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The biggest, most reliable AC savings come from three things: a sensible thermostat setting, regular maintenance, and sealing obvious air leaks — not exotic technology. Here’s what actually works, in order of impact.
Why Summer AC Bills Climb
Hamilton’s summer humidity, shaped by its Lake Ontario location, means your AC is fighting moisture as well as heat — which is why bills can climb faster here than in a drier climate for the same outdoor temperature. Older HVAC systems, drafty older homes, and inefficient thermostat habits all compound this.
1. Set a Sensible Thermostat Temperature
Around 25–26°C (roughly 77–78°F) when you’re home is a common comfort-and-efficiency balance — set higher when you’re away or asleep. Every degree closer to the outdoor temperature reduces how hard your system has to work.
A smart or programmable thermostat automates this without you having to remember, and geofencing (adjusting based on your phone’s location) backs off cooling automatically when you’re away.
Pair with ceiling fans: moving air lets you comfortably raise your thermostat by 2–3°C without losing comfort, since air movement makes a room feel cooler at the same actual temperature.
2. Keep Up With Maintenance
Neglected maintenance is one of the most common, avoidable causes of rising AC bills:
- Replace or clean filters every 1–2 months during heavy summer use — a clogged filter restricts airflow and forces the system to work harder
- Schedule an annual tune-up before peak season, checking refrigerant levels and cleaning coils
- Clear debris from your outdoor unit — leaves, grass clippings, and general buildup restrict airflow at the compressor
3. Seal Air Leaks and Improve Insulation
- Seal gaps around windows, doors, and ductwork with weatherstripping or caulk — cool air escaping and warm air entering both force your AC to work harder than necessary
- Use heat-reflective window film or blackout curtains during peak sun hours to reduce solar heat gain
- Insulation upgrades are a real, if longer-term, investment — even modest improvements to attic and wall insulation reduce the load on your system meaningfully over a full season
4. Consider an Efficient, Properly Sized Unit
If your AC is over 10–15 years old or consistently struggles to keep up, an ENERGY STAR-certified unit with inverter technology can meaningfully reduce energy use. Sizing matters more than the efficiency rating — an oversized or undersized unit wastes energy regardless of its rating, so this should come from a proper load calculation, not a guess based on square footage.
5. Simple Habits That Add Up
- Avoid heat-generating activities (cooking, running the dryer) during the hottest part of the day
- Close curtains during the day, and open windows overnight if outdoor temperatures drop enough to cool the house naturally
- Dress for the indoor temperature rather than cooling the house to compensate
- Keep doors and windows closed while the AC is running
Rebates
Utility and provincial rebate programs for efficient HVAC upgrades exist but change frequently, and older program names (including some once tied to now-defunct provincial legislation) are no longer current. See our current Ontario rebate guide for what’s actually available today rather than relying on an older source.
Get Help
Contact us for a maintenance visit, a load calculation if you’re considering a new system, or an honest assessment of what’s actually driving your energy bills.
FAQs
Set your thermostat to a sensible temperature when home (roughly 25–26°C) and higher when away, use ceiling fans to feel cooler at a higher setting, keep filters clean, and seal obvious air leaks around windows and doors.
Around 25–26°C during the day when you're home, raised when you're away or asleep. The exact number matters less than consistency — frequent manual overrides waste more energy than a slightly conservative setting left alone.
Every 1–2 months during heavy summer use. A dirty filter restricts airflow and increases energy consumption as the system compensates.
It stops cool air from escaping and warm air from entering, which reduces how hard your AC has to work to maintain the same indoor temperature.
Yes — moving air makes a room feel cooler at the same actual temperature, letting you raise your thermostat by a couple of degrees without losing comfort.
If it's over 10–15 years old, needs frequent repairs, or struggles to cool your home despite regular maintenance, an ENERGY STAR-certified unit with proper sizing can meaningfully improve both comfort and efficiency.
They automate temperature adjustments based on your schedule and location, removing the energy waste of a system left running inefficiently out of habit or forgetfulness.
Yes — cooking adds heat and humidity that your AC then has to remove. Using an outdoor grill or a microwave during the hottest parts of the day reduces this load.
Generally, only run it when needed — turning it off or raising the temperature while you're away saves more energy than running it continuously, provided you're not asking the system to make up a large temperature gap when you return.
A professional load calculation is the reliable way to know — both oversized and undersized units waste energy and perform worse than a properly matched system.
Programs exist through utilities and the province, but they change over time. Check our current Ontario rebate guide rather than relying on an older source for specific figures.
Last reviewed July 2026. Costs, rebate details, and savings estimates in this article are general guidance and change over time — confirm current figures directly before making a decision.