Ontario's Ultra-Low Overnight Rate
Can cheap overnight electricity lower your heat pump running costs? How the plan works, who saves, who should skip it, and how to set up your system.
The short answer: Ontario's ultra-low overnight rate charges very little for electricity from 11 p.m. to 7 a.m. every day, but much more on weekdays from 4 p.m. to 9 p.m. It can lower heat pump running costs if you shift heavy loads such as EV charging and water heating overnight, or if a dual-fuel system lets your gas furnace take over at peak. Households that run a heat pump hard on weekday evenings may pay more. Compare your own usage with the OEB bill calculator before you switch.
More York Region homes now heat with electricity, thanks to cold-climate heat pumps, hybrid systems and electric vehicles in the driveway. That makes your electricity price plan matter more than it used to. Ontario's ultra-low overnight rate, called the Ultra-Low Overnight (ULO) price plan by the Ontario Energy Board, rewards households that can shift electricity use into the night. For a heat pump owner, the question is whether a system that runs around the clock can really benefit.
This guide explains how the ultra-low overnight rate works, how it compares with Time-of-Use and Tiered pricing, what it means for heat pumps in winter, and the setup that gives you the best chance of saving. If you are weighing a heat pump in the first place, start with our heat pump page.
Key takeaways
- The ULO plan has the cheapest overnight price and the most expensive weekday evening price of any Ontario plan.
- Heat pumps run steadily, so savings depend on what else you can move overnight.
- EV charging, timed water heating and dual-fuel switching make the plan work best.
- Large setbacks are rarely a good idea with heat pumps; gentle pre-heating works better.
- Prices change every November 1 and May 1, so recheck the numbers each season.
How the Ultra-Low Overnight Rate Works
The ULO plan splits the week into four price periods. The Ontario Energy Board sets the prices twice a year, on November 1 and May 1. The table below uses the prices that took effect on November 1, 2025 as an example; check oeb.ca for the current numbers.
| ULO period | When | Example price (Nov 2025) |
|---|---|---|
| Ultra-low overnight | Every day, 11 p.m. to 7 a.m. | 3.9 ¢/kWh |
| Weekend off-peak | Weekends and holidays, 7 a.m. to 11 p.m. | 9.8 ¢/kWh |
| Mid-peak | Weekdays, 7 a.m. to 4 p.m. and 9 p.m. to 11 p.m. | 15.7 ¢/kWh |
| On-peak | Weekdays, 4 p.m. to 9 p.m. | 39.1 ¢/kWh |
In that example, overnight power cost about one-tenth of on-peak power. That gap is the whole point of the ultra-low overnight rate: it rewards households that move flexible loads away from weekday evenings.
Ultra-Low Overnight Rate vs Time-of-Use vs Tiered
| Plan | How you pay | Best fit |
|---|---|---|
| Time-of-Use (TOU) | Three periods; on-peak is moderate (20.3 ¢/kWh in the November 2025 example) | Most households; the default plan |
| Tiered | One price up to a monthly threshold, a higher price above it (winter threshold 1,000 kWh) | People home all day with steady, modest use |
| Ultra-Low Overnight (ULO) | Very cheap nights, very expensive weekday evenings | EV owners and homes that can shift big loads overnight |
Residential customers can switch plans by contacting their local utility. The OEB's bill calculator lets you test your own usage against each plan first.
What the Ultra-Low Overnight Rate Means for Heat Pumps
A cold-climate heat pump works best when it runs steadily at low speed. Unlike an EV, it cannot simply do all its work between 11 p.m. and 7 a.m. On cold weekday evenings, it will still need power during the 4 p.m. to 9 p.m. on-peak window, when the ULO price is highest. That is why the ultra-low overnight rate is not an automatic win for every heat pump home.
It can still pay off in three common situations:
- You also charge an EV. Overnight charging is often the biggest single load a home can shift, and it can outweigh higher evening heating costs.
- You have a dual-fuel (hybrid) system. A smart thermostat can let the gas furnace handle heat during weekday on-peak hours and the heat pump take over the rest of the day.
- You can pre-heat gently. Raising the set point a degree or two before 4 p.m. and easing back during the peak lets the house coast through the most expensive hours. Well-insulated homes coast best.
Avoid deep night-time setbacks with a heat pump. A big recovery in the morning can trigger expensive electric backup heat. Our guide to recommended thermostat settings covers sensible targets, and our article on how extreme cold affects heat pump performance explains backup heat.
Who Saves and Who Should Skip It
| Likely to save on ULO | Likely better on TOU or Tiered |
|---|---|
| Homes that charge an EV overnight | Homes where everyone is home cooking, laundering and heating from 4 to 9 p.m. |
| Dual-fuel heat pump and furnace systems | All-electric homes with older, leaky envelopes |
| Households that run dishwashers, laundry and dryers overnight | Anyone who cannot change daily routines |
| Homes with timer-controlled electric water heating | Homes with electric baseboard heat as the main source |
Setting Up Your Heating for the Ultra-Low Overnight Rate
A few equipment choices make the ultra-low overnight rate far easier to live with:
- A compatible smart thermostat with scheduling and, for hybrid systems, the ability to switch between heat pump and furnace.
- A correctly set balance point on dual-fuel systems, so the furnace takes over when it is cheaper or more comfortable.
- Right-sized equipment. An undersized heat pump leans on backup heat at exactly the wrong times. See our guide to heat pump installation for how sizing is done.
- Yearly maintenance to keep coils clean and defrost working, which protects efficiency in the coldest weeks.
If you want to understand the bigger picture of operating costs and rebates, read our guide to heat pump costs and rebates in Ontario, and if your bills already feel high, start with why your heating bill may be too high.
Water Heating, EVs and the Ultra-Low Overnight Rate
For many homes, the real savings on the ultra-low overnight rate come from loads that are easy to time. An electric vehicle can be set to charge only after 11 p.m. through the car or the charger app. A heat pump water heater or electric tank can be put on a timer so most reheating happens overnight, as long as the tank is large enough to cover evening showers. Dishwashers, washers and dryers with delay-start buttons can also run while you sleep. Add these together and a household can move a large share of its electricity use into the cheapest hours, which helps offset what the heat pump uses during the evening peak.
6 Steps to Decide If the Plan Fits Your Home
- Log in to your utility account and download at least a few months of hourly usage, ideally including winter.
- Note how much of your use falls on weekdays between 4 p.m. and 9 p.m.
- List the loads you can move overnight: EV charging, dishwasher, laundry, water heating.
- Run your numbers through the OEB bill calculator for ULO, TOU and Tiered.
- If you heat with a hybrid system, ask your HVAC contractor to set the thermostat to favour gas during on-peak hours.
- Recheck after each price change on November 1 and May 1, and switch back if the ultra-low overnight rate no longer works for you.
How Aire One Helps You Get More From Off-Peak Power
Aire One has installed heating and cooling systems across Markham, Richmond Hill and York Region since 1990, including cold-climate heat pumps, dual-fuel systems and smart thermostats. We size equipment with a proper heat-loss calculation, set up controls to match your price plan, and back installations with a 10-year worry-free warranty. Talk to our Markham HVAC team about the right setup, or keep your system efficient with a maintenance and protection plan.
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Frequently Asked Questions
What hours is the ultra-low overnight rate in Ontario?
The ultra-low overnight period runs every day from 11 p.m. to 7 a.m. On weekdays, the most expensive on-peak period runs from 4 p.m. to 9 p.m. Weekends and holidays from 7 a.m. to 11 p.m. are billed at the weekend off-peak price.
Is the ULO plan good for heat pumps?
It can be, but it is not automatic. Heat pumps run steadily, including on weekday evenings when ULO prices are highest. The plan works best when you also shift EV charging or other large loads overnight, or when a dual-fuel system lets the gas furnace cover the on-peak hours.
How do I switch to the ultra-low overnight plan?
Contact your local electricity utility, which handles price plan changes. Before switching, use the Ontario Energy Board's bill calculator with your own usage history to compare the ULO, Time-of-Use and Tiered plans.
Should I turn my heat pump down at night on the ULO plan?
Usually not by much. Overnight is the cheapest time to run a heat pump on this plan, and large setbacks can trigger costly backup heat when the system recovers. A small, steady schedule with gentle pre-heating before the evening peak works better.
How often do Ontario electricity prices change?
The Ontario Energy Board sets regulated electricity prices twice a year, on November 1 and May 1. Recheck your numbers after each change to make sure your plan still suits how your home uses power.
Sources and Helpful Resources
- Ontario Energy Board: Electricity Prices Effective November 1, 2025
- Ontario Energy Board: Choosing Your Electricity Price Plan
- Natural Resources Canada: Electric Heat Pumps
- Save on Energy: Home Renovation Savings Program
Matthew leads the Aire One Markham and Metro Toronto team, helping York Region homeowners choose heat pumps and controls that keep running costs predictable. Aire One has been a TSSA-registered, Carrier Factory Authorized Dealer since 1990.