| Combustion Chamber | Fuel is mixed with combustion air and burned inside a sealed chamber. The released heat is transferred through a heat exchanger. | Combustion is separated from the air supplied to the passenger compartment or sleeping area. | Flame failure, incomplete combustion, or damage to the chamber can create hazardous combustion products. | Use a controlled fuel supply, flame monitoring, correct combustion-air routing, and automatic shutdown after an abnormal condition. | Safety design and installation provisions are relevant to type approval under UNECE Regulation No. 122. |
| Heat Exchanger | Transfers heat from combustion gases to the clean air stream while keeping the two air paths physically separate. | Heat transfer occurs across a metal wall; combustion gases should remain in the exhaust circuit. | A crack, corrosion, or seal failure could allow carbon monoxide or other exhaust gases to enter the heated-air stream. | Inspect the exchanger, seals, and air passages. Replace damaged components and prevent unauthorized modifications. | Maintaining separation between combustion products and heated air is a fundamental safety principle for vehicle heating systems. |
| Combustion-Air Intake | Supplies oxygen to the burner from outside the heated cabin or from an approved location specified by the installation design. | The intake should be protected from exhaust recirculation, water ingress, road debris, and blockage. | Restricted or contaminated intake air can cause poor combustion, overheating, smoke, or increased carbon monoxide production. | Keep the intake unobstructed and separated from the exhaust outlet. Do not place it where cabin or engine exhaust can be drawn in. | Correct routing and protection support the installation and operational safety requirements associated with UNECE Regulation No. 122. |
| Exhaust Pipe | Carries combustion gases from the heater to the exterior of the vehicle or enclosure. | The outlet must discharge outside and should not terminate near doors, windows, ventilation intakes, or sleeping-air inlets. | Exhaust leakage or recirculation can expose occupants to carbon monoxide and other combustion products. | Use heat-resistant routing, secure fasteners, suitable clearances from combustible materials, and regular leak inspections. | Exhaust routing, outlet position, and protection from occupant exposure are important installation considerations under ECE R122-based approval. |
| Fuel Metering and Pump | A metering pump supplies a controlled quantity of fuel to match the heater’s selected output level. | Fuel delivery is normally pulsed or electronically controlled rather than supplied continuously at full flow. | Fuel leakage, incorrect fuel delivery, or poor connections can cause fire, smoke, or unstable combustion. | Use approved fuel lines and connections, protect them from heat and abrasion, and shut down the fuel supply when a fault is detected. | Fuel-system integrity and protection against fire are central to vehicle-heater safety requirements. |
| Glow Ignition Device | Heats the combustion zone to ignite the fuel-air mixture during the start-up sequence. | Ignition is normally active only during start-up or controlled restart phases. | Repeated failed ignition can leave unburned fuel in the chamber, causing smoke or delayed ignition. | Use ignition-failure detection, purge or cool-down logic, and a lockout or fault state after repeated unsuccessful attempts. | Automatic fault handling supports the safe-operation expectations of ECE R122 approval. |
| Air-Circulation Blower | Draws cabin or room air across the heat exchanger and distributes the warmed air through ducts or outlets. | Some systems use one blower for heated air and a separate path for combustion air. | Blocked outlets, a failed blower, or restricted ducts can cause excessive internal temperature. | Monitor blower operation where applicable, keep outlets clear, and provide automatic shutdown or reduced output when airflow is inadequate. | Airflow management contributes to overheat prevention and safe operation. |
| Temperature Sensor | Measures outlet, internal, cabin, or coolant-related temperature so the controller can regulate heat output. | Control commonly uses staged output, modulation, or cycling rather than continuous maximum heating. | A failed or inaccurate sensor can cause overheating, insufficient heating, or incorrect shutdown behavior. | Use plausibility checks, fault detection, and a safe shutdown strategy when sensor readings are missing or outside the expected range. | Monitoring and protective control functions support the safety assessment required for approved heating installations. |
| Overheat Protection | Stops fuel delivery or reduces heater output when internal, outlet, or component temperature exceeds a safe threshold. | Essential protective function | Blocked ducts, a failed fan, excessive ambient temperature, or restricted airflow may cause overheating and fire risk. | Provide independent or suitably reliable thermal protection, automatic fuel shutoff, fault indication, and controlled cool-down. | Overheat protection is a key safety feature for heaters evaluated under UNECE Regulation No. 122. |
| Carbon Monoxide Control | Controls CO risk primarily by maintaining a sealed combustion circuit, correct air-fuel operation, sound exhaust routing, and safe installation. | CO is colorless and odorless; smell is not a reliable warning | Exhaust leaks, poor combustion, blocked exhaust, or exhaust recirculation can expose occupants to carbon monoxide. | Install a certified CO alarm where appropriate, never operate with a known exhaust leak, and provide adequate ventilation when required by the vehicle or enclosure design. | CO prevention is addressed through heater construction, combustion separation, exhaust arrangements, and installation safety provisions. |
| Controller and Fault Logic | Coordinates start-up, fuel metering, ignition, blower speed, temperature regulation, fault detection, and shutdown. | Typical fault responses include fuel cutoff, post-purge, cool-down, restart limitation, and stored fault indication. | A control-system failure could allow unsafe fuel delivery, failed cooling, or repeated ignition attempts. | Use fail-safe states, watchdog or diagnostic functions where applicable, and prevent operation when critical faults remain active. | Control reliability and fault responses form part of the overall safety evaluation for type-approved heating equipment. |
| Electrical Protection | Supplies power to the controller, blower, ignition device, sensors, and fuel pump from the vehicle electrical system. | Electrical demand varies by heater size and is often higher during start-up and cool-down than during steady heating. | Short circuits, poor grounding, undersized wiring, or low voltage can cause overheating, malfunction, or battery depletion. | Use correctly rated fuses, protected wiring, secure terminals, suitable grounding, and low-voltage shutdown where provided. | Electrical installation must be compatible with the vehicle and the approved heater installation instructions. |
| Installation Clearances | Maintain separation between hot components, exhaust parts, fuel lines, wiring, insulation, and combustible materials. | Clearance requirements depend on heater construction, shielding, materials, and the installation instructions. | Insufficient clearance can cause heat damage, melting, fuel ignition, or fire. | Follow the approved installation layout, use heat shields when specified, and prevent contact with moving or hot vehicle parts. | Installation protection and fire prevention are important elements of compliance with ECE R122 requirements. |
| Maintenance and Inspection | Regular checks confirm that the combustion circuit, exhaust, fuel system, wiring, sensors, and air passages remain serviceable. | Inspection frequency should reflect operating hours, environment, fuel quality, and the vehicle or heater manufacturer’s instructions. | Accumulated soot, corrosion, loose connections, blocked ducts, or damaged seals can increase safety risks. | Inspect before seasonal use, test alarms where fitted, keep air passages clear, and stop operation if smoke, unusual odor, or repeated faults occur. | Continued compliance depends on preserving the approved configuration and safe operating condition. |
