JAB DUC 2 Standard Direct Unvented Cylinders (60L-300L)

Description

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.

90–300L

Capacity Range

7

Sizes Available

2–3 x 3kW

Immersion (By Size)

53–175 min

Reheat Time (10°C–60°C)

7 bar / 90°C

T&P Relief Setting

Remote

Expansion Vessel

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.

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Insulation Level

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Average

Good (New Build)

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