Why Diesel vs. Other Heat Sources
A 2kW sealed forced-air heater is the standard heating solution for the Tune M1. The two most popular options are the Truma Varioheat (a propane/LPG unit available as a Tune factory install for ~$3,600–$4,000) and Chinese-made diesel heaters from VEVOR or HCALORY ($100–$200 for a DIY install). Both share the property that matters: combustion happens in a sealed chamber and exhaust vents outside the cabin — no CO risk inside, no combustion moisture added to interior air, and minimal battery draw. The Truma is included on this page despite running on propane because it behaves like a diesel forced-air heater for cabin air quality and condensation, which is what separates it from unvented Buddy-style propane heaters. Why these forced-air units dominate over other heat sources:
- Safety: Diesel combustion happens externally. No open flame inside, no oxygen consumption, no CO risk from the heat source itself (unlike propane).
- Fuel efficiency: A 2kW unit burns a fraction of a liter per hour. A small fuel supply lasts multiple nights.
- Low power draw: After startup, diesel heaters draw minimal electricity, much less than an electric heater. Your battery handles it easily.
- The units themselves are compact enough to mount under a sleeping platform or in a corner of the truck bed without eating into your living space.
The exception: if you already own propane gear and mostly camp in mild weather, propane works for occasional heat. Cold-weather regulars should start with diesel.
Sizing: How Many kW?
The M1's sleeping space is compact. You're heating a small volume of air, not a house. A 2kW unit is what most M1 owners run and it's more than sufficient for the M1's interior. Going larger adds weight and cost without meaningful benefit for this application.
The M1 warms up quickly, the small interior volume means a 2kW heater can bring the space from freezing to comfortable in 10–15 minutes. Most owners run it at 30–50% power for overnight heating once the space is up to temp. M1 owners have camped comfortably in single-digit °F temperatures with a 2kW heater, though at those extremes the heater runs at higher settings and fuel consumption increases. A Maxxair vent on low speed helps circulate the warm air evenly through the space.
Installation in the M1
The heater unit is typically mounted in the truck bed, often under the sleeping platform or at the foot of the sleeping area. Common installation approach:
- Heater body: mount to the truck bed floor or a 80/20 T-track platform. Keep it accessible for maintenance.
- Combustion air intake: route through the floor or side wall of the truck bed to outside air. The intake must be protected from water intrusion.
- Exhaust outlet: route through the floor or side wall and position away from any openings where exhaust could re-enter. Point downward or sideways, never toward any opening in the camper.
- Fuel line: run from your fuel tank (auxiliary or truck's diesel tank) to the heater's fuel pump. Chinese units include a fuel pump; premium units often do too.
- Wiring: connect to your 12V house battery. Most units include a wiring harness. Use an inline fuse.
Heater Ports: Clean Sidewall Pass-Through
One of the biggest quality-of-life upgrades for M1 diesel heater installs is a dedicated heater port, a purpose-built fitting that creates a clean, weatherproof opening through the M1's side wall for the combustion air intake and exhaust lines. Without one, owners typically route hoses through improvised holes, which can look rough and let in drafts.
Two products dominate this category in the M1 community:
DIY pass-through (no dedicated port)
Some owners skip the dedicated port products and route hoses through a weatherproof grommet or a custom-cut hole sealed with Sikaflex or butyl tape. Results vary, it works, but the fit and finish is typically not as clean and the weatherproofing requires more care. If you're cost-sensitive or the above products are out of stock, this is viable, but the dedicated ports are popular for good reason.
Fuel Source Options
Diesel heaters can draw from two fuel sources:
- Truck's diesel tank (diesel-engine trucks only): If you have a diesel truck, you can tap a T-fitting into the factory fuel line to supply the heater. This is convenient (you never need to refill a separate tank) but requires more involved installation. Note: the vast majority of M1 trucks are gasoline engines (Tacoma, Tundra, F-150, Ram 1500, Silverado all have common gas variants), so this applies to a minority of M1 owners.
- Dedicated auxiliary fuel tank: The most common approach for gas-truck owners. A 1–2L fuel bottle (like a Rotopax 1.75gal fuel pack) filled with diesel works for a weekend trip. Some owners mount a small 1-gallon tank inside the camper in a ventilated box. Diesel is available at most gas stations. Easy to refill, easy to monitor.
Diesel heaters run on standard diesel (also compatible with heating oil and red diesel in most states). Some owners have used kerosene with success, though manufacturers typically recommend against it for warranty purposes.
Power Draw & Battery Impact
Diesel heaters have two power phases:
- Startup: Brief high-draw period while the glow plug heats up, typically 10–15A for 30–60 seconds
- Running: Very low draw, typically 10–30W (0.8–2.5A at 12V) while maintaining heat
For overnight use, a 100Ah LiFePO4 battery handles a diesel heater easily. An 8-hour night running the heater at medium setting draws roughly 10–20 Ah total, well within even a modest battery setup. The startup spike (10–15A for ~60 seconds) is brief and doesn't represent a meaningful load on any properly sized battery.