The Joule Cyclone Plus Indirect Horizontal Unvented Cylinder is a mains-pressure hot water storage cylinder designed specifically for horizontal installation — lofts, underfloor voids, airing cupboards with limited headroom, and plant rooms where a vertical cylinder will not fit. Available in 120L, 150L, 180L, 210L, 250L and 300L, it delivers powerful, uninterrupted mains-pressure hot water to single or multiple outlets simultaneously. Built from duplex stainless steel with 316L stainless fittings and coil, it carries a fully transferable 25-year vessel guarantee. The Cyclone Plus adds a white "white-goods" outer casing and a coil-in-coil smooth tube heat exchanger for faster heat recovery compared to the standard Cyclone range. Pre-fitted removable support cradles, factory-fitted safety controls, a 3 kW Incoloy immersion heater, 100 % CFC/HCFC-free insulation and all connections on the front face are included as standard. KIWA independently tested to BS EN 12897:2006. WRAS approved. Building Regulation G3 compliant.
Horizontal
Space-saving format
25-year
Vessel guarantee
3.5 bar
Working pressure
10 bar
Max mains input
Duplex SS
316L fittings & coil
KIWA Tested
IEC 17065
⚠ G3-competent person installation required: Unvented hot water cylinders are a controlled service under Building Regulation G3 (England and Wales), Technical Standard P3 (Scotland) and Building Regulation P5 (Northern Ireland). Installation must be carried out by a G3-qualified installer.
ℹ 25-year vessel guarantee — register within 28 days: The stainless steel vessel carries a fully transferable 25-year guarantee against faulty materials or workmanship. Register online at register-products.joule.ie within 28 days of commissioning. Annual servicing by a competent person is required and the service log must be maintained. Expansion vessel, controls and immersion heater carry a 2-year guarantee.
⚠ Mains supply only — check water chemistry: Designed for mains supply only. Warranty requires mains water within: TDS ≤ 600 mg/L, total hardness ≤ 200 mg/L, chloride ≤ 300 mg/L, pH 6.5 – 9.5. In hard water areas a scale inhibitor on the cold feed is recommended.
Why Choose Horizontal? — Installation Scenarios
A horizontal cylinder solves space problems that a vertical unit cannot. All six sizes share the same 545 mm diameter — only the length changes. The critical constraint is therefore floor-to-ceiling clearance or access hatch width, not floor area.
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Loft conversions and roof spaces
Restricted headroom prevents a vertical cylinder. The horizontal format uses length rather than height, lying flat under the eaves. Cradles keep the cylinder stable on the loft floor. Insulate all exposed pipework to prevent frost damage.
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Underfloor voids and low plant areas
Properties with shallow underfloor service areas or low-ceiling plant rooms can accommodate a 545 mm-diameter horizontal cylinder where a 1,100 mm+ tall vertical unit would not pass.
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Airing cupboards with limited headroom
Older UK homes often have airing cupboards sized around smaller copper vented cylinders. A horizontal Cyclone Plus allows an unvented upgrade in the same footprint where a standard-height vertical unit is too tall.
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Tight access hatches and apertures
The pre-fitted cradles are removable. The bare cylinder body can be passed through a narrow loft hatch that would not accept the cylinder with cradles attached — cradles are then reattached in situ. All connections are on the front face: no rear or side access is needed once the cylinder is in position.
The installation surface must be capable of supporting the full weight when filled. Full weights range from approximately 150 kg (120L) to 362 kg (300L). A structural assessment of the installation surface is advisable for larger sizes.
Size Selection Guide
Cylinder size is determined by peak daily demand, number of occupants and bathrooms, and the recovery rate of the primary heat source. Figures below are for a boiler primary source (single daily heating cycle). For a heat pump primary, increase by one size to allow for slower coil recovery at lower primary temperatures.
Size
SKU
Length (A)
Empty weight
Full weight
Typical occupancy
120L
JCPIDHO120
900 mm
~30 kg
~150 kg
1 – 2 people
150L
JCPIDHO150
1,100 mm
39 kg
189 kg
1 – 2 people
180L
JCPIDHO180
1,280 mm
44.4 kg
224.4 kg
2 – 3 people
210L
JCPIDHO210
1,470 mm
48.4 kg
258.4 kg
3 – 4 people
250L
JCPIDHO250
1,720 mm
57.6 kg
307.6 kg
4 – 5 people
300L
JCPIDHO300
1,980 mm
61.6 kg
361.6 kg
5 – 6+ people
All sizes: diameter (B) 545 mm · Max mains input 10 bar · Operating pressure 7 bar · Working pressure 3.5 bar (with supplied inlet controls) · 1× 3 kW Incoloy immersion @ 230 V included in all sizes.
Key Features
Duplex Stainless Steel Body — 316L Fittings and Coil Throughout
The Cyclone Plus is constructed from duplex stainless steel — a two-phase alloy with substantially better corrosion resistance than standard 304-grade stainless used in many competitor cylinders. All internal fittings, coil connections and the primary coil itself use 316L grade stainless steel, which has superior chloride corrosion resistance compared to 304 or standard 316. This material specification underpins the 25-year vessel guarantee. Butt-welded and robotically welded throughout for consistent, defect-free joints at all seam locations.
Duplex SS body316L fittings and coil25-year vessel guarantee
The Cyclone Plus uses Joule’s coil-in-coil smooth tube primary coil. Joule identify smooth tube as the highest heat-transfer coil type available, offering better performance than corrugated tube coils commonly used in lower-cost cylinders. Smooth tube eliminates the dead-flow zones at corrugation valleys that reduce transfer efficiency in corrugated designs. The coil-in-coil configuration extends the flow path within a compact envelope, increasing primary-side velocity and dwell time for enhanced heat exchange. The primary coil is rated at up to 98 kW on the larger sizes, accommodating high-output boilers and heat pumps without restriction. A bespoke dip pipe improves the available hot water volume at each draw-off.
Coil-in-coil smooth tubeUp to 98 kW primary coilBespoke dip pipe
Horizontal Format with Removable Pre-Fitted Cradles
The cylinder ships with support cradles pre-fitted for immediate installation. The cradles are designed to be removed for access hatch transit: the bare cylinder body passes through a narrow loft hatch that cannot accommodate the full cradle width, then the cradles are reattached in position. Once installed, the cradles provide stable, level support on the floor or shelf. This is a practical necessity in the majority of UK loft installations where the access hatch is narrower than the cylinder with cradles attached.
Cradles pre-fittedCradles removable for transitStable horizontal support
All Connections on the Front Face — Single-Side Access Only
All plumbing connections — cold in, hot out, primary flow and return, immersion, expansion relief, T&P discharge — are grouped on the front face of the cylinder. This is essential for horizontal loft and void installations where rear and side access is impossible once the cylinder is in position. Single-side access means all pipework can be completed from one direction, and future annual servicing, valve testing and immersion replacement requires front access only. Colour-coded tapping collars identify each connection without ambiguity.
All connections on front faceSingle-side accessColour-coded collars
Mains Pressure Unvented — 3.5 Bar Working, Up to 10 Bar Mains Input
Connected directly to the mains, the Cyclone Plus delivers hot water at 3.5 bar working pressure (set by the factory inlet controls). This matches the cold water pressure throughout the property, so hot and cold are balanced — eliminating the lukewarm-water problem common with gravity-fed vented systems (typically 0.1 – 0.3 bar). Thermostatic bar mixer showers work correctly without a pump. The inlet controls can handle mains input up to 10 bar, providing resilience against pressure peaks. A minimum dynamic mains pressure of 1.5 bar and flow rate of 25 L/min is required.
3.5 bar working pressure10 bar max mainsBalanced hot/cold pressure
Factory-Fitted 3 kW Incoloy Immersion — Backup and Off-Peak Heating
A 3 kW Incoloy immersion heater with integral thermostat is factory-fitted to all six sizes. Incoloy (nickel-iron alloy) resists scale build-up at high temperatures more effectively than copper or plain stainless elements, making it well suited for hard water areas. The immersion serves as backup heating if the primary source fails and for off-peak tariff charging (overnight Economy 7, Octopus Go/Agile, or other cheap-rate periods). The immersion element is 400 mm long: the installer must provide 400 mm clear access at the immersion end for withdrawal during servicing.
Dense 50 mm polyurethane foam insulation, entirely free of CFCs and HCFCs, with ODP of zero and GWP of just 1. Low standing heat loss is increasingly significant when heat pumps are the primary source: lower primary temperatures mean slower charge cycles, so a cylinder that retains heat well between cycles reduces the frequency of heat pump starts and improves seasonal system efficiency. The white outer casing is durable, wipe-clean, giving the Cyclone Plus its distinctive white-goods appearance that blends into domestic utility spaces.
50 mm PU foam insulationODP 0, GWP 1White outer casing
Complete Factory-Preset Safety Controls Supplied
Every Cyclone Plus Horizontal ships with a complete unvented safety kit: inlet control group (pressure reducing valve, non-return valve, strainer), expansion vessel, expansion relief valve, temperature and pressure (T&P) relief valve, and 22 mm compression fittings. All devices are factory pre-set to correct operating parameters and must not be adjusted. Branded components from established manufacturers. One delivery contains everything needed for a G3-compliant installation — the installer does not need to source separate unvented kit components.
All Joule Cyclone cylinders are tested by KIWA to IEC 17065 accreditation standard, independently verifying compliance with all applicable UK product legislation and regulations. Tested to BS EN 12897:2006 (Specification for indirectly heated unvented closed storage water heaters). WRAS approved for connection to public water mains. Compliant with Building Regulation G3 (England/Wales), Technical Standard P3 (Scotland), Building Regulation P5 (Northern Ireland). Joule are a charter member of the Hot Water Association (HWA).
KIWA / IEC 17065BS EN 12897:2006WRASG3/P3/P5
Technical Specifications
Cylinder Construction
Body material
Duplex stainless steel
Fittings and coil
316L grade stainless steel
Welding
Butt-welded, robotically welded throughout
Outer casing
White polycarbonate — white goods finish
T&P safety cover
Grey polycarbonate plastic
Insulation
Type
100 % CFC/HCFC-free polyurethane foam
Thickness
50 mm
ODP / GWP
0 / 1
Heat Exchanger (Primary Coil)
Type
Coil-in-coil smooth tube — High Gain
Primary coil rating
Up to 98 kW (larger sizes)
Coil connections
22 mm compression fittings supplied
Immersion Heater
Element
1× 3 kW Incoloy @ 230 V
Thermostat
Integral thermostat included
Element length / access clearance required
400 mm
Pressures
Max mains input pressure
10 bar
Operating pressure
7 bar
Working pressure (with supplied inlet controls)
3.5 bar
Minimum dynamic mains pressure
1.5 bar
Minimum flow rate
25 L/min
Connections
Location
All on front face
Fittings
22 mm compression fittings supplied
Colour identification
Yes — colour-coded tapping collars
Dimensions — All Sizes, Diameter (B) 545 mm
120L length (A)
900 mm
150L length (A)
1,100 mm
180L length (A)
1,280 mm
210L length (A)
1,470 mm
250L length (A)
1,720 mm
300L length (A)
1,980 mm
Weights (empty / full)
120L
~30 kg / ~150 kg
150L
39 kg / 189 kg
180L
44.4 kg / 224.4 kg
210L
48.4 kg / 258.4 kg
250L
57.6 kg / 307.6 kg
300L
61.6 kg / 361.6 kg
Standards and Approvals
Building regulation
G3 (England/Wales) · P3 (Scotland) · P5 (N. Ireland)
Product standard
BS EN 12897:2006
Independent testing
KIWA · IEC 17065 accreditation
Water approval
WRAS approved
Warranty
Stainless steel vessel
25 years — fully transferable
Expansion vessel, controls, components
1 year
Registration
Online within 28 days of commissioning
Annual service
Required — service log must be maintained
Frequently Asked Questions
Why choose horizontal over vertical?
A horizontal cylinder is the right choice when headroom is the limiting constraint. All six sizes share a 545 mm diameter; only the length varies. In a typical loft, 545 mm clearance is achievable even where a 1,600 mm+ vertical cylinder would not fit under the rafters. The removable cradles allow the bare cylinder to pass through a narrow access hatch and be reassembled in situ — not possible with a vertical unit. If headroom is not a constraint, a vertical cylinder offers slightly better thermal stratification and draw-off efficiency.
Can this cylinder be used with a heat pump as the primary heat source?
Yes. The coil-in-coil smooth tube coil is designed to work with any air-to-water heat pump. At heat pump flow temperatures (45 – 55°C), recovery is slower than with a boiler (70 – 80°C primary). Size up by one step — for example, choose 250L instead of 210L for a 3 – 4 person household — when a heat pump is the sole primary heat source. The 3 kW immersion provides backup if the heat pump fails and can top up DHW overnight on a cheap tariff.
Does the complete safety kit come included?
Yes. Every Cyclone Plus Indirect Horizontal includes a complete unvented safety kit: inlet control group (pressure reducing valve, non-return valve, strainer), expansion vessel, expansion relief valve, T&P relief valve and 22 mm compression fittings. All devices are factory pre-set. The installer provides the discharge pipework run (D1 and D2) to a safe termination, plus any isolation valves and system pipework. No additional unvented kit components need to be sourced.
Who can legally install an unvented cylinder in the UK?
Only a G3-qualified competent person — a plumber or heating engineer holding a current G3 (Unvented Hot Water Systems Level 3) qualification or equivalent. Building Regulation G3 classifies unvented hot water as a controlled service. The installer must notify building control before installation (or self-certify via a registered Competent Person Scheme). DIY installation is not permitted and will void the manufacturer’s warranty. The Benchmark Commissioning Checklist must be completed and left with the homeowner.
What water quality does the cylinder need, and what about hard water areas?
The Joule warranty requires public mains water within: TDS ≤ 600 mg/L, total hardness ≤ 200 mg/L, chloride ≤ 300 mg/L, pH 6.5 – 9.5. Most UK mains supplies comply, but the South East, East Anglia and parts of the Midlands have notably hard water (often 200 – 350 mg/L). In hard water areas, Joule recommend a scale inhibitor on the cold feed. The 316L stainless body and coil offer better hard water resistance than copper, but scale on the immersion element is excluded from warranty cover regardless. For borehole or private water schemes, the Joule Wellmaster range must be used instead.
How do I register the 25-year warranty?
Register online at register-products.joule.ie within 28 days of commissioning. You will need the serial number from the cylinder badge, installation date, installer details and homeowner details. A completed warranty card copy should be emailed to warranty@joule.ie. The guarantee is fully transferable on property sale, provided annual servicing continues and the service log is maintained. The 25-year guarantee covers the stainless steel vessel only. Expansion vessel, controls and immersion carry a 1-year guarantee.
How does mains pressure hot water differ from my old gravity system?
A traditional gravity-fed vented system delivers hot water at the static head of the cold water tank above the outlet — typically 0.1 – 0.3 bar. Shower performance is poor, and hot and cold water pressures are badly mismatched. An unvented cylinder operates hot water at the same pressure as the cold mains — typically 2 – 3.5 bar. This gives dramatically improved flow at showers and taps, truly balanced hot and cold for thermostatic mixer showers (no cold water pump needed), and eliminates the cold water storage tank. The trade-offs are the G3 installation requirement and a mandatory annual service obligation.
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BTU & WATT Calculator
Room Dimensions
Room Type
Living Room
Bedroom
Kitchen
Bathroom
Conservatory
Hallway
Glazing Type
Single Glazed
Double Glazed
Triple Glazed
External Walls
0 Wall
1 Wall
2 Walls
3 Walls
4 Walls
Insulation Level
Poor
Average
Good (New Build)
Required Heating
0
Watts
0
BTUs
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