VELIT 4000P Pro Diesel Air Heater - 14000BTU 4000W - 12V

The VELIT 4000P Pro is a 12V diesel air heater with VELIT’s Lambda AFR combustion monitor included. Official heating capacity is 5600–14000 BTU (4000W heat output). It is the same 4000P diesel heater as the Standard model, with the Lambda AFR in the box.

Lambda AFR is an oxygen sensor and display that read the heater’s exhaust and show how well it is burning. Lower readings mean rich (too much fuel) and higher readings mean lean (too much air). On a compatible VELIT heater with 6.X firmware, the included heater harness connects to the heater’s Auxiliary Port so the heater can correct its own fueling. The sensor powers on automatically when the heater starts, and the thermostat periodically shows live lambda values while the heater runs.

See also the VELIT 4000P Diesel Air Heater (Standard).

Key Features

• VELIT Lambda AFR included: Real-time lambda monitoring and rich/lean diagnosis from the exhaust. It can also be used for installation checks, pre-season health checks, and maintenance diagnosis, and as a standalone monitor with the included 12V cigarette-lighter harness.
• 6.X firmware and Auxiliary Port required: Closed-loop AFR control, automatic altitude compensation, Smart Priming, and Smart Ignition require a compatible VELIT heater with 6.X firmware. The included heater harness connects to the heater’s Auxiliary Port.
• Closed-loop AFR control: With 6.X firmware, the heater continuously adjusts fueling for stable, clean combustion. VELIT lists improved efficiency and stability, reduced carbon buildup, and longer service intervals among the benefits.
• Automatic altitude compensation: With 6.X firmware, the heater adapts to changing combustion conditions at elevation. The 4000P already adjusts the air-fuel mix from barometer data; the sensor adds a measured check on top.
• Smart Priming: With 6.X firmware, in Prime Mode the heater watches combustion through the sensor and stops priming once ignition is detected, which helps prevent unnecessary fuel buildup and reduces the risk of over-fueling.
• Smart Ignition: With 6.X firmware, during startup the heater monitors combustion and adjusts fueling to help it light. VELIT lists faster, more reliable starts, better cold-weather performance, fewer ignition failures, and better tolerance of a partly lost prime.
• Diesel lambda target: 1.1–1.6. Too rich can mean carbon buildup, soot, black smoke, and shorter service intervals; too lean can mean unstable combustion, hard starting, and flameout risk. Wait at least five minutes after starting the heater or changing its power setting before reading it.
• Smart thermostat included: VELIT states that a smart thermostat now comes standard.
• Built-in safety shutoff sensors: Equipped with built-in carbon monoxide and flammable gas sensors, the heater automatically shuts off in case of a leak or dangerous gas accumulation.
• High-elevation performance: Tested in Colorado at 11,000 ft +, the heater adjusts the air-fuel mix ratio based on elevation data from its barometer.
• Bluetooth connectivity: Control the heater from up to 100 feet away using a smartphone.
• Proprietary combustion chamber: Combined with a high-volume fuel pump, as described by VELIT, to support heater output.
• Complete installation kit: VELIT states the kit includes everything needed for installation, including the auxiliary fuel port connector for Sprinter, Transit, and ProMaster vans, plus a cleaning straw.
• Durable components: VELIT specifies a Japanese glow plug and a weather-sealed controller.
• Warranty: Two-year limited warranty.
• Not a carbon monoxide alarm: Lambda AFR reads combustion quality, not cabin air, and is not a replacement for a cabin carbon monoxide alarm.
• Hot sensor: The adapter and sensor get extremely hot in use. Allow them to cool before handling. The sensor has an internal heating element and should not be run in free air for more than 30 minutes.
• Proper installation still matters: The adaptive system can partly compensate for installation-related issues, but it does not replace proper fuel, intake, and exhaust installation.

Specifications

• Model: 4000P
• Official model option: Pro
• SKU: DIS4000Lam
• Fuel type: Diesel
• Voltage: 12V
• Heating capacity: 5600–14000 BTU (4000W heat output)
• Fuel consumption: 0.053–0.14 gal/h
• Operating power: 20–40 W
• Starting power: <120 W
• Operating temperature: −40°F to 75°F
• Operating elevation: Up to 16,000 ft
• Dimensions: 14.6 in × 5.5 in × 5.9 in
• Weight: 10 lb
• Lambda input voltage: 10–15 V DC
• Lambda display range: 0.8–2.2
• Diesel lambda target: 1.1–1.6
• VELIT Lambda integration: Auxiliary Port; 6.X firmware required for closed-loop AFR control, automatic altitude compensation, Smart Priming, and Smart Ignition
• Warranty: Two-year limited warranty

Heater specifications are from VELIT’s official heater specs page and 12V documentation. Lambda specifications are from VELIT’s Lambda AFR documentation.

What's Included

The Pro includes the official 4000P installation kit, plus VELIT’s Lambda AFR. The Lambda AFR includes:

• Heated oxygen sensor
• Lambda / AFR analyzer module
• Sensor adapter
• VELIT heater harness
• 12V cigarette-lighter power harness
• Rubber L-joint
• Installation hardware

The official 4000P kit includes:

• Smart thermostat: Included; VELIT states it now comes standard.
• Physical manual
• 75 mm outlet hose
• Intake hose
• Exhaust pipe
• Fuel pickup tube
• Intake filter
• Fuel pump mounting bracket
• Sealing bracket
• Air diffuser
• Mounting plate
• 16 ft fuel line
• Fuel pump connector
• Fuel filter
• 65 ml fuel pump
• Mounting clamp, outlet clamp, intake/exhaust clamp, and fuel line clamp
• Self-tapping fasteners, fuel pump bolt, mounting bolt and nut, zip ties, and fuel line connectors
• 7.89-ID3 fuel tank connector: For ProMaster
• 6.30-ID3 fuel tank connector: For Transit and Sprinter
• Cleaning straw: Listed on VELIT’s product page