Quick answer
Natural Resources Canada says you don’t need to leave a block heater plugged in overnight — two hours is more than enough. Put it on a timer set to switch on no more than two hours before you start the engine. Using BC Hydro’s Tier 1 rate of 11.87¢/kWh, a heater that draws 400–1,000 W costs roughly 10–24¢ for those two hours (example wattages — check your own heater’s label).
If you drive in cold weather — a cold snap at home, or a trip up to the Interior — you may wonder when to plug in a block heater, for how long, and what it costs. This guide sticks to what Natural Resources Canada (NRCan), BC Hydro and Technical Safety BC actually say. It is general information, not electrical advice. If something about a circuit or outlet worries you, ask a licensed electrical contractor.
What a block heater actually does
According to NRCan, a block heater warms the engine coolant, which in turn warms the engine block and the lubricants. The engine starts more easily and reaches its proper operating temperature faster, and it doesn’t have to work as hard to pump oil through the block.
NRCan explains why that matters: you use more fuel and create more emissions in the first minutes after a cold start than once the engine is at normal operating temperature. The oil is thick in a cold engine, combustion is less efficient, and the air-fuel mixture is richer (more fuel, less air).
NRCan reports that at −20 °C, block heaters can improve overall fuel economy by as much as 10 percent, and for a single short trip at −25 °C the fuel savings could be in the order of 25 percent. Those figures apply at very low temperatures, so don’t expect savings of that size on a mild winter morning.
When to plug in
NRCan does not give a specific outdoor-temperature threshold for plugging in. It describes using a block heater “on cold winter days.” NRCan also notes that temperature has a big effect on fuel use: it cites U.S. EPA estimates that a drop from 24 °C to 7 °C can increase fuel consumption in urban commutes by 12 to 28 percent.
The savings NRCan quotes (10 percent at −20 °C, about 25 percent for one short trip at −25 °C) are for very cold weather, so the clearest payoff is on the coldest mornings. Check your vehicle’s owner’s manual for the maker’s advice for your engine.
If you also need to think about winter traction, see our guide to winter tires in BC.
How long to plug in — the two-hour rule
NRCan’s guidance is clear: you don’t need to leave a block heater plugged in overnight to warm the engine — two hours is more than enough. Use an automatic timer to switch the block heater on two hours before you leave, and for best results set it to turn on no more than two hours before you start the engine. NRCan says this is usually all the time needed to warm the coolant and the engine.
A block heater runs on electricity, so a timer also saves money compared with leaving it plugged in all night.
Tip: If you leave at different times, look for a timer with several on/off settings. The aim is to avoid plugging in at bedtime and leaving it on for hours longer than needed.
What it costs on BC Hydro rates
BC Hydro’s residential tiered rate page lists Tier 1 at 11.87 cents per kWh and Tier 2 at 14.08 cents per kWh. The Tier 1 limit is 22.1918 kWh per day, which BC Hydro says works out to about 675 kWh for a 30-day period. The page also lists a basic charge of 23.44 cents per day, which applies whatever you plug in. Rates change, so check the BC Hydro page for the current figures.
Block heaters differ in wattage; the label or manual for your heater will tell you yours. As an illustration only, here is the arithmetic for three example wattages running for NRCan’s two hours at the Tier 1 rate of 11.87¢/kWh:
| Example wattage | Energy used in 2 hours | Cost per use (Tier 1) |
|---|---|---|
| 400 W | 0.8 kWh | about 9.5¢ |
| 600 W | 1.2 kWh | about 14¢ |
| 1,000 W | 2.0 kWh | about 24¢ |
By the same arithmetic, a 1,000 W heater left on for 10 hours uses 10 kWh, or roughly $1.19 at the Tier 1 rate — five times the two-hour cost, for no extra engine warming according to NRCan. BC Hydro also says that in winter, bills can be up to 66% higher than the rest of the year.
To check your own numbers, use the BC Hydro cost calculator. For context on your overall bill, see our BC Hydro bill explained guide.
Extension cord and power bar safety
The Technical Safety BC article “Ask a safety officer: how to prevent electrical fires” doesn’t mention block heaters, but its general points are worth knowing before you run a cord to your vehicle:
- Check that it is approved for use in Canada. The article makes this point about power bars: what matters most is whether the product is approved for use in Canada, and an unapproved one is a safety hazard and may be an electrical fire risk.
- Read the instructions. Technical Safety BC says many products come with installation instructions explaining whether you can or cannot plug them into a power bar or extension cord. It lists energy-sensitive items such as portable heaters, air conditioners, fridges and hotplates as things that can never be plugged into power bars or extension cords. Check your block heater’s instructions and your vehicle manual for what they say about cords.
- Don’t overload a power bar. The article says most 120-volt power bars are rated for a maximum load of 12 amps, and that a 1,300-watt toaster plus a 1,100-watt coffee maker on one bar already comes to a combined load of 20 amps.
- Watch for overheating. Scorch marks or a device that feels warm to the touch are warning signs; unplug your items immediately. If you are unsure why it is happening, contact a licensed electrical contractor.
- If a breaker keeps tripping, stop resetting it. Technical Safety BC says a tripping breaker means something is wrong in the circuit, and continuing to reset or replace it is an electrical fire hazard.
Safety: If a cord, plug or outlet gets hot, shows scorch marks, or a breaker keeps tripping, stop using it and call a licensed electrical contractor.
Installation
Our official sources don’t cover installing a block heater or a new outdoor outlet. Check your owner’s manual or ask a qualified mechanic about a heater for your engine, and use a licensed electrical contractor for any new outlet or circuit work.
Idling isn’t a substitute
NRCan says excessive idling is not an effective way to warm up your vehicle, even in cold weather: the best way to warm it up is to drive it. With today’s computer-controlled engines, it says, no more than two to three minutes of idling is usually enough warm-up time before you start driving. NRCan also says any more than ten seconds of idling uses more fuel than restarting the engine, and as a guideline, if you’re stopped for more than 60 seconds — except in traffic — you should turn the engine off.
Frequently Asked Questions
What temperature should I plug in my block heater at?
NRCan doesn’t set a specific threshold. It recommends block heaters on cold winter days, and the fuel savings it quotes are for −20 °C and −25 °C. Your owner’s manual may give guidance for your engine.
How long should I plug in my block heater?
About two hours. NRCan says to put the heater on a timer set to turn on no more than two hours before you start the engine, and that two hours is more than enough to warm the coolant and the engine.
Do I need to leave a block heater plugged in all night?
No. NRCan says you don’t need to leave a block heater plugged in overnight to warm the engine. Leaving it on longer just uses more electricity.
How much does it cost to run a block heater in BC?
It depends on your heater’s wattage. At BC Hydro’s Tier 1 rate of 11.87¢/kWh, a 400–1,000 W heater running two hours uses 0.8–2.0 kWh, which works out to about 10–24¢. Plug your own numbers into the BC Hydro cost calculator.
Can I use a power bar or extension cord for a block heater?
Check the instructions that came with your block heater and vehicle. Technical Safety BC says some energy-sensitive items, such as portable heaters, can never be plugged into power bars or extension cords, and that any cord or power bar should be approved for use in Canada. Its article doesn’t mention block heaters specifically, so if you are unsure, ask a licensed electrical contractor.
What should I do if the breaker keeps tripping?
Stop resetting it. Technical Safety BC says a tripping breaker means there is something wrong in the circuit, and continuing to reset it is an electrical fire hazard. Contact a licensed electrical contractor.
Official sources
- Natural Resources Canada — Factors that affect fuel efficiency (block heater timer guidance)
- Natural Resources Canada — Block Heaters Save Fuel and Help the Environment
- Natural Resources Canada — Idling: Ready to Use Facts
- BC Hydro — Residential tiered rate
- BC Hydro — Understanding your winter bill
- Technical Safety BC — How to prevent electrical fires
General information only, not professional advice. Rules and prices change, so check the official sources above before you act. Spotted something out of date? Tell us.