The JAB DUC 2 Hi-Flo 400 Litre Direct Unvented Cylinder is a large-capacity cylinder for light commercial sites and large homes with multiple bathrooms, where sustained draw-off would exhaust a standard domestic cylinder. It is a high-recovery, mains-pressure hot water storage cylinder manufactured from Duplex stainless-steel for superior corrosion resistance, and is designed for light commercial and high-demand applications.
Heat comes from four factory-fitted 3kW titanium immersion heaters, giving fast reheat and the durability to cope with high-use commercial duty. A 28mm inlet with 1" hot and cold connections delivers high flow rates at mains pressure, while the external expansion vessel design, factory-fitted temperature and pressure relief valve and full unvented kit mean everything needed for a compliant installation arrives in the box.
4 x 3kW
Titanium immersions
1"
Hot & cold connections
7 bar / 90°C
Factory-fitted T&P valve
1600 x 660mm
Height x diameter
Important Safety Information
This is an unvented hot water cylinder and must be installed, commissioned and notified to Building Control by a G3-qualified installer in line with Building Regulations Part G3, with the Benchmark checklist completed. The immersion heater circuits must be designed and installed by a competent electrician in accordance with BS 7671 and Part P; with four 3kW elements fitted, the property's supply capacity must be assessed before installation.
Please Note
This is a direct (electric-only) cylinder with no heat exchanger coil, so it cannot be connected to a boiler, heat pump or solar thermal primary circuit. The manufacturer lists a 28mm inlet with 1" hot and cold connections alongside 22mm 316L stainless-steel compression fittings; confirm the connection arrangement against the supplied kit when planning pipework.
Good to Know
The quoted 1600mm x 660mm dimensions are for the cylinder itself. The remote expansion vessel is supplied with a factory-fitted wall mounting bracket and is mounted separately, so allow wall space close to the cylinder as well as service access to the immersion heaters and controls.
Key Features
Duplex stainless-steel vessel
The inner container is made from Duplex stainless-steel for superior corrosion resistance, backed by a lifetime manufacturing warranty on the inner container.
4 x 3kW titanium immersions
Four factory-fitted 3kW titanium immersion heaters provide fast reheat and are built to cope with the high use demands of commercial applications.
High flow at mains pressure
A 28mm inlet with 1" hot and cold connections supplies mains pressure hot water at high flow rates to multiple outlets simultaneously.
316L stainless fittings
316L grade stainless-steel 22mm compression fittings match the corrosion resistance of the vessel for a long-lasting installation.
Factory-fitted safety
A temperature and pressure relief valve set at 7 bar / 90°C is fitted at the factory, and a full unvented kit is supplied.
External expansion design
The remote expansion vessel comes with a factory-fitted wall mounting bracket, and the cylinder is fully insulated to minimise heat loss.
Technical Specifications
General
Range
JAB DUC 2 Hi-Flo (external expansion)
Cylinder type
Direct unvented, high recovery
Storage capacity
400 litres
Application
Light commercial and high-demand domestic
Country of manufacture
United Kingdom
Construction
Vessel material
Duplex stainless-steel
Fittings
316L grade stainless-steel 22mm compression
Insulation
Fully insulated
Connections
Hot & cold connections
1"
Heat exchanger coil
None (direct electric)
Heating
Immersion heaters
4 x 3kW titanium, factory-fitted
Combined immersion rating
12kW (all four elements)
Safety & Kit
T&P relief valve
Factory-fitted, 7 bar / 90°C
Expansion vessel
Remote, with factory-fitted wall mounting bracket
Unvented kit
Full kit supplied
Warranty
Inner container
Lifetime manufacturing warranty (manufacturer terms apply)
Frequently Asked Questions
What does “direct” mean on this cylinder?
A direct cylinder is heated entirely by its own electric immersion heaters; it has no internal coil for a boiler or heat pump. This model uses four 3kW titanium immersions, making it well suited to sites where electricity is the only practical heat source for hot water.
Can all four immersion heaters run at the same time?
The four elements have a combined rating of 12kW when all are energised. Whether they are wired to run together, in stages or on different schedules depends on the electrical design of the installation, which must be carried out by a competent electrician to BS 7671 after assessing the available supply.
Who can install this cylinder?
Because it is an unvented cylinder, installation, commissioning and Building Control notification must be carried out by a G3-qualified installer under Building Regulations Part G3, including correct tundish and discharge pipework and completion of the Benchmark checklist.
What is included in the box?
The 400L cylinder is supplied with four factory-fitted 3kW titanium immersion heaters, a factory-fitted T&P relief valve (7 bar / 90°C), a remote expansion vessel with factory-fitted wall mounting bracket and a full unvented kit.
How much space does the 400L model need?
The cylinder measures 1600mm high x 660mm in diameter. Allow additional wall space nearby for the remote expansion vessel, clearance to service the immersion heaters and valves, and a floor able to take the load when full — the stored water alone weighs around 400kg.
What warranty is provided?
JAB provides a lifetime manufacturing warranty on the inner container and 2 years on components, subject to the manufacturer's terms and conditions.
