The Joule Cyclone Air Indirect unvented hot water cylinder range (100L–300L) delivers mains-pressure hot water for homes and light commercial properties, heated indirectly by a boiler, heat pump, or other compatible primary heat source. Built on a Duplex stainless steel vessel with a built-in expansion air bubble, the Cyclone Air removes the need for a separate external expansion vessel — keeping the installation footprint small and neat, in the same style as the market-leading Megaflo range. A pre-plumbed inlet control group, factory-fitted 3kW Incoloy immersion heater, and dense CFC/HCFC-free PU foam insulation round out a cylinder engineered for fast recovery, low standing losses, and a straightforward, repeatable install.
0.58–0.77m²
Coil Surface Area
20–50 min
Heat-Up Time 10→60°C
🔴 Professional installation required
This is an unvented hot water cylinder and is a controlled installation under Building Regulation G3 (England & Wales), Technical Standard P3 (Scotland), or Building Regulation P5 (Northern Ireland). It must be installed, commissioned, and serviced annually by a competent, G3-qualified installer, with local authority notification where required.
Duplex Stainless Steel Body
The vessel is manufactured from Duplex stainless steel, a grade chosen for its high resistance to pitting and chloride-driven corrosion — giving the cylinder a long working life even in harder water areas, without relying on a sacrificial anode.
Internal Expansion Air Bubble
A built-in expansion air bubble absorbs the volume increase as water heats, removing the need for a separate external expansion vessel. This keeps the airing cupboard or plant room footprint compact and avoids an extra component that could fail or need replacing.
Pre-Plumbed Inlet Control Group
The factory-fitted inlet control set (pressure reducing valve, check valve, expansion relief valve, and strainer) arrives pre-plumbed and tested, cutting install time and removing a common source of on-site plumbing errors.
High-Efficiency Indirect Coil
A smooth-tube indirect coil, sized between 0.58m² and 0.77m² depending on capacity, transfers heat from the boiler or heat pump primary circuit efficiently, giving 1st re-heat times of 14–35 minutes across the range.
3kW Incoloy Immersion Heater
A factory-fitted 3kW Incoloy immersion heater provides electric backup or off-peak water heating independent of the boiler, useful during servicing or as a renewable top-up source.
CFC/HCFC-Free PU Foam Insulation
Dense polyurethane foam insulation with zero ozone-depletion factor keeps standing heat losses down to 40–92W across the range, supporting the cylinder's B–C ErP rating band.
🟢 Coil sizing steps up with capacity
The 100L–170L models use a 0.58m² primary coil, while the 200L–300L models step up to 0.67–0.77m², giving the larger cylinders proportionally faster recovery when paired with a suitably sized boiler or heat pump.
| Construction |
| Vessel material |
Duplex stainless steel |
| Insulation |
CFC/HCFC-free PU foam, zero ozone-depletion factor |
| Cylinder diameter |
540mm (all capacities) |
| Casing finish |
White “domestic appliance” style outer casing |
| Heating & Coil |
| Heat source |
Boiler, heat pump, or other compatible thermostatically-controlled primary source |
| Primary coil surface area (100–170L) |
0.58m² |
| Primary coil surface area (200–300L) |
0.67–0.77m² |
| Primary coil operating pressure (max) |
6 bar (0.6MPa) |
| Immersion heater |
3kW, single-phase, 230V a.c., 50/60Hz, factory-fitted (Incoloy) |
| Thermostat set temperature |
60°C (dual cylinder stat, indirect models) |
| Pressure & Safety |
| Inlet water pressure |
Max 7 bar (0.7MPa) / Min 3 bar (0.3MPa) |
| Inlet control set operating pressure |
3 bar |
| Expansion relief valve setting |
8 bar (0.8MPa) |
| Maximum design pressure |
6 bar (0.6MPa) |
| T&P relief valve setting |
10 bar / 90°C (1.0MPa) |
| Standing loss (100L–300L) |
40W – 92W |
| Standards & Warranty |
| Tested to |
BS EN 12897:2016 |
| Building Regulations |
G3 (England & Wales), P3 (Scotland), P5 (Northern Ireland) |
| Cylinder guarantee |
25 years, fully transferable |
| Controls & components guarantee |
2 years |
| Charter membership |
Hot Water Association (HWA) charter member manufacturer |
🟡 Confirm the exact model code before ordering
Joule's published nominal capacities (100L, 125L, 150L, 170L, 200L, 250L, 300L) are rounded figures.
| Capacity |
Height (mm) |
Empty / Full Weight (kg) |
ErP Rating |
Standing Loss (W) |
Heat-Up Time 10→60°C |
| 100L |
950 |
47 / 162 |
B |
40 |
25 min |
| 125L |
1030 |
48 / 157 |
B |
48 |
20 min |
| 150L |
1190 |
50 / 186 |
B |
51 |
26 min |
| 170L |
1310 |
54 / 231 |
B |
54 |
33 min |
| 200L |
1490 |
58 / 253 |
C |
77 |
37 min |
| 250L |
1815 |
64 / 296 |
C |
85 |
43 min |
| 300L |
2060 |
74 / 348 |
C |
92 |
50 min |
What sizes does the Cyclone Air Indirect range come in?
The range covers seven nominal capacities: 100L, 125L, 150L, 170L, 200L, 250L, and 300L. All share a 540mm diameter, with height increasing from 950mm (100L) to 2060mm (300L).
Does this cylinder need a separate external expansion vessel?
No. The Cyclone Air's internal expansion air bubble absorbs the increase in water volume as it heats, so a separate external expansion vessel is not required — unlike many standard unvented cylinders.
What's the difference between Direct and Indirect Cyclone Air cylinders?
The Indirect version (this product) is heated via a coil connected to a boiler, heat pump, or similar primary heat source, with the immersion heater providing backup. The Direct version has no coil and relies solely on electric immersion heating.
Can this cylinder be used with a heat pump?
Yes. The indirect coil is compatible with heat pump primary circuits provided the heat source is under effective thermostatic control and the system is designed to suit the cylinder's coil surface area and expected recovery time.
Who can install this cylinder?
As an unvented cylinder, installation is a controlled service under Building Regulation G3 and equivalent regional standards. It must be installed and commissioned by a competent, G3-qualified installer, and serviced annually to keep the manufacturer warranty valid.
What's covered under the 25-year warranty?
The stainless steel vessel carries a fully transferable 25-year guarantee against faulty materials or manufacture, provided the cylinder is installed per the manufacturer's instructions and serviced annually. The unvented kit and other fitted components carry a separate 2-year guarantee.
