The JAB DUC 2 Solar Twin Coil Indirect is an unvented hot water cylinder built to run from two independent heat sources – a solar thermal array and a gas or oil boiler – through separate internal coils, with a factory-fitted immersion heater as electric back-up. Available in 200L, 250L, and 300L capacities, it's built from duplex stainless-steel with a remote-mounted expansion vessel.
580mm
Diameter (All Sizes)
22mm
Secondary Return Fitted
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. Solar thermal circuit connections should be made by an installer competent in solar thermal systems.
Connection port angles vary by size: JAB's technical drawing for this range shows the flow and return spigots fitted at specific angles that differ between the 170L, 200L–300L, and 400L–500L diameter tiers. Always check the current manufacturer installation diagram for the exact angles on the specific size being fitted before finalising pipework runs.
All electrical connections, including the immersion heater, 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 Solar Twin Coil Indirect
Twin-Coil Design
Two independent internal coils let the cylinder be heated from two separate sources – typically a solar thermal array as the primary, low-carbon source and a gas or oil boiler as the secondary source – each with its own thermostat pocket for independent control.
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.
Solar-Optimised Coil Placement
The solar coil sits lower in the cylinder than the boiler coil, taking advantage of thermal stratification so the solar array can contribute useful heat even at lower output, before the boiler coil tops up the upper section.
Independent Immersion Back-Up
A factory-fitted immersion heater gives an independent electric back-up route to hot water if both the solar and boiler heat sources are unavailable.
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.
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 |
| 200L |
1120mm |
580mm |
| 250L |
1330mm |
580mm |
| 300L |
1650mm |
580mm |
Connection Dimensions
| Capacity |
A |
B |
C |
D |
E |
F |
G |
H |
I |
J |
| 200L |
190mm |
245mm |
390mm |
500mm |
545mm |
585mm |
780mm |
890mm |
890mm |
930mm |
| 250L |
190mm |
245mm |
390mm |
500mm |
500mm |
640mm |
890mm |
1025mm |
1025mm |
1140mm |
| 300L |
190mm |
245mm |
390mm |
500mm |
575mm |
640mm |
885mm |
1250mm |
1020mm |
1430mm |
Technical Specification
| Construction |
| Cylinder Type |
Indirect, unvented, duplex stainless-steel, twin-coil (solar + boiler) |
| Connections & Safety (All Sizes) |
| Hot Water Draw-Off |
22mm |
| Secondary Return |
22mm |
| Boiler Flow |
22mm |
| Boiler Return |
22mm |
| Solar Flow |
22mm |
| Solar Return |
22mm |
| Cold Feed |
22mm |
| Thermostat Pockets |
3 – one per coil, plus one for the immersion zone |
| Temperature & Pressure Relief Valve |
1/2″, factory-set 7 bar / 90°C |
| Immersion Heater |
Factory-fitted (back-up) |
| Expansion Vessel |
Remote-mounted, wall bracket supplied |
| Unvented Kit |
Full kit supplied |
Frequently Asked Questions
How does the twin-coil system work?
The lower coil connects to a solar thermal array, taking advantage of thermal stratification to draw useful heat even from moderate solar output, while the upper coil connects to a gas or oil boiler to top up the rest of the cylinder. Each coil has its own thermostat pocket for independent control.
What happens if there's no solar gain or boiler heat available?
The factory-fitted immersion heater provides independent electric back-up, so hot water is still available if both coils are temporarily out of use.
Do the connection ports have specific angles?
Yes. JAB's technical drawing for this range shows the flow and return spigots fitted at specific angles that vary by cylinder diameter tier. Always check the manufacturer's current installation diagram for the exact port angles on the size being installed before finalising pipework.
Does this cylinder come with a secondary return connection?
Yes, a 22mm secondary return connection is included on this range, positioned near the top of the cylinder alongside the hot draw-off.
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.
Can this cylinder be used without a solar array connected?
It can be run from the boiler coil and immersion alone, but the twin-coil design and pricing are aimed at installations that use both heat sources; if no solar array is planned, a single-coil JAB DUC 2 Indirect model may be a simpler fit.
