Generator Block Heaters & Cold-Weather Kits
A generator has one job: start when everything else has failed. But the exact weather that knocks the power out — an ice storm, a -35°C snap — is the weather a cold-soaked engine hates most. Thickened oil, a weak battery, and a reluctant air-cooled single all conspire right when the furnace goes dark.
The fix depends on which of the three generator species you own. Standby units (Generac, Kohler, Cummins home units) have factory cold-weather kits. Portable generators have nothing from the factory, but a $30 pad heater solves them. And liquid-cooled diesel gensets are just small tractors — they take a real coolant heater.
What fits, by application
Part numbers from the Zerostart / Phillips & Temro and Kat's application guides where a listing exists. Numbers are occasionally superseded — confirm against a current catalog before ordering.
Portable generators (air-cooled, up to ~10,000 W)
No coolant jacket, so no "block heater" in the traditional sense — heat the oil sump instead.
| Part no. | Watts | Volts | Size | Type | Repl. cord |
|---|---|---|---|---|---|
| 24025 | 25 W | 120 V | 1" × 5" | Silicone pad | — |
| 24050 | 50 W | 120 V | 2" × 5" | Silicone pad | — |
Bond the pad to the flat underside of the crankcase or oil sump — cleaned, degreased bare metal, not plastic shrouding. A 25–50 W pad is correct for the 0.5–1.1 L of oil in a typical portable; more wattage risks cooking the oil in such a small sump. Plug in 30–60 minutes before you need the machine, or leave it on a thermostatic outdoor timer during outage season.
Air-cooled standby generators (Generac, Kohler, Champion home units)
Use the manufacturer's cold-weather kit — it's sized and warrantied for the unit.
Generac, Kohler and Champion all sell cold-weather kits for their air-cooled standby lines, matched to the unit's kW tier. The kits pair a thermostatically controlled battery warmer with a crankcase oil heater, switching on automatically below about 0°C. Generac recommends the kit for any install where temperatures drop below -18°C — which is every province in Canada. Order by your generator's kW rating and serial number from the dealer or the manufacturer's parts site.
Liquid-cooled diesel gensets (Perkins, Kubota, Yanmar, Isuzu powered)
Larger standby and prime-power gensets use the same compact diesels as tractors and skid steers, and take real frost-plug or threaded immersion heaters — most ship with one from the factory (look for a cord near the control panel). If yours didn't, identify the engine (not the genset brand) from the engine data plate and match it in the application guides: Kubota and Yanmar listings are on our tractor and skid-steer pages.
The battery matters more than the oil
Below -20°C a lead-acid battery delivers roughly a third of its rated cranking amps, and a generator battery that sat unused since October delivers less still. If you do only one thing, keep the battery warm and charged: a battery blanket plus a float charger costs less than one service call. Standby units already float-charge their battery from utility power; the cold-weather kit adds the warmth.
For pull-start portables, the battery problem becomes a shoulder problem — thick oil can double the pull force. A pad heater fixes the oil, and 5W-30 or 0W-30 synthetic (check your manual — most air-cooled engines approve it below 5°C) fixes the rest.
Storage beats heat
A portable generator stored in an attached garage at 10°C needs no heater at all — it starts like it's September. The pad-heater play is for machines that live in an unheated shed or outside under a cover. If an outage hits and the machine is cold-soaked, bring it somewhere warmer for an hour if you can; if not, a pad heater powered from the house (while the grid is still up, before a forecast storm) is exactly what pre-storm prep looks like.
FAQ
Do generators have block heaters?
Liquid-cooled diesel gensets usually do — factory-fitted immersion heaters, same as a tractor. Air-cooled units (all portables and most home standby generators) have no coolant to heat; the equivalents are a crankcase oil heater and a battery warmer, sold together as a cold-weather kit on standby units.
Does a Generac need a cold weather kit in Canada?
Yes. Generac recommends the cold-weather kit below -18°C, a threshold every Canadian province crosses. The kit's battery warmer and oil heater switch on thermostatically, so it costs almost nothing to run in mild weather.
Can I put a pad heater on a portable generator?
Yes — a 25–50 W silicone pad (Kat's 24025 or 24050) on the bare metal of the sump is the standard retrofit. Keep it small: a portable holds about a litre of oil, and the guide rule is roughly 10 watts per quart.
Why won't my generator start in the cold?
In order of likelihood: weak or frozen battery, oil too thick for the cranking speed, stale fuel or an ungreased choke on carbureted units. Warm battery + winter-grade synthetic oil + fresh stabilized fuel solves nearly all of it.
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