Frost Plug (Cartridge) Block Heater
Also called: freeze plug heater, cartridge block heater, core plug heater
The classic block heater. A heating element replaces one of the engine's frost plugs and warms the coolant directly inside the block — the gold standard for cold starts.
Price
$40–$120 CAD
Wattage
400–1,000 W
Install
Shop recommended
Best for
See verdict
How it works
Every engine block has frost plugs (also called freeze plugs or core plugs) — thin metal discs pressed into casting holes in the block. A frost plug heater replaces one of these discs with an electric heating element that sits directly in the engine's coolant jacket.
When plugged in, the element heats the coolant surrounding the cylinders. Warm coolant rises and circulates by convection, keeping the entire block, the oil in contact with it, and the battery compartment area meaningfully warmer than the outside air. At -30°C, a plugged-in engine can sit at -5 to 0°C — the difference between a groaning, oil-starved crank and a start that sounds like September.
Choosing the right one
Frost plug heaters are engine-specific: the element must match your engine's plug diameter and casting location. This is why fitment guides from Phillips & Temro (Zerostart) and Kat's list a specific part number for nearly every engine sold in Canada. Check our vehicle fitment pages to find yours.
Wattage is matched to engine size — typically 400 W for small four-cylinders up to 1,000 W or more for diesel V8s. More wattage is not better if it's not specified for your engine.
Pros
- Heats coolant directly inside the block — most effective design
- Permanent, invisible, weatherproof once installed
- Factory option on most Canadian-market vehicles uses this design
Cons
- Installation involves coolant drain and tight access — usually a shop job
- Engine-specific part numbers; no universal fit
Installation
Requires removing a frost plug from the engine block and partially draining coolant. Most shops charge $150–$350 including the heater.
Compare with other types