Navien LCB700 21kW RSX External Regular Oil Boiler - LCB700-21RSX

Navien LCB700 21kW RSX External Regular Oil Boiler - LCB700-21RSX The Navien LCB700-21RSX 21kW External Regular Oil Boiler is a high-efficiency condensing oil-fired heat-only boiler designed for external installation, making it an excellent option where valuable indoor space needs to be preserved. Part of Navien's advanced LCB700 Blue Flame range, the LCB700-21RSX combines efficient blue flame combustion technology, a durable stainless-steel heat exchanger, HVO compatibility and long-flue capability in a robust external boiler design. The boiler provides two-stage heating performance of 16kW / 21kW at 80/60°C, with maximum output increasing to approximately 23.0kW at 50/30°C. This makes the 21RSX particularly suitable for smaller to medium-sized properties where a regular oil boiler and stored domestic hot water system are required. Key Features Navien LCB700 Blue Flame oil boiler Model: LCB700-21RSX External Regular / Heat Only boiler Maximum nominal heating output: 21kW Two-stage 16kW / 21kW output at 80/60°C Up to 23.0kW output at 50/30°C Advanced Blue Flame combustion technology ErP A-rated as standard 93% ErP efficiency Can achieve an A+ system rating with qualifying Smart Plus controls HVO compatible Stainless-steel heat exchanger Low NOx emissions Designed specifically for external installation Built-in frost protection Text-driven integral display Displays operating and fuel consumption information 3-zone ready with Navien Smart Plus controls Flexible pipework arrangements Combined PRV / condensate drainage arrangement 60/100mm coaxial plastic flue system Maximum horizontal flue length up to 20 metres Maximum vertical flue length up to 21 metres 10-year parts and labour warranty as standard, subject to Navien terms Technical Specification Brand: Navien Range: LCB700 Model: LCB700-21RSX Product Type: External Regular Oil Boiler Boiler Type: Condensing Regular / Heat Only Boiler Installation Location: External Fuel Type: Heating Oil / Kerosene HVO Compatible: Yes Heat Input Stage 1 / Stage 2: 17kW / 22kW Heat Output at 80/60°C: 16kW / 21kW Maximum Heat Output at 50/30°C: 23.0kW ErP Energy Rating: A ErP Efficiency: 93% Potential System Rating: Up to A+ with qualifying Smart Plus configuration NOx Emissions: 57.2mg/kWh Heat Exchanger: Stainless Steel Combustion Technology: Blue Flame Flue Type: Coaxial Plastic Flue Size: 60/100mm Maximum Horizontal Flue Length: 20m Maximum Vertical Flue Length: 21m 87° / 90° Elbow Equivalent: 1.3m 45° Elbow Equivalent: 1.0m External Width: 515mm External Depth: 673mm External Height: 882mm Boiler Weight: 64kg Control: Integral text-driven display Smart Control Compatibility: Navien Smart Plus Zone Capability: Up to 3 zones with compatible Smart Plus controls Frost Protection: Built-in frost thermostat Warranty: 10-year parts and labour warranty subject to Navien terms Designed for External Installation The LCB700-21RSX is specifically designed for external installation, allowing the boiler to be located outside the property rather than occupying valuable kitchen, utility room or cupboard space. The external enclosure protects the boiler components while Navien's built-in frost protection system helps protect the appliance during cold conditions, provided the boiler remains electrically powered and installed in accordance with Navien's instructions. Built-In Frost Protection Navien boilers incorporate an automatic frost protection function. If the water temperature within the boiler falls to a sufficiently low level, the boiler and pump can operate automatically to protect the appliance from freezing. External system pipework must still be correctly insulated and protected against freezing. Additional frost protection may be required depending on the installation location and system design. Blue Flame Oil Technology The LCB700 range uses Navien's Blue Flame combustion technology to provide highly efficient oil combustion with reduced emissions. The LCB700-21RSX achieves an ErP A rating and 93% efficiency as standard while producing NOx emissions of approximately 57.2mg/kWh. Two-Stage 21kW Heating Performance The 21RSX provides two-stage heating output of approximately 16kW and 21kW at 80/60°C. At lower-temperature condensing conditions of 50/30°C, maximum useful output is approximately 23.0kW. This two-stage operation allows the boiler to respond more effectively to changing heating demand than a simple fixed-output appliance. HVO Compatible Navien identifies the LCB700 range as HVO compatible, helping provide flexibility for properties that may move towards lower-carbon liquid heating fuels. Any change of fuel type or burner setup must be undertaken in accordance with Navien's latest technical requirements by a suitably qualified oil heating engineer. Stainless-Steel Heat Exchanger A durable stainless-steel heat exchanger is used within the LCB700 range, providing resistance to the acidic condensate produced by a high-efficiency condensing oil boiler while helping maintain long-term efficiency. Flexible Flue Options The LCB700 uses a 60/100mm coaxial plastic flue system and provides unusually flexible flue routing options. Maximum horizontal equivalent length: up to 20m Maximum vertical equivalent length: up to 21m 87° / 90° elbow equivalent: approximately 1.3m 45° elbow equivalent: approximately 1.0m Actual permitted flue length depends on the complete flue arrangement and must be calculated in accordance with Navien installation instructions. Smart Plus Heating Controls The Navien LCB700 is compatible with the Navien Smart Plus control system. A correctly configured system can provide up to three heating zones, offering greater control over different areas of the property. Navien states that a qualifying Smart Plus configuration can improve the overall heating system rating from ErP A to ErP A+. Regular / Heat Only Boiler The LCB700-21RSX is a Regular / Heat Only boiler and does not produce instantaneous domestic hot water like a combination boiler. It is designed to form part of a traditional heating system incorporating the appropriate external components and, where domestic hot water is required, a separate hot water cylinder. 10-Year Warranty Navien currently supplies the LCB700 range with a 10-year parts and labour warranty as standard, subject to qualifying installation, commissioning, product registration, servicing and Navien's current warranty terms. Important Product Information This listing is for the Navien LCB700-21RSX 21kW External Regular Oil Boiler. Do not confuse the LCB700-21RSX with the internal LCB700-21RS, the external LCB700-21LSX System Boiler or the external LCB700-21LCX Combi Boiler. Flue components, hot water cylinder, system controls, oil line components, filters, valves, chemicals, pipework and other installation accessories are not included unless specifically stated elsewhere in the listing. Professional Installation Required This oil boiler must be installed and commissioned by a suitably qualified oil heating engineer. In the UK, installation by an OFTEC registered technician is recommended. The installer must confirm heat-loss requirements, boiler sizing, oil supply, fuel specification, heating system design, flue arrangement, frost protection, condensate disposal and all required controls and accessories before commissioning.