The JAB DUC 2 Direct is a standard-format unvented hot water cylinder for properties where electricity is the only available heat source, with no boiler coil to plan pipework around. Available in seven capacities from 90L to 300L, it's built from duplex stainless-steel, heated by twin or triple factory-fitted immersion heaters – including a smart immersion on the 170L–300L sizes – with a remote-mounted expansion vessel.
2–3 x 3kW
Immersion (By Size)
53–175 min
Reheat Time (10°C–60°C)
7 bar / 90°C
T&P Relief Setting
Installer requirement: this is an unvented hot water cylinder and must be installed, commissioned, and notified to Building Control by a G3-qualified (Benchmark) installer in line with Building Regulations Part G3.
No boiler coil fitted: as a Direct model, the immersion heaters are the sole heat source – there is no indirect coil connection for a boiler. Immersion count and type vary by capacity (2 x 3kW on 90L–200L, 3 x 3kW on 250L–300L, with a smart immersion fitted on 170L–300L); confirm the exact configuration in the size table before ordering.
Secondary return not standard on smaller sizes: the 22mm secondary return connection is not supplied as standard on the 90L–170L models – it's only fitted as standard from 200L upwards. Confirm this against the project requirement before specifying a smaller cylinder for a system with a secondary return circuit.
All electrical connections, including the immersion heater(s), must be wired by a qualified electrician in accordance with BS 7671; actual cable sizing should be calculated on site rather than assumed from generic figures.
Why Choose the JAB DUC 2 Direct
Duplex Stainless-Steel Shell
The duplex stainless-steel body resists pitting and stress corrosion far better than standard 304-grade tanks, giving reliable long-term performance in hard-water areas.
Electric-Only Heating
Purpose-built for properties where electricity is the only available heat source, with twin or triple factory-fitted immersion heaters as the sole means of heating the stored water.
Smart Immersion on Larger Sizes
The 170L–300L models are fitted with a smart immersion heater, giving more precise, programmable control over electric water heating than a standard thermostatic immersion.
Remote Expansion Vessel
The expansion vessel is supplied as a separate wall-mounted unit with its own bracket rather than clamped to the cylinder body, freeing up airing-cupboard space and easing servicing access.
Tariff-Flexible Multi-Element Heating
Twin 3kW immersions on the 90L–200L sizes step up to triple 3kW on the 250L and 300L models, allowing staged or multi-rate tariff heating strategies.
Full Unvented Kit Included
The complete unvented kit ships with every cylinder, so the installer isn't left sourcing safety-group components separately.
Sizes & Specification
| Capacity |
Height |
Diameter |
Immersion |
Reheat (10°C–60°C) |
Standing Heat Loss |
Full Weight |
| 90L |
750mm |
510mm |
2 x 3kW |
53 min |
1.59 kWh/24h |
119kg |
| 125L |
900mm |
510mm |
2 x 3kW |
73 min |
1.64 kWh/24h |
154kg |
| 150L |
1075mm |
510mm |
2 x 3kW |
87 min |
1.85 kWh/24h |
185kg |
| 170L |
1200mm |
510mm |
2 x 3kW* |
99 min |
1.97 kWh/24h |
208kg |
| 200L |
1500mm |
510mm |
2 x 3kW* |
116 min |
1.85 kWh/24h |
238kg |
| 250L |
1500mm |
580mm |
3 x 3kW* |
145 min |
2.00 kWh/24h |
299kg |
| 300L |
1750mm |
580mm |
3 x 3kW* |
175 min |
2.22 kWh/24h |
353kg |
*Smart immersion heater fitted on the 170L, 200L, 250L, and 300L models.
Connection Dimensions
| Capacity |
A |
B |
C |
D |
E |
| 90L |
171mm |
201mm |
421mm |
– |
551mm |
| 125L |
171mm |
201mm |
421mm |
– |
671mm |
| 150L |
171mm |
201mm |
621mm |
– |
876mm |
| 170L |
171mm |
201mm |
621mm |
– |
1026mm |
| 200L |
171mm |
201mm |
721mm |
1221mm |
1321mm |
| 250L |
193mm |
223mm |
643mm |
973mm |
1293mm |
| 300L |
193mm |
223mm |
643mm |
1253mm |
1543mm |
Technical Specification
| Construction |
| Cylinder Type |
Direct, unvented, duplex stainless-steel |
| Energy Efficiency Class |
C |
| Operating Pressure |
3 bar |
| Max Incoming Supply Pressure |
12 bar |
| Connections & Safety (All Sizes) |
| Hot Water Draw-Off |
22mm |
| Secondary Return |
22mm (standard on 200L+ only, see note above) |
| Cold Feed |
22mm |
| Temperature & Pressure Relief Valve |
1/2″, factory-set 7 bar / 90°C |
| Expansion Vessel |
Remote-mounted, wall bracket supplied |
| Unvented Kit |
Full kit supplied |
Frequently Asked Questions
Does this cylinder need a boiler connection?
No. This is a direct cylinder – it has no boiler coil and is heated solely by its factory-fitted immersion heaters, making it suited to properties where electricity is the only available heat source.
Does this cylinder come with a secondary return connection?
Not as standard on the 90L–170L sizes – the 22mm secondary return connection is only fitted as standard from 200L upwards. Check this before specifying if a secondary return circuit is required on a smaller cylinder.
How many immersion heaters does each size have?
The 90L–200L models have 2 x 3kW immersion heaters, while the 250L and 300L models step up to 3 x 3kW. The upper immersion on 170L–300L models is a smart, programmable unit.
Does this cylinder need to be installed by a qualified installer?
Yes. As an unvented hot water cylinder it must be installed, commissioned, and notified to Building Control by a G3-qualified (Benchmark) installer in line with Building Regulations Part G3.
How fast does this cylinder reheat?
Manufacturer-rated reheat time from 10°C to 60°C (based on two 3kW immersion elements) ranges from 53 minutes on the 90L model to 175 minutes on the 300L model; the 250L and 300L models' additional third element can improve on this when all elements run together.
What's the difference between the actual and nominal capacity?
The nominal litre rating is a rounded figure; the actual stored capacity is slightly lower once fittings are accounted for – for example, the “90L” model holds 89L, and the “300L” model holds 294L.
