Generator Block Heater — Coolant Preheating for Diesel & Standby Gensets
A generator block heater is an electric coolant heater that keeps a genset's engine warm while it sits idle, so it starts fast and takes load without hesitation. It does not burn fuel. It plugs into a wall outlet, warms the coolant, and circulates it through the block with a built-in pump.
Vvkb has been building engine coolant heaters in China since 1996. The Titan range covers 600W to 2,500W in 110V and 230V, with a 900 L/hr pump and dual thermostats on every pumped model.
- What it does: holds coolant between 113°F and 149°F (45°C–65°C) so the engine starts on the first crank
- Power range: 600W–2,500W, 110V or 230V single-phase (3,000W by custom order)
- Plug-in time: 2–3 hours before start for most gensets — not all night
- Port size: 5/8" (16mm) standard, 3/4" and 1" available at order
- Fits: liquid-cooled gensets only — see the fit check below before you buy
- Certified: CE & RoHS certified, tested to IEC 60335-1 by TÜV Rheinland
Why Heaters Are Fitted to a Generator
Heaters are fitted to a generator so the engine can accept electrical load the moment it starts, instead of stumbling through a cold crank. On a cold engine, oil is thick, clearances are tight, and the first few seconds decide whether the transfer happens on time.
The margin is tighter than most people assume. Under NFPA 110, a Level 1 emergency power system has 10 seconds from utility failure to load acceptance. The automatic transfer switch alone eats 1–3 seconds of that window.
Four things a generator heater buys you:
- Load acceptance. A warm engine reaches rated speed and voltage in seconds, not after a long crank and warm-up.
- Less cold-start wear. The majority of engine wear happens in the first few seconds of a cold start, before oil reaches the top end.
- Less condensation and wet stacking. A diesel genset that starts cold and runs light builds unburnt fuel and moisture in the exhaust. Starting warm reduces both.
- Cleaner cold starts. A preheated engine produces noticeably less white smoke, hydrocarbons and CO on start-up.
In cold regions this is not optional equipment. It is the difference between a generator that carries the building and a generator that logs a failed start.
What a Generator Block Heater Actually Is
A generator block heater is an electric resistance heater plumbed into the engine's coolant circuit. Current heats an element, the element heats the coolant, and a small pump pushes that warm coolant through the engine block. There is no flame, no fuel line and no exhaust.
The naming is a mess across the industry, and every one of these terms means the same device:
- Generator block heater / block heater for generator — the common North American term
- Generator coolant heater / engine block heater for generator — what the spec sheet usually says
- Jacket water heater / generator jacket heater — standard wording on larger diesel sets
- Genset block heater / generator engine heater — dealer and OEM shorthand
What it is not: a generator block heater does not heat a room, and it is not a fuel-fired heater. If you searched for a way to run a heater from a generator, that is a different product entirely. Everything on this page is about warming the generator's own engine.
Four Types You Will Run Into
| Type | How it mounts | Suits |
|---|---|---|
| Inline circulating heater (Vvkb Titan) | Cut into a coolant hose, own pump moves the coolant | Any liquid-cooled genset; the only type that heats the whole block evenly |
| Freeze plug / frost plug heater | Replaces a core plug in the block | OEM fit; seizes in place after a few years and can be brutal to remove |
| Tank-style heater | External tank in the coolant loop, thermosiphon | Larger sets, no moving parts, slower to warm |
| Radiator hose heater | Spliced into a hose, no pump | Small engines; heat stays near the heater without circulation |
What Is Actually Inside a Generator Cold Weather Kit
An OEM generator cold weather kit is usually two or three separate heaters bundled together, and only one of them decides whether your engine starts. Understanding the split saves you money and stops you buying the wrong part.
| Component | What it does | Does it matter? |
|---|---|---|
| Block / coolant heater | Warms engine coolant, typically 100–130°F (38–54°C) | Yes. This is the part that changes cranking |
| Oil filter or crankcase heater | ~50W cuff on the filter, warms oil in air-cooled sets | Useful on air-cooled units that have no coolant |
| Battery warmer / pad | Heats the battery to hold cranking amps | Contested — see below |
| Breather / carburetor heater | Prevents icing on gas and NG units | Only on specific gas models |
Technicians on the Generac owner forums are consistent on one point: fit the coolant or oil heater, and treat the battery pad as optional. Installers report battery pads shorting out over time under the weight of the battery, and a battery on a maintainer usually solves the same problem.
Common reference kits and parts people search for include Generac's 084918C block heater and cold weather kits such as 5616, and Kohler's GM90235-KP1-QS. A Vvkb Titan replaces the coolant heater portion of those kits. It does not replace the battery or breather warmers.
The mistake that causes most returns: air-cooled home standby generators — most Generac and Kohler units in the 9kW–22kW class — have no coolant at all. No coolant heater of any brand can fit them, and kits sold for the liquid-cooled line will not work on the air-cooled line. Check your unit before ordering. If there is no radiator and no coolant hose, you need an oil heater, not a block heater.
Does a Titan Fit Your Generator? Read This First
The Titan range is single-phase, 2,500W maximum, and designed as an intermittent preheater — you plug it in a few hours before start. That defines exactly where it belongs and where it does not.
✅ Good fit
- Liquid-cooled diesel gensets on farms, workshops, remote properties and vacation bases
- Portable and towable diesel generator sets
- Liquid-cooled standby units (Generac Protector class, Kohler liquid-cooled and similar)
- Construction equipment and light plant with a coolant circuit
- Marine auxiliary gensets
- Anywhere you have a 110V or 230V single-phase outlet near the set
❌ Wrong tool — buy something else
- Air-cooled gensets. No coolant, nothing to heat.
- NFPA 110 Level 1 life-safety systems and NFPA 20 diesel fire pumps. Those specs call for coolant held continuously inside a defined band — NFPA 20 requires 120–140°F (49–60°C). The Titan cycles between 113°F and 149°F (45°C–65°C) and is built for intermittent preheating, so it is not the right product for a code-inspected life-safety installation.
- Hazardous or classified areas (oil and gas, Class I Div 1/2, Zone 1/2). Vvkb holds no ATEX, IECEx or UL Class I approval. We will tell you that directly rather than sell around it.
- Large industrial sets on 400V/415V three-phase needing 6kW and up. That is a different class of hardware.
If your project falls in the second list, we would rather say so now than have you specify the wrong part. For everything in the first list, keep reading.
Sizing: Which Titan for Your Genset
Size a generator block heater by coolant volume and engine displacement, not by generator kW output. A 20kW set with a 3.0L engine needs more heat than a 20kW set with a 1.8L engine, because there is more metal and more coolant to bring up.
| Genset / engine | Model | Wattage | Plug-in before start |
|---|---|---|---|
| Small portable set, under 1.5L | Titan-B1 or Titan-P1 | 1,000W–1,200W | 30–60 minutes |
| Liquid-cooled standby, 1.5L–3.0L | Titan-P3 | 1,500W | 60 minutes–2 hours |
| Diesel genset, 3.0L–6.0L | Titan-P3 or Titan-P4 | 1,500W–2,000W | 2 hours |
| Larger diesel set, 6.0L and up | Titan-P5 | 2,000W–2,500W | 2–3 hours |
| No pump wanted / thermosiphon layout | Titan-P6 | 600W–2,000W | 3 hours |
North American 110V limit: a standard 15A household circuit tops out around 1,500W in continuous use. On 110V, order 1,000W or 1,500W. The 2,000W and 2,500W ratings are for 230V.
Titan Models for Generators — Full Comparison
Every pumped Titan uses the same 900 L/hr circulation pump and the same thermostat settings. What changes is wattage, heating element construction and port geometry.
| Model | Power | Pump | Thermostats | Heating element | Best for |
|---|---|---|---|---|---|
| Titan-P5 | 1,000–2,500W | 900 L/hr | Dual ceramic | Copper-plated tube | Diesel gensets, heavy equipment, large trucks |
| Titan-P4 | 1,000–2,500W (230V) 1,000–1,500W (110V) | 900 L/hr | Dual ceramic | Steel tube die-cast into aluminium | Large sets; straight 180° ports for easy hose runs |
| Titan-P3 | 1,000–2,500W | 900 L/hr | Dual ceramic | Steel tube die-cast into aluminium | Mid-size gensets; 90° ports suit tight bays |
| Titan-P6 | 600–2,000W | None — thermosiphon | Single, 65°C/45°C | Stainless steel tube | Simple installs; every part user-replaceable |
| Titan-B1 | 1,200W standard | 900 L/hr | Dual ceramic | Steel tube die-cast into aluminium | Small sets and extreme cold |
| Titan-P1 | 500–2,000W | 900 L/hr | Dual | Copper-plated tube | Small portable sets and light engines |
All models take 5/8" (16mm) hose connections as standard. 3/4" and 1" couplers are available, but they are selected at the time of order and are not supplied in the box by default.
Jacket Water Heaters for Large Diesel Gensets
On larger diesel sets the same device is called a jacket water heater, and the sizing logic shifts from "warm it before start" to "hold it warm continuously". That distinction matters more than the name.
A true jacket water heater on a large standby set runs year-round, holding coolant near 100–130°F (38–54°C) so the engine is always seconds from full load. Those units are typically three-phase, 400V/415V, and 6kW and up, with duty cycles measured in years of continuous operation.
Vvkb's range stops below that. The Titan-P5 tops out at 2,500W standard (3,000W by custom order) on single-phase supply, with a pump rated to 5,000 hours and a heating element rated to 8,000 hours. That is sized for intermittent preheating of small and mid-size sets.
If you are specifying a water jacket heater for generator sets above that band, or for a continuously energised installation, you need industrial hardware and we will say so. For portable, agricultural, marine and light commercial gensets, the Titan is the right size of tool.
Cummins, Kohler, Generac, Perkins and John Deere Sets
The Titan is a universal inline heater — it splices into a coolant hose rather than bolting to a specific engine casting, so it is not tied to any engine brand. What changes between brands is where the hose runs and how much coolant you are heating.
- Cummins — the most common request we get for generator coolant heaters. Mid-range B and QSB series sets take a P3 or P5 comfortably. Large KTA-class engines are outside our range.
- Kohler — liquid-cooled models accept an inline heater in place of the OEM kit. Air-cooled models do not, as above.
- Generac — Protector and other liquid-cooled units are a fit. The 9kW–22kW air-cooled home standby line is not.
- Perkins — widely used on towable and rental sets; a P3 or P5 handles most of the range.
- John Deere and Kubota — common on agricultural and compact gensets. Both accept a P3 in the usual displacements.
Because the heater goes into the hose, you are not hunting for a part number that matches a casting. You are matching wattage to coolant volume and port size to hose diameter.
How It Works, and Why It Cycles Instead of Running All Winter
The Titan heats coolant to 149°F (65°C), cuts power, then restarts when coolant falls to 113°F (45°C). The built-in 900 L/hr pump circulates continuously while it is heating, so warmth reaches the whole block rather than pooling around the element.
This is a real difference from most OEM standby kits. Owners regularly report an OEM cold weather kit drawing power on a 60°F (16°C) day, because those units are designed to hold a set temperature year-round. The Titan is a preheater: it cycles, and you switch it off when you do not need it.
Why 149°F (65°C) Is More Than Enough
You do not need to reach operating temperature before starting. Most cold-start wear happens in the first 30 seconds, before oil films establish, and coolant at 86–122°F (30–50°C) already thins the oil enough to change that.
The benefit starts the moment the heater does. Every degree of coolant temperature lowers oil viscosity and improves lubrication at the instant of cranking.
Installing a Block Heater on a Generator
Mount the heater at the lowest point of the coolant circuit with the outlet pointing up, then bleed every trace of air out before you energise it. Trapped air is the single most common cause of a heater that runs hot and heats poorly.
Parallel or In Series?
Both work, and the right choice depends on engine size.
- In series (inline). The heater sits in the main coolant loop and warms everything. Simple, and correct for small engines. Titan-P1 and B1 ship for series installation and include no tee fittings.
- In parallel. Two tee fittings create a local bypass so the pump circulates only the coolant near the block. On a large engine this reaches useful temperature far faster than heating the entire loop. Titan-P3, P4, P5 and P6 ship with two tee fittings for this.
Six Rules That Decide Whether It Lasts
- Outlet up. Point the outlet upward or tilted upward so air can escape toward the engine.
- Mount low. The lowest practical point in the circuit, so coolant reaches the heater by gravity.
- Bleed all air. From the heater and both hoses. Repeat after the first heat cycle.
- Keep 4–6 inches (10–15cm) from fuel lines.
- Never run the engine while the heater is plugged in. Circulating hot coolant across a live element creates bubbles and damages the heater.
- Use distilled water in the coolant mix. Tap water leaves mineral deposits that foul the pump.
How to tell it is working: just after switch-on the body should feel only slightly warm. If it feels hot right away, there is air trapped inside — shut it off and bleed again. As the whole system warms over the following hour, the body warms too, and that is normal.
Full step-by-step detail, including torque and hose routing, is in the block heater installation and troubleshooting guide.
Certifications
Vvkb engine coolant heaters are CE and RoHS certified. The range has been tested to IEC 60335-1 by TÜV Rheinland under report 50073775 001, and holds a TÜV Rheinland EMC conformity certificate for Directive 2014/30/EU.
The heaters are Class I appliances and must be earthed. Certification covers 230V configurations at the rated powers listed on each model's specification. If you need documentation for a tender, ask and we will send the certificate numbers so you can verify them independently.
Generator Block Heater FAQ
What does a block heater do on a generator?
It keeps the engine's coolant warm while the generator sits idle, so the set starts on the first crank and accepts load immediately. An electric element heats the coolant and a built-in pump circulates it through the block. Nothing burns, and the heater runs off a normal wall outlet.
Do you leave a generator block heater plugged in all night?
No. Two to three hours before start is enough for most gensets, and small sets need only 30–60 minutes. Leaving it on overnight adds electricity cost with almost no extra benefit, because the coolant reaches the thermostat cut-out point long before morning. We do not recommend unattended overnight operation.
Do engine block heaters really work?
Yes, and the effect is audible. Owners consistently report the difference in cranking speed on sub-zero mornings. Coolant at 86–122°F (30–50°C) thins the oil enough that lubrication reaches the top end in the first seconds instead of the first minute — which is exactly when most cold-start wear happens.
At what temperature do you need a block heater on a generator?
Below about 14°F (-10°C) oil viscosity starts to slow cranking noticeably, and below -4°F (-20°C) it becomes a real starting problem. Diesel sets need it sooner than natural gas sets, because compression ignition depends on a warm cylinder. On a natural gas standby unit in a mild climate, a maintained battery matters more than a block heater.
Why does my cold weather kit run even on a 60°F day?
Because most OEM standby kits are designed to hold coolant at a fixed temperature year-round, not to preheat before a start. That is normal behaviour for a factory jacket water heater on a life-safety set, and it is why owners see them energised in mild weather. A Vvkb Titan works differently — it cuts out at 149°F (65°C), restarts at 113°F (45°C), and you switch it off when the cold snap passes.
Will a coolant heater fit my air-cooled Generac or Kohler standby generator?
No. Air-cooled home standby units — most models in the 9kW to 22kW class — have no coolant circuit at all, so no coolant heater of any brand can be fitted. Those units use an oil-filter or crankcase heater instead. Only liquid-cooled sets, such as the Generac Protector class and Kohler's liquid-cooled range, accept an inline coolant heater. Check for a radiator and coolant hoses before ordering.
Do block heaters have a thermostat?
Yes on every Vvkb Titan. The pumped models carry dual thermostats — a control thermostat plus a second one as backup — set to cut out at 149°F (65°C) and restart at 113°F (45°C). The B1, P3, P4, P5 and P6 use ceramic thermostats. There is no adjustable or high-temperature version; 65°C is the only cut-out we build.
Can I use a Titan on an NFPA 110 emergency generator or a diesel fire pump?
No, and we would rather tell you now. NFPA 20 requires the jacket water held continuously at 120–140°F (49–60°C), and NFPA 110 Level 1 systems call for continuous temperature maintenance. The Titan cycles down to 113°F (45°C) and is built for intermittent preheating, so it does not meet those specifications. Code-inspected life-safety installations need a purpose-built industrial jacket water heater.
What actually makes a generator block heater fail?
Almost every failure traces back to installation, not to running hours. Air trapped in the heater or hoses stops the coolant carrying heat away, so the unit runs hot, the pump cycles on and off, and performance drops. Mount the heater at the lowest point with the outlet upward, bleed the circuit thoroughly, bleed it again after the first heat cycle, and keep the coolant topped up. Get that right and these heaters run for years without attention.
Should I buy the block heater or the battery warmer?
The coolant heater, if you only buy one. Generator technicians on owner forums say the same thing repeatedly: fit the oil or coolant heater and treat the battery pad as optional, since a battery on a maintainer solves the same problem without a heating pad under it. Vvkb makes the coolant heater only — we do not sell battery warmers.
How much electricity does a generator block heater use?
A 1,500W heater draws about 1.5 kWh per hour while the element is energised, but the thermostat cuts power once coolant reaches 149°F (65°C), so real consumption over a 2-hour preheat is well below 3 kWh. On a typical North American tariff that is a few cents per start. Note that a 110V 15A household circuit tops out around 1,500W continuous.
Can I fit a block heater to a portable generator?
Yes, if it is liquid-cooled. Towable and larger portable diesel sets have a coolant circuit and take a Titan-P3 or P5 without modification. Small air-cooled portable generators do not. The heater splices into a coolant hose, so you need a hose of 5/8" (16mm) or a size we can supply couplers for, and a 110V or 230V outlet within reach of the set.
Specifying Heaters for Your Gensets?
Vvkb has manufactured engine coolant heaters since 1996, and supplies genset assemblers, dealers and fleet operators across Europe, North America and the Middle East. Tell us the engine displacement, coolant capacity, supply voltage and annual quantity, and we will come back with the right model rather than the biggest one.
Buying one or two for your own set? Order direct from our retail store — no minimum, ships from stock.
REQUEST A QUOTE BUY THE TITAN-P5 →Pick by Application
- Diesel genset, 6.0L and up? → Titan-P5 inline block heater
- Mid-size genset, tight engine bay? → Titan-P3 with 90° ports
- Large set, straight hose run? → Titan-P4 inline heater
- No pump wanted? → Titan-P6 thermosiphon heater
- Small portable set? → Titan-B1 compact heater
Related Guides
- Engine block heater buying guide: types, sizing and installation — the full comparison of block heater types across all vehicles and engines
- Vvkb engine block heaters — the complete Titan range with specifications for every model
- Tractor block heaters — same technology sized for agricultural engines
