A parking heater burns 0.14–0.47 litres of your vehicle's own diesel per hour to heat the cabin with the engine off. That is one-tenth to one-twentieth of what idling costs you. It runs on 12V or 24V, needs no mains outlet, and works down to -40°F/-40°C.
We have been building vehicle heaters in China since 1996 — back when the market was Webasto, Eberspächer and a handful of others. What follows is what we would tell a friend who asked which one to buy, including the parts most sellers leave out.
Key takeaways
- Two types: air heaters warm cabin air only; coolant heaters warm the engine and the cabin through your existing vents
- Sizing: most van and truck-sleeper builds need 1,000–2,500 W, not 5KW — oversizing is the leading cause of carbon fouling
- Fuel burn: 0.136–0.252 L/hr on a 2.5KW unit, 0.201–0.475 L/hr on a 5KW unit
- Cold and altitude: rated to -40°F/-40°C, with automatic altitude compensation to 11,483 ft (3,500 m)
- Three price tiers: under $150 uncertified imports, $600–$700 manufacturer-direct, $1,000+ German dealer-installed
- Approvals are per model, not per brand — ask which certificate number covers the exact unit you are buying
What a parking heater actually is
A parking heater is a small combustion heater that runs completely independently of your engine. It draws fuel from your existing tank and burns it in a sealed chamber. Heat goes into your cabin or your coolant system while the main engine stays off.
The name comes from the use case: heating a vehicle while it is parked. You will also see them called "diesel heaters." That name took hold after 2015. Chinese manufacturers entered the market, and buyers began searching by fuel type instead of function. Both names describe the same device.
Most run on diesel because the vehicles that need them — trucks, RVs, boats — already carry it. The heater taps the existing tank, with no separate fuel supply. Gasoline versions exist for petrol vehicles.
Why truck operators buy them: the idling math
A heavy truck idling overnight burns roughly 0.8 gallons per hour; a 5KW parking heater burns about 0.13 gallons per hour on maximum output. Over a 10-hour rest period that is about 8 gallons against roughly 1.3 gallons.
At $3.80 per gallon, the difference is close to $25 a night. A driver who sleeps 200 nights a year in the cab is looking at well over 1,300 gallons. That is before counting engine hours, oil changes, and the anti-idling limits now in force across most US states and Canadian provinces.
A parking heater is not an engine block heater. A block heater plugs into a wall outlet and warms the coolant passively while parked. A parking heater burns fuel, runs on vehicle power, and heats your cabin, your coolant, or both — with no electrical hookup anywhere.
How a parking heater works
Fuel is drawn from your tank by a small metering pump and burned inside a sealed stainless-steel chamber. The heat goes either straight into cabin air or into your coolant loop. Exhaust gases leave through a separate pipe routed outside the vehicle.
Your cabin air and the combustion gases never touch. They travel through two physically separate circuits inside the heat exchanger. That separation is the whole safety argument for combustion heaters over unvented propane burners.
The whole system runs on 12V or 24V from your vehicle battery and is controlled by a thermostat, a timer or a remote. Most units reach operating temperature within 3–5 minutes of a cold start. Once the cabin hits your set point, the heater throttles down instead of switching off.
Air heater vs coolant heater: which one you need
Air heaters heat cabin air directly; coolant heaters heat your engine coolant and let your existing vehicle heater do the blowing. Get this choice right and every other decision follows from it.
| Air heater | Coolant heater | |
|---|---|---|
| What it heats | Cabin air only | Engine block plus cabin, through your existing vents |
| Warm-up time | 3–5 minutes to warm air | 20–40 minutes to warm the block |
| Install effort | Fuel line, power, exhaust, mount | The above, plus cutting into the coolant circuit and bleeding air |
| Preheats the engine | No | Yes |
| Best for | Vans, campervans, RVs, boat cabins, truck sleepers | Trucks, heavy equipment, older engines, anything started cold every morning |
| Vvkb model | Apollo-V1 2.5KW / Apollo-V2 5KW | Apollo-C1 5KW |
When the extra work of a coolant heater pays off
Cold starts do more measurable wear than hours of normal running, because oil has drained off the bearing surfaces and takes time to circulate. Preheating the coolant removes that condition entirely.
If you park overnight at -4°F (-20°C) or colder and start the engine every morning, a coolant heater is the better long-term buy. If your engine sits for weeks and you only want a warm bed, an air heater does the job. It costs less and installs in half the time.
Details on both: Apollo-V1 diesel air heater and Apollo-C1 diesel coolant heater.
What size parking heater you need
Most van, boat and truck-sleeper builds need 1,000–2,500 W of heat, which is a 2.5KW heater — not the 5KW unit almost everyone buys. The number that decides it is not the size of your vehicle. It is the insulation.
Vehicle heating has used the same K-value method for decades. Nothing here is proprietary — it is standard heat-loss arithmetic, and you can run it in two minutes.
Q = A × K × ΔT + 0.359 × V × n × ΔT Q = heat demand in watts · A = internal surface area (m²) · K = insulation factor · ΔT = temperature difference (°C) · V = internal volume (m³) · n = air changes per hour (use 1) The first term is heat lost through the walls. The second is heat lost replacing air. Surface area A is 2 × (L×W + L×H + W×H) using internal dimensions.
Pick your K value honestly
K is where people fool themselves. A camper conversion with 25mm of PIR board behind the panels is not a bare steel van with a mattress in it. That difference moves your answer by a factor of two or more.
| Build type | K value | What it looks like |
|---|---|---|
| Refrigerated body | 0.4 | Foam panel construction, thermally broken |
| Very well sealed, professional build | 0.7 | Continuous insulation, no thermal bridges |
| Well insulated and sealed | 1.5 | Insulation to walls, floor and roof; sealed gaps; window covers |
| Typical camper or RV conversion | 2.3 | Insulated, but bridges at ribs, doors and windows |
| Light insulation, unsealed | 4.0 | Thin foam or carpet lining, gaps not sealed |
| Insulated cargo body | 5.6 | Factory insulated van body, no camper detailing |
| Bare steel or aluminium body | 8.0 | No lining at all |
| Unsealed cargo box | 12.0 | Open joints, no lining. No heater wins this |
Worked examples
All figures below assume ΔT of 54°F (30°C) — that is 14°F (-10°C) outside, 68°F (20°C) inside — with one air change per hour.
| Space | Internal size | K 1.5 well insulated | K 2.3 typical | K 4.0 light insulation |
|---|---|---|---|---|
| VW T5/T6 SWB conversion | 8.5 × 5.6 × 4.6 ft | 1,000 W | 1,500 W | 2,550 W |
| Sprinter L2H2 conversion | 10.8 × 5.9 × 5.9 ft | 1,450 W | 2,200 W | 3,700 W |
| Truck sleeper cab | 6.9 × 6.9 × 6.2 ft | 1,200 W | 1,800 W | 3,050 W |
| 18 ft touring caravan | 14.8 × 6.9 × 6.6 ft | 2,200 W | 3,300 W | 5,550 W |
| 30 ft boat cabin | 13.1 × 8.2 × 5.9 ft | 2,150 W | 3,200 W | 5,400 W |
| 23 ft coachbuilt motorhome | 19.7 × 7.2 × 6.6 ft | 2,950 W | 4,350 W | 7,400 W |
Look at the first row. The same VW T6 needs 1,000 W with good insulation and 2,550 W with thin insulation — a 2.5× spread from one variable. That is why two people driving identical vans give you opposite advice. Both of them are right about their own van.
| Your calculated demand | Model | Notes |
|---|---|---|
| Up to 2,000 W | Apollo-V1 2.5KW (8,500 BTU) | Comfortable margin, runs in its efficient band |
| 2,000–2,500 W | Apollo-V1 2.5KW | Works, but you are near the ceiling on the coldest nights |
| 2,500–4,000 W | Apollo-V2, 5KW rated (4.7KW / 16,100 BTU at boost) | The correct use case for a 5KW air heater |
| Above 4,000 W | Apollo-C1 coolant heater, or two air heaters | Large motorhomes, canvas campers, workshops |
What oversizing actually costs you
An oversized heater spends its life at minimum output, and minimum output is where diesel heaters carbon up. Combustion at low flame temperature leaves soot on the glow pin and inside the heat exchanger. Do that for a season and you get error codes, weak output and smoke.
You also get the annoyances owners complain about most. The unit cycles on and off every few minutes. Fan noise goes up, and the cabin swings between hot and cold instead of holding steady.
The rule that follows from all this: if your calculation lands between two sizes, take the smaller one. A 2.5KW running at 80% output lasts longer and burns cleaner than a 5KW running at 20%. Undersizing costs you comfort on a handful of nights per year. Oversizing costs you the heater.
What to check before you buy
The market runs from $80 units on Amazon to over $1,500 for a dealer-installed German system. Four things separate them, and only one of them is visible in the listing photos.
Certifications: ask for the certificate number
A type approval covers one named model, not a whole catalogue. A brand can hold an ECE approval for one heater while the certification logo sits at the top of every product page in its range. The only way to know what you are buying is to ask which certificate number covers that exact model.
Ours, for the Apollo-V1: ECE R122 type approval E24*122R00/06*0054*00 for heating system safety, and ECE R10 E24*10R06/02*4825*00 for electromagnetic compatibility. Both were issued through NSAI in Ireland. Every Vvkb certificate number, its issuing body and the models it covers are published on the Vvkb certifications page.
What matters for your decision is the zero case. A heater with no certification has never been independently tested for combustion integrity, vibration resistance or fuel system safety. Most $80–$100 units carry nothing at all. Testing is expensive, and that is exactly where the price came from.
Power ratings: why "8KW" usually isn't
An 8KW heater that measures the same as a 5KW heater is not an 8KW heater. Output is set by combustion chamber volume, heat exchanger surface area and fan capacity. None of those change when a listing title does.
Hold the two side by side on any marketplace: identical housing, identical exhaust diameter, identical fan. Real-world output on those units rarely exceeds 5KW. It is a listing decision, not an engineering one. We wrote out the full comparison in how Vvkb heaters compare with cheap Chinese diesel heaters.
The two components that decide lifespan
The glow pin and the combustion chamber determine how many winters you get. Everything else is replaceable in an afternoon.
The glow pin ignites fuel on every single start. Most heaters use ceramic pins, but ceramic is a category, not a spec. We use Kyocera silicon nitride pins made in Japan, which hold full ignition power at -40°F/-40°C instead of fading in the cold. One pin costs over $20 at trade price — which is the entire reason budget builders fit something else.
The combustion chamber takes the full thermal load on every cycle. Ours is 2520 stainless steel, which does not deform or scale under repeated high-temperature use. Thinner, lower-grade steel warps, and a warped chamber burns incompletely — smoke, soot, then failure.
Altitude compensation, if you go up
Thin air means less oxygen, and a heater that cannot correct for it runs rich, sooty and eventually shuts down. Our controller reads barometric pressure and adjusts the fuel-to-air ratio automatically up to 11,483 ft (3,500 m).
If you camp in the Rockies, the Alps or the Andes, this is not an optional feature. Check that any heater you are considering states an altitude figure. Treat unusually high claims with the same scepticism as unusually high wattage claims.
Price: what each tier actually buys
| Tier | What you get | Who it suits |
|---|---|---|
| Under $150 | Unbranded assembly, no certification, generic glow pin, thin chamber. Works in mild conditions. | Occasional garage or shed use where failure is an inconvenience |
| $600–$700 | Certified, manufacturer-backed, Kyocera glow pin, 2520 stainless chamber, real warranty and parts supply. Apollo-V1 $629.99, Apollo-V2 $699.99. | Full-time van life, working trucks, boats, anyone depending on it |
| $1,000 and up | German engineering, dealer network, dealer installation. Excellent hardware. | Buyers who want a dealer to own the install and the warranty |
The pattern we see in support tickets is simple: people who buy cheap once usually buy twice. A $120 heater that quits at -4°F (-20°C) at a remote campsite was never the cheaper option.
Installing your parking heater
Most owners install their own heater in half a day, with no specialist tools. You need four connections: a fuel line into your existing tank, 12V or 24V power, an exhaust routed outside, and a mounting point.
Exhaust routing is where installs go wrong
Route the exhaust so gases cannot re-enter through a window, vent, or gap in the bodywork. Keep it sloping continuously downward to the outlet so condensation drains out instead of pooling in the pipe.
This single decision causes more support calls than everything else combined. Get it right and the rest of the install is mechanical work.
Give the intake room to breathe
Leave at least 8 in (20 cm) of clear space around the combustion air intake. Mounted tight against a floor panel or a wall, the heater starves and runs rich. It throws flame-out codes that look like a fault but are an installation problem.
Full sequence with torque figures, hole templates and wiring diagrams: how to install a diesel heater, step by step.
Troubleshooting quick reference
Four symptoms cover almost every support call, and three of them are fuel or air, not electronics. Work through this before contacting anyone.
| Symptom | Check first | Then check |
|---|---|---|
| Won't start | Battery voltage at the terminals during startup — you need 12.5V or better | Fuel level, air pockets or kinks in the line, pump angle, seated plugs, fuses, then intake and exhaust for blockages (mud wasps nest in both) |
| Shuts off after a few minutes | Cooling fan clogged with dust, or sharp bends restricting ducting | Air bubbles in the fuel line — bleed the system. Read the controller error code before anything else |
| Smoke or diesel smell | A few seconds of white smoke on a cold start is normal and clears | Persistent black smoke means carbon in the chamber or a restricted intake. Diesel smell means an unsealed fuel connection or exhaust re-entering the cabin |
| Weak heat | Carbon buildup from running on low for long periods | Run at full output for 30 minutes to burn off deposits. If that does not fix it, the chamber needs cleaning |
Full code list with causes and fixes: diesel heater fault codes and solutions.
Frequently asked questions
Will a 5KW heater be too big for my van?
For most van conversions under 20 ft, yes. Run the K-value calculation above — a typical Sprinter conversion lands around 2,200 W, and a T6 around 1,500 W. A 5KW unit meeting a 1,500 W demand runs at roughly 30% output, cycling on and off, sooting the glow pin as it goes. If your number is below 2,500 W, buy the 2.5KW.
My heater smoked and lost power after a few months. What happened?
Almost always carbon buildup from running on low output. Low flame temperature leaves soot on the glow pin and in the heat exchanger. That restricts airflow and makes combustion worse — a loop that ends in an error code. Run the heater at full output for 30 minutes every week or two. If it is already fouled, a full-output burn often clears it; if not, the chamber needs cleaning.
Are diesel parking heaters safe to sleep with?
Yes, when the exhaust is routed correctly. Combustion happens in a sealed chamber, and the exhaust leaves through its own pipe — cabin air and combustion gases never mix. The risk is not the heater, it is an exhaust that terminates where fumes can re-enter through a window, vent or floor gap. Fit a carbon monoxide alarm anyway; it costs $25 and removes the question.
How much fuel does a parking heater use per hour?
0.136–0.252 L/hr on the 2.5KW Apollo-V1 and 0.201–0.475 L/hr on the 5KW Apollo-V2, depending on output setting. In US terms that is roughly 8 to 28 hours per gallon. A 5-gallon jerry can runs a 2.5KW heater on medium for about four days.
Will it drain my battery overnight?
No, on a healthy battery. Startup draws around 8A at 12V for the 2–3 minutes the glow pin is preheating, then drops to 1–2A while running. Ten hours of running costs roughly 15–20Ah — under 20% of a 100Ah leisure battery. Repeated failed start attempts are what flattens batteries, and those come from fuel problems, not the heater's normal draw.
How loud is a parking heater?
About 50dB at the unit on the 2.5KW Apollo-V1 — quieter than normal conversation. Most of what people describe as noise is the fuel pump ticking, which is transmitted through the mounting bracket. Mount the pump on rubber, away from the sleeping area, and it disappears.
Does an E-mark cover every model a brand sells?
No — approvals are issued against a specific named model. This is the most common misunderstanding in the category. A brand holding an ECE R122 approval for one heater is not certified across its range, even where the badge appears on every listing. Ask for the certificate number and check which type it names. Our own numbers, model by model, are published on the certifications page.
Can I run a diesel heater in a gasoline vehicle?
Yes, using a separate diesel tank. A diesel heater cannot burn gasoline — different ignition method, different fuel system, and attempting it is a fire risk. Fit a dedicated 5–10 L diesel tank, or choose a gasoline heater that taps your existing tank instead.
Can I install one myself?
Yes, if you are comfortable drilling a floor panel and making four connections. Budget half a day for a first install. The parts that catch people out are exhaust slope, fuel pump angle and intake clearance — all covered in the installation guide. Coolant heaters are a step harder because you cut into the cooling circuit and have to bleed the air out afterwards.
Does it work at high altitude?
Up to 11,483 ft (3,500 m) with automatic compensation. The controller reads barometric pressure and leans the fuel-to-air ratio as you climb. Without that correction, a heater above roughly 5,000 ft runs rich, sooty, and eventually shuts itself down.
Ready to choose your parking heater?
We have built vehicle heaters in China since 1996. Certificate numbers are published model by model, so you can check them before you buy — not after.
- Van, campervan or boat cabin under 2,500 W? → Apollo-V1 2.5KW air heater
- Caravan, motorhome or larger cabin, 2,500–4,000 W? → Apollo-V2 5KW air heater
- Need the engine warm as well as the cabin? → Apollo-C1 coolant heater
- Buying one unit for your own vehicle? → Order on rvheater.com
Related guides
- How to install a diesel heater — the full step-by-step with templates and wiring
- Diesel heater vs propane heater — seven differences that decide which one belongs in your build
- Vvkb vs cheap Chinese diesel heaters — what the price difference buys, part by part
- Vvkb certifications — every certificate number, issuing body and the models each one covers
