The JAB DUC 2 Indirect is a standard-format unvented hot water cylinder built for typical domestic installations, heated indirectly from a gas or oil-fired boiler and backed up by factory-fitted immersion heating. Available in seven capacities from 90L to 300L, it combines a duplex stainless-steel shell with a remote-mounted expansion vessel and a factory-set safety group.
1–2 x 3kW
Immersion (By Size)
26–40 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.
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 Indirect
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.
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.
Fast Reheat Across the Range
Reheat time from 10°C to 60°C stays within a tight 26–40 minute band across the whole capacity range, so larger sizes don't mean a proportionally longer wait for hot water.
Tariff-Flexible Immersion Heating
A single 3kW immersion gives back-up heating on the 90L–200L sizes, stepping up to 2 x 3kW on the 250L and 300L models to match the larger stored volume.
Factory-Set Safety Group
The temperature and pressure relief valve is factory-calibrated and tested before dispatch, removing a common on-site commissioning error and shortening installation time.
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 |
1 x 3kW |
26 min |
1.59 kWh/24h |
121kg |
| 125L |
900mm |
510mm |
1 x 3kW |
36 min |
1.64 kWh/24h |
156kg |
| 150L |
1075mm |
510mm |
1 x 3kW |
37 min |
1.85 kWh/24h |
187kg |
| 170L |
1200mm |
510mm |
1 x 3kW |
36 min |
1.97 kWh/24h |
210kg |
| 200L |
1500mm |
510mm |
1 x 3kW |
33 min |
1.85 kWh/24h |
240kg |
| 250L |
1500mm |
580mm |
2 x 3kW |
35 min |
2.00 kWh/24h |
301kg |
| 300L |
1750mm |
580mm |
2 x 3kW |
40 min |
2.22 kWh/24h |
355kg |
Connection Dimensions
| Capacity |
A |
B |
C |
D |
E |
F |
| 90L |
171mm |
201mm |
401mm |
497mm |
– |
551mm |
| 125L |
171mm |
201mm |
401mm |
497mm |
– |
671mm |
| 150L |
171mm |
201mm |
401mm |
497mm |
– |
876mm |
| 170L |
171mm |
201mm |
451mm |
601mm |
– |
1026mm |
| 200L |
171mm |
201mm |
451mm |
601mm |
1231mm |
1311mm |
| 250L |
193mm |
223mm |
553mm |
843mm |
973mm |
1293mm |
| 300L |
193mm |
223mm |
553mm |
843mm |
1253mm |
1543mm |
Technical Specification
| Construction |
| Cylinder Type |
Indirect, 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) |
| Boiler Flow |
22mm |
| Boiler Return |
22mm |
| 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 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.
What heat source does this cylinder use?
It's designed to be heated indirectly via a boiler coil connected to a gas or oil-fired boiler, with the immersion heater(s) providing independent electric back-up.
How many immersion heaters does each size have?
The 90L–200L models have a single 3kW immersion, while the 250L and 300L models have 2 x 3kW immersion heaters.
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?
Reheat time from 10°C to 60°C ranges from 26 minutes on the 90L model to 40 minutes on the 300L model, based on the manufacturer's rated coil performance.
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 the coil and fittings are accounted for – for example, the “90L” model holds 89L, and the “300L” model holds 294L.
