Block heaters in Calgary: when to plug in, and for how long

When to plug in

The Alberta Motor Association’s (AMA) rule is to plug in once it is colder than −15 °C; above that, it says, most vehicles manage without. AMA adds that an older vehicle, or one with maintenance problems, may need plugging in at a milder temperature. CAA’s winter checklist is softer: below −15 °C, it suggests considering a block heater to ease the strain on the engine. CAA-Quebec starts earlier, suggesting you plug in once it falls below −5 °C and calling it highly recommended at −15 °C or colder. Natural Resources Canada (NRCan), whose block heater advice is about timing and fuel, names no temperature.

In Calgary, −15 °C is no rare event. Environment and Climate Change Canada’s 1991–2020 normals for Calgary (Airport) count about 72 days a year with a low below −10 °C and about 22 with a low below −20 °C (ECCC publishes no count for −15 °C itself). In January alone the low drops below −20 °C on about 8 days.

Sources: [2] AMA: using a block heater; [3] AMA, January 2024; [4] CAA: winter car care; [5] CAA-Quebec: block heaters; [1] NRCan: fuel efficiency; [6] ECCC climate normals

How long to plug in for

Not all night. Beyond that the sources disagree, and AMA’s own pages give three answers:

• NRCan: have a timer switch the heater on at most 2 hours before you leave. Its former article on block heaters said two hours is normally long enough to warm the coolant and the engine.
• AMA: about 4 hours before you expect to drive, on a timer, in its block heater how-to; three to four hours at −15 °C or colder in its January 2024 and December 2021 cold-weather releases and in AMA Insider; and at least four hours below −15 °C in its article on block heaters and batteries and in a December 2021 holiday release.
• CAA-Quebec: three to four hours ahead is plenty, with no need to leave it on overnight.

AMA’s “at least four hours” and NRCan’s “no more than 2 hours” cannot both be followed: they are different advice, not one rule in different words. Either way, a timer does the work. The evaluation of an Ontario block heater timer program notes that heaters left on overnight run for about 12 hours, while engines typically need no more than four.

Don’t idle to warm up

Plugging in replaces idling. NRCan says idling beyond 30 seconds does the car no good, and ten minutes of it burns 0.25 to 0.50 L of fuel. A few minutes of gentle driving warms the engine, the drivetrain and the cabin faster than standing still, it says.

Sources: [1] NRCan: fuel efficiency; [7] NRCan, archived; [2] AMA: using a block heater; [3] AMA, January 2024; [8] AMA, December 2021 (plugging in); [9] AMA Insider: block heaters; [10] AMA: block heaters and batteries; [11] AMA, December 2021; [5] CAA-Quebec: block heaters; [12] IESO evaluation, 2022

What a block heater saves

Cold oil is thick and slow to circulate, so a cold engine needs more effort to turn, and its fuel burns less efficiently, NRCan’s archived block heater article explained. That article put the gain from a block heater at up to 10 percent of overall fuel economy at −20 °C, and about 25 percent on one short trip at −25 °C. NRCan no longer publishes it; its current page says only that block heaters cut fuel use and emissions.

The battery gains too. AMA says plugging in eases the strain on the battery and helps the engine turn over, and that its roadside calls for batteries almost double over the winter. The car battery guide covers testing, boosting and replacing one.

Sources: [7] NRCan, archived; [1] NRCan: fuel efficiency; [10] AMA: block heaters and batteries

What it costs to run

No Alberta utility or government page we found publishes how much power a block heater draws. The one public figure is from the evaluation of an Ontario block heater timer program, which assumed 0.511 kW, an estimate taken from an earlier pilot. The same report notes that this is much lower than the 0.8 to 1.5 kW in the U.S. technical reference manuals it compared, so treat 0.511 kW as the low end: a heater that draws 1.5 kW costs about three times as much to run.

At 0.511 kW to 1.5 kW, and at the energy charge of ENMAX’s Rate of Last Resort in Calgary, 12.06¢ per kWh until December 31, 2026:

• NRCan’s 2 hours on a timer: 1.0 to 3.0 kWh, about 12¢ to 36¢ of energy.
• AMA’s 4 hours: 2.0 to 6.0 kWh, about 25¢ to 72¢ of energy.
• All night, about 12 hours: 6.1 to 18.0 kWh, about 74¢ to $2.17 of energy.

These are energy charges only. The Alberta Utilities Commission notes that the energy charge leaves out delivery to your home and the retailer’s administration fee, and a retail contract has a rate of its own. ENMAX says the Rate of Last Resort may move by up to 10 percent after December 31, 2026.

Sources: [12] IESO evaluation, 2022; [13] ENMAX: Rate of Last Resort; [14] AUC: Rate of Last Resort

Kinds of engine heater

AMA’s automotive expert describes three:

• A standard block heater, which heats the engine coolant, and through it the engine and its oil. CAA-Quebec calls the coolant type the most common and the most effective.
• A recirculating coolant heater, which keeps the coolant moving while it heats it.
• An oil pan heater: a heating element fixed to the oil pan, common on German cars.

Battery warmers and dipstick heaters are sold too, but none of the sources this guide relies on describes them, so it does not either.

Sources: [9] AMA Insider: block heaters; [5] CAA-Quebec: block heaters

Does your car have one?

AMA says most vehicles sold new in Alberta already have a block heater, and CAA-Quebec notes that many automakers fit them at the factory. Cars brought in from other provinces often lack one. Look under the hood: a plug-in cord there is the giveaway, AMA says.

Which heater suits a car depends on the car, so AMA’s advice is to ask your mechanic which to fit, and have a shop install it.

Sources: [9] AMA Insider: block heaters; [5] CAA-Quebec: block heaters

Cords and outlets

The fire-safety and utility advice on plugging in a car comes down to a few rules:

• Use an outdoor-rated extension cord whose wattage rating covers the heater.
• Give each car its own cord and its own outlet.
• Unroll the cord completely while it is in use; a cord left coiled can overheat.
• Keep cords out from under mats and rugs, and out of doorways.
• Throw out a cracked or damaged cord instead of taping it, and replace any cord you have driven over or pulled out of the driveway while it was still plugged in.
• Never plug in a car while it is parked inside a garage.

Sources: [15] City of Calgary: electrical safety; [16] Manitoba Hydro

Electric vehicles: precondition instead

An electric car has no engine block to warm. CAA’s advice is to heat the cabin while the car is still on the charger, timing that preconditioning to your departure where the car can do it, to get the most range and comfort. In CAA’s winter road test the electric cars covered 14 to 39 percent less distance than their official range.

Electric cars and hybrids still carry a 12-volt battery that the cold can drain; the car battery guide explains how to boost one safely.

Source: [17] CAA: EVs in winter