The Navien NCB300-37K is a wall-hung, room-sealed gas condensing combi boiler rated at 37kW, Navien's entry model offering the same core componentry as the larger NCB500/700 ranges in a compact, cupboard-friendly design. Built around dual stainless steel heat exchangers, it combines a wide 6:1 turndown ratio with a 5-year parts and labour warranty as standard, making it well suited to two showers.
15.2 l/min
DHW Flow (ΔT35°C)
5 yrs
Parts & Labour Warranty
Gas Safe Registration Required
Installation, commissioning and servicing of this boiler must be carried out by a Gas Safe registered engineer. A Benchmark commissioning checklist must be completed and left with the end user, and the flue must be positioned in accordance with the clearances set out in the manufacturer's installation and operation manual.
LPG Conversion
The boiler is shipped ready to fire on natural gas. An LPG conversion kit is included in the boiler packaging for field conversion by a suitably qualified Gas Safe engineer, but is not fitted as standard.
Why This Boiler
Dual Stainless Steel Heat Exchangers
Both the primary and secondary heat exchangers are stainless steel rather than aluminium, giving strong resistance to corrosion from acidic condensate over the boiler's working life.
6:1 Turndown Ratio
A wide 6:1 modulation range lets the burner idle down to a low minimum output on milder days, avoiding the short-cycling that wears components faster on boilers with a narrower turndown.
Hydrogen-Ready (20% Blend)
The NCB300 is tested and approved for use with up to a 20% hydrogen blend in the gas supply, helping future-proof the installation.
ErP A+ with Smart Plus
Paired with a Navien Smart Plus wireless thermostat, system efficiency rises from ErP A (93%) to ErP A+ (98%), thanks to weather forecasting and geofencing.
Compact, Lightweight Design
At 395 x 285 x 680mm and 33kg lift weight, the NCB300 is built for easy cupboard-fit installation without sacrificing DHW performance.
Smartphone Compatible
Pairs with the Navien Smart Plus app for remote adjustment of heating and hot water, alongside smart weather forecasting and geofencing.
Technical Specification
| General |
| Article number |
PNCB3000037L001 (NCB300-37K) |
| Boiler type |
Wall-hung, room-sealed, fan-assisted condensing combi (B23-C13-C33-C53-C83) |
| Fuel type |
Natural gas (LPG conversion kit included, field conversion required) |
| Dimensions (W x D x H) |
395 x 285 x 680 mm |
| Guarantee |
5 years parts and labour |
| Shower rating |
Two showers |
| Heating Performance |
| Heat input range |
4.6 – 26.8 kW |
| Heat output range (80/60°C) |
4.5 – 26.0 kW |
| Modulation (max/min) |
6:1 |
| Domestic Hot Water |
| DHW heat input / output range |
4.6 – 37.0 kW |
| DHW flow rate (ΔT = 25°C) |
21.3 l/min |
| DHW flow rate (ΔT = 35°C) |
15.2 l/min |
| DHW flow rate, kitchen tap (ΔT = 45°C) |
11.8 l/min |
| DHW turndown ratio |
8:1 |
| Performance & Emissions |
| ErP efficiency |
A (93%) — A+ (98%) with Smart Plus control |
| NOx classification |
Class 6 |
| Lift weight |
33 kg |
| Flue |
| Flue diameter |
Coaxial 60/100mm |
| Max. horizontal coaxial flue length |
8 m |
| Max. vertical coaxial flue length |
8 m |
Frequently Asked Questions
Can I run this boiler on LPG?
An LPG conversion kit is included in the boiler's packaging as standard, but the boiler ships configured for natural gas. Conversion must be carried out by a Gas Safe registered engineer holding the appropriate LPG qualification.
What size property is the NCB300-37K suitable for?
With a DHW output of 37kW, the NCB300-37K is designed for two showers, subject to a proper heat loss calculation and mains flow rate check.
Does this boiler include a flue kit?
No, this listing is for the boiler only. A compatible Navien 60/100mm flue kit is required and sold separately.
Will this boiler improve its efficiency rating with a smart thermostat?
Yes. Pairing a Navien Smart Plus wireless thermostat with this boiler raises the system's ErP rating from A (93%) to A+ (98%).
Can I install this boiler myself?
No. UK law requires that all gas boiler installation, commissioning and servicing work is carried out by a Gas Safe registered engineer.
