical connections | Certified technician | Maintenance can wait |
| Run a CSA F280 heat gain calculation before replacing | Contractor, at the estimate | Bigger is better |
Which myth is costing you the most?
Two questions, same answers as the tables above.
How we know this
Every claim on this page traces to a source read on August 31, 2026: fan and filter guidance and the 14 per cent figure from Natural Resources Canada, electricity prices and hour blocks from the Ontario Energy Board, the sizing requirement from the Ontario Building Code and CSA F280:12 (R2025), and compressor staging from Carrier's residential documentation. Where a myth has an honest caveat, such as the variable-speed blower softening the closed-vent penalty, we have said so rather than flattening it. We have not published counted first-party call data on this topic, so this page claims no percentages of our own.
See who you would be calling
Three short videos from our own channel.
Want the sizing done properly?
Book a free in-home estimate and we will calculate the load rather than guess at it. Aire One Peel Heating & Cooling, TSSA-registered fuels contractor FS R0076624709, 1625 Courtneypark Dr E, Mississauga, ON L5T 1V9.
Frequently asked questions
What are some common myths about air conditioning?
The six we meet most often are that a lower thermostat setting cools faster, that running the system all day is cheaper than turning it up, that closing vents in unused rooms saves energy, that ceiling fans cool rooms, that a bigger unit performs better, and that maintenance can wait until something fails. Each one has a measurable cost attached.
Is it better to run the AC all day?
No. Raising the setpoint while the house is empty costs less than holding one temperature all day. Natural Resources Canada measures a two degree increase combined with a ceiling fan at nearly 14 per cent off cooling costs. In Ontario you can add to that by pre-cooling before 11 a.m. and coasting through the on-peak window.
What is the 3 minute rule for aircon?
It refers to waiting roughly three minutes before restarting a compressor after it stops, so that refrigerant pressures equalise and the motor is not asked to start against high head pressure. Most modern thermostats and control boards enforce this delay automatically, which is why a system sometimes appears unresponsive for a few minutes after a power interruption.
Is it healthier to sleep with or without AC?
That depends on the person and the weather, and it is a question for a clinician rather than a contractor. What we can say is that air conditioning may help during extreme heat, and that a clean filter and airflow that is not blowing directly on you make the room more comfortable. This is general comfort guidance and not medical advice.
Do air conditioners really run at one fixed speed?
Only single-stage units do. Carrier describes a single-stage air conditioner as having "two modes: entirely on or completely off", a two-stage unit as running a low stage at roughly 65 per cent capacity, and a variable-speed unit as modulating "in 1% increments, operating anywhere from 30% to 100% capacity". Most articles repeating the fixed-speed claim have not updated it.
How is air conditioner size decided in Ontario?
By calculation, not by floor area. The Ontario Building Code requires heating and cooling capacity to be determined in accordance with CSA F280, Determining the required capacity of residential space heating and cooling appliances, currently the 2012 edition reaffirmed in 2025. It is a room-by-room heat gain calculation that accounts for insulation, windows and orientation.
Does closing AC vents save money?
Usually not. Ductwork is sized for a designed airflow, so closing registers raises static pressure rather than reducing the work the blower does, and the saving people expect rarely appears on the bill. A variable-speed blower softens the penalty, but if whole rooms genuinely go unused the real answer is zoning or a ductless head.
Final verdict
Two of these air conditioner myths cost you money every single day, and both are free to fix: cooling an empty house through the on-peak window, and leaving fans running in rooms nobody is in. The sizing myth costs the most, but only once, at replacement time, which is exactly when it is worth insisting on a real CSA F280 calculation. And treat the "fixed speed" explanation as a signal: an article still repeating it in 2026 is describing equipment that predates most of what we now install.
What we updated
August 31, 2026: full rebuild of the July 2023 article. Corrected the claim that air conditioners run at one fixed speed, which is true only of single-stage equipment. Added the compressor staging table, the Ontario Time-of-Use cost table, the CSA F280 sizing requirement, the distributor list by city, a myth-diagnosis quiz, and six FAQs. All facts re-verified on the date shown in the byline.
Sources and references
- Natural Resources Canada, How to stay cool all summer: ceiling fans cool occupants, and the two degree plus fan saving
- Natural Resources Canada, Beat the heat: filters, coils and ductwork maintenance
- Ontario Energy Board, electricity rates and Time-of-Use hour blocks
- CSA Group, CSA F280:12 (R2025), Determining the required capacity of residential space heating and cooling appliances
- Carrier, single-stage, two-stage and variable-speed air conditioner operation
Mario Vaghei
General Manager, Aire One Peel Heating & Cooling
Mario rebuilt this 2023 article after spotting that its central explanation, that air conditioners run at one fixed speed, is contradicted by the equipment we install. He checked each remaining myth against NRCan, the Ontario Energy Board, CSA F280 and Carrier's documentation on August 31, 2026.