Inline Coolant Heater
Also called: circulation tank heater, lower rad hose heater, in-line heater
Installed in a coolant hose rather than the block itself. Thermosiphon and pump-style versions circulate warmed coolant through the whole engine.
Price
$60–$180 CAD
Wattage
600–1,500 W
Install
DIY-moderate
Best for
See verdict
How it works
An inline heater splices into the cooling system's plumbing — commonly the lower radiator hose or a heater hose. Basic models rely on thermosiphon circulation: heated coolant rises through the engine while cooler coolant sinks back to the heater, creating a slow natural loop.
Pump-equipped circulation heaters (common on diesels and fleet trucks) actively push warm coolant through the block and heater core, warming the engine faster and more evenly — some drivers wake up to a cab that blows warm air within a minute of starting.
When to choose inline over frost plug
If your engine has no available frost-plug element, an inline heater is the next best permanent option. They're also the standard upgrade path for diesel pickups in the Prairies, where a 1,000–1,500 W circulating heater keeps a big block genuinely warm overnight at -35°C.
Pros
- Effective whole-engine warming, especially pump models
- More DIY-friendly than a frost plug swap
- Higher wattage options for big diesels
Cons
- Hose splices are a potential leak point if poorly clamped
- Thermosiphon models must be mounted low and oriented correctly
Installation
Splices into a heater hose or lower rad hose. Handy DIYers can do it in an afternoon; shops charge $100–$250.
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Amazon buying options
Zerostart 3308002 circulation heater, 1,000 W
CSA-approved Series 8000 inline circulation heater with 5/8-inch hose fittings, from the factory block-heater people. The light-duty size for pickups and vans.
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Amazon buying options
Kat's 13150 circulating tank heater, 1,500 W
Plumbs into a heater hose and thermosiphons hot coolant through the whole engine — the serious option for big diesels, tractors, and equipment with no frost-plug access.
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Check the fitment for your own vehicle
Most passenger vehicles take a frost-plug element rather than this style. The fitment pages say which one your engine actually accepts.
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