Ultraflow Horizontal Indirect Unvented Hot Water Cylinder 120L–500L
The Ultraflow Horizontal Indirect Unvented Hot Water Cylinder is a UK-manufactured, duplex stainless steel hot water storage solution built specifically for installations where headroom is limited or a conventional upright cylinder simply will not fit. Available in capacities from 120 to 500 litres, the range covers everything from a compact two-bedroom flat to a large family home. Every cylinder is supplied complete with a full G3-compliant unvented kit, mounting cradles, and a highly efficient indirect coil — and is backed by an industry-leading 25-year cylinder warranty.
Horizontal cylinders solve a very specific problem: limited vertical headroom. Loft conversions, plant rooms with low ceiling joists, cupboards beneath stairs, and boiler-adjacent utility spaces often cannot accommodate a tall upright cylinder. The Ultraflow horizontal range is mounted on its side using supplied cradles — positioned wherever the available horizontal run allows — without sacrificing any of the performance expected from a high-quality unvented system.
Manufactured from duplex stainless steel and insulated with 50mm closed-cell foam, these cylinders deliver the same excellent heat retention, corrosion resistance, and reheat performance as Ultraflow's upright counterparts. The highly efficient indirect coil ensures rapid heat transfer from any boiler or primary heat source, while the complete G3 kit means the installer arrives with everything needed to commission a compliant unvented installation.
Duplex stainless steel offers superior corrosion resistance compared with standard 316L grades — a significant advantage in hard-water areas and wherever aggressive water chemistry could compromise a conventional cylinder over time. The material is specified for longevity, not just compliance, which is why Ultraflow can back it with a 25-year cylinder guarantee.
All horizontal cylinders are supplied with mounting cradles as standard. The cradles add 105mm to the installed height (i.e. the cylinder diameter plus cradle depth) and allow the cylinder to be secured safely on its side without the need for bespoke fabrication on site.
Every cylinder ships with a full high-quality unvented kit — including the pressure reducing valve, expansion vessel, inlet control set, tundish, T&P relief valve, and associated fittings — so the installer has everything needed to commission a G3-compliant installation straight from the box.
The large-surface-area primary coil ensures fast heat transfer from the boiler into stored water, minimising reheat time and reducing fuel consumption. Coil ratings range from 15.8kW (120L) up to 28.49kW (500L), delivering rapid recovery even during periods of high demand.
50mm of premium closed-cell foam insulation wraps the full body of every cylinder, minimising standing heat losses and keeping stored water at temperature for longer — translating directly into lower energy bills across the life of the product.
A high-quality 3kW Incoloy immersion heater is fitted as standard, providing a direct electric backup heat source independent of the boiler. Cylinders 150L and above are supplied with two immersion heaters for top-and-bottom flexibility and legionella control compliance.
A mechanical cylinder thermostat is included as standard, giving accurate temperature monitoring and control of the immersion heating circuit. This supports compliance with HSE legionella guidance on maintaining stored water at 60°C.
A secondary return connection is fitted as standard on 200L and above, enabling a secondary circulation loop for instant-hot-water performance across larger properties without the need for a modified cylinder or additional fitting.
All cylinders carry WRAS approval and are manufactured to BS EN 12897:2006 and 12897:2016, with full ErP energy labelling. Building Regulations compliance (Part L and G3) is verified by NSF Labs, making specification and sign-off straightforward for both installer and Building Control.
Ultraflow cylinders are manufactured in the UK and held in significant stock at distribution centres in Enfield and Northampton. Same-day or next-day despatch is available on most lines, minimising downtime on site and supporting fast-turnaround jobs.
Cylinders can be specified with optional upgrades on request: Highflow 1" hot and cold connections with 28mm inlet group, 6kW Incoloy immersion, 3kW or 6kW Titanium immersion elements, additional immersion heaters, and a larger capacity expansion vessel for high-volume systems.
Unvented hot water cylinders must be installed by a qualified unvented cylinder engineer holding a current G3 competency certificate (e.g. CIPHE, BPEC, City & Guilds 6089 or equivalent). Installation must comply with Part G of the Building Regulations and the Water Supply (Water Fittings) Regulations 1999. All dimensions in the specification table are to be used as guidelines only.
All horizontal cylinders are supplied with mounting cradles. Add 105mm to the cylinder diameter to calculate the installed footprint height — a 545mm diameter cylinder on its cradles occupies approximately 650mm of vertical clearance; the 690mm diameter models (400L and 500L) require approximately 795mm. Confirm headroom before ordering.
| Capacity | Code | Diameter (mm) | Length (mm) | Coil Rating (kW) | Reheat (mins) | Immersions | Heat Loss (kWh/24h) | ErP | Weight (kg) |
|---|---|---|---|---|---|---|---|---|---|
| 120L | UIH120 | 545 | 915 | 15.80 | 17 | 1 | 1.30 | C | 27 |
| 150L | UIH150 | 545 | 1100 | 16.50 | 22 | 2 | 1.56 | C | 33 |
| 180L | UIH180 | 545 | 1284 | 18.00 | 22 | 2 | 1.66 | C | 39 |
| 200L | UIH200 | 545 | 1414 | 19.94 | 25 | 2 | 1.87 | C | 40 |
| 250L | UIH250 | 545 | 1722 | 20.68 | 28 | 2 | 2.11 | C | 46 |
| 300L | UIH300 | 545 | 1975 | 23.57 | 32 | 2 | 2.30 | C | 50 |
| 400L (1" connections) | UIH400 | 690 | 1580 | 27.58 | 52 | 2 | 2.42 | C | 76 |
| 500L (1" connections) | UIH500 | 690 | 1910 | 28.49 | 54 | 2 | 2.56 | C | 92 |
What is the main advantage of a horizontal cylinder over an upright?
A horizontal cylinder is specified when vertical headroom is insufficient for an upright model. Loft conversions, cupboards beneath sloping rooflines, and plant rooms with low ceilings are the most common applications. The cylinder lays on its side in mounting cradles, requiring only enough headroom to accommodate its diameter plus the 105mm cradle depth. Performance is equivalent to an upright indirect cylinder of the same capacity.
Do the mounting cradles add to the installed height?
Yes. The supplied cradles add 105mm to the installed height — which for a horizontal cylinder is its diameter. A 545mm diameter cylinder therefore requires approximately 650mm of vertical clearance; the 690mm diameter models (400L and 500L) require approximately 795mm. Always measure carefully before ordering.
What size cylinder do I need?
A common rule of thumb is to allow 45–50 litres of stored hot water per person. A two-person property typically suits 120L; a family of four, 200–250L; larger households or properties with multiple bathrooms should consider 300L or above. For commercial or HMO applications, our team can assist with a detailed sizing calculation.
Why is duplex stainless steel better than standard stainless?
Duplex stainless steel has a mixed austenitic-ferritic microstructure that gives it approximately twice the tensile strength and significantly better resistance to chloride corrosion compared with standard 316L austenitic stainless. This makes it particularly well suited to UK hard-water areas and coastal environments, and is a key reason Ultraflow can offer a 25-year cylinder warranty.
Is everything I need for a G3 installation included?
Yes — the complete unvented kit is supplied with every cylinder. This includes the inlet control set, pressure reducing valve, expansion vessel, tundish, temperature and pressure relief valve, and associated fittings required to comply with Part G of the Building Regulations. The installer does not need to source these components separately.
Can I upgrade the immersion heater?
Yes. Upgrades are available on request, including 6kW Incoloy, 3kW Titanium, and 6kW Titanium elements. Titanium immersion heaters offer extended service life in particularly aggressive water conditions. Additional immersion heater ports can also be specified for certain configurations.
Are the dimensions guaranteed?
Ultraflow state that all dimensions are to be used as guidelines only. Minor variation can occur between production batches. Always confirm final dimensions with Ultraflow before committing to a particularly tight installation, especially where clearances are critical.
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Ultraflow Horizontal Indirect Unvented Hot Water Cylinder 120L–500L
The Ultraflow Horizontal Indirect Unvented Hot Water Cylinder is a UK-manufactured, duplex stainless steel hot water storage solution built specifically for installations where headroom is limited or a conventional upright cylinder simply will not fit. Available in capacities from 120 to 500 litres, the range covers everything from a compact two-bedroom flat to a large family home. Every cylinder is supplied complete with a full G3-compliant unvented kit, mounting cradles, and a highly efficient indirect coil — and is backed by an industry-leading 25-year cylinder warranty.
Horizontal cylinders solve a very specific problem: limited vertical headroom. Loft conversions, plant rooms with low ceiling joists, cupboards beneath stairs, and boiler-adjacent utility spaces often cannot accommodate a tall upright cylinder. The Ultraflow horizontal range is mounted on its side using supplied cradles — positioned wherever the available horizontal run allows — without sacrificing any of the performance expected from a high-quality unvented system.
Manufactured from duplex stainless steel and insulated with 50mm closed-cell foam, these cylinders deliver the same excellent heat retention, corrosion resistance, and reheat performance as Ultraflow's upright counterparts. The highly efficient indirect coil ensures rapid heat transfer from any boiler or primary heat source, while the complete G3 kit means the installer arrives with everything needed to commission a compliant unvented installation.
Duplex stainless steel offers superior corrosion resistance compared with standard 316L grades — a significant advantage in hard-water areas and wherever aggressive water chemistry could compromise a conventional cylinder over time. The material is specified for longevity, not just compliance, which is why Ultraflow can back it with a 25-year cylinder guarantee.
All horizontal cylinders are supplied with mounting cradles as standard. The cradles add 105mm to the installed height (i.e. the cylinder diameter plus cradle depth) and allow the cylinder to be secured safely on its side without the need for bespoke fabrication on site.
Every cylinder ships with a full high-quality unvented kit — including the pressure reducing valve, expansion vessel, inlet control set, tundish, T&P relief valve, and associated fittings — so the installer has everything needed to commission a G3-compliant installation straight from the box.
The large-surface-area primary coil ensures fast heat transfer from the boiler into stored water, minimising reheat time and reducing fuel consumption. Coil ratings range from 15.8kW (120L) up to 28.49kW (500L), delivering rapid recovery even during periods of high demand.
50mm of premium closed-cell foam insulation wraps the full body of every cylinder, minimising standing heat losses and keeping stored water at temperature for longer — translating directly into lower energy bills across the life of the product.
A high-quality 3kW Incoloy immersion heater is fitted as standard, providing a direct electric backup heat source independent of the boiler. Cylinders 150L and above are supplied with two immersion heaters for top-and-bottom flexibility and legionella control compliance.
A mechanical cylinder thermostat is included as standard, giving accurate temperature monitoring and control of the immersion heating circuit. This supports compliance with HSE legionella guidance on maintaining stored water at 60°C.
A secondary return connection is fitted as standard on 200L and above, enabling a secondary circulation loop for instant-hot-water performance across larger properties without the need for a modified cylinder or additional fitting.
All cylinders carry WRAS approval and are manufactured to BS EN 12897:2006 and 12897:2016, with full ErP energy labelling. Building Regulations compliance (Part L and G3) is verified by NSF Labs, making specification and sign-off straightforward for both installer and Building Control.
Ultraflow cylinders are manufactured in the UK and held in significant stock at distribution centres in Enfield and Northampton. Same-day or next-day despatch is available on most lines, minimising downtime on site and supporting fast-turnaround jobs.
Cylinders can be specified with optional upgrades on request: Highflow 1" hot and cold connections with 28mm inlet group, 6kW Incoloy immersion, 3kW or 6kW Titanium immersion elements, additional immersion heaters, and a larger capacity expansion vessel for high-volume systems.
Unvented hot water cylinders must be installed by a qualified unvented cylinder engineer holding a current G3 competency certificate (e.g. CIPHE, BPEC, City & Guilds 6089 or equivalent). Installation must comply with Part G of the Building Regulations and the Water Supply (Water Fittings) Regulations 1999. All dimensions in the specification table are to be used as guidelines only.
All horizontal cylinders are supplied with mounting cradles. Add 105mm to the cylinder diameter to calculate the installed footprint height — a 545mm diameter cylinder on its cradles occupies approximately 650mm of vertical clearance; the 690mm diameter models (400L and 500L) require approximately 795mm. Confirm headroom before ordering.
| Capacity | Code | Diameter (mm) | Length (mm) | Coil Rating (kW) | Reheat (mins) | Immersions | Heat Loss (kWh/24h) | ErP | Weight (kg) |
|---|---|---|---|---|---|---|---|---|---|
| 120L | UIH120 | 545 | 915 | 15.80 | 17 | 1 | 1.30 | C | 27 |
| 150L | UIH150 | 545 | 1100 | 16.50 | 22 | 2 | 1.56 | C | 33 |
| 180L | UIH180 | 545 | 1284 | 18.00 | 22 | 2 | 1.66 | C | 39 |
| 200L | UIH200 | 545 | 1414 | 19.94 | 25 | 2 | 1.87 | C | 40 |
| 250L | UIH250 | 545 | 1722 | 20.68 | 28 | 2 | 2.11 | C | 46 |
| 300L | UIH300 | 545 | 1975 | 23.57 | 32 | 2 | 2.30 | C | 50 |
| 400L (1" connections) | UIH400 | 690 | 1580 | 27.58 | 52 | 2 | 2.42 | C | 76 |
| 500L (1" connections) | UIH500 | 690 | 1910 | 28.49 | 54 | 2 | 2.56 | C | 92 |
What is the main advantage of a horizontal cylinder over an upright?
A horizontal cylinder is specified when vertical headroom is insufficient for an upright model. Loft conversions, cupboards beneath sloping rooflines, and plant rooms with low ceilings are the most common applications. The cylinder lays on its side in mounting cradles, requiring only enough headroom to accommodate its diameter plus the 105mm cradle depth. Performance is equivalent to an upright indirect cylinder of the same capacity.
Do the mounting cradles add to the installed height?
Yes. The supplied cradles add 105mm to the installed height — which for a horizontal cylinder is its diameter. A 545mm diameter cylinder therefore requires approximately 650mm of vertical clearance; the 690mm diameter models (400L and 500L) require approximately 795mm. Always measure carefully before ordering.
What size cylinder do I need?
A common rule of thumb is to allow 45–50 litres of stored hot water per person. A two-person property typically suits 120L; a family of four, 200–250L; larger households or properties with multiple bathrooms should consider 300L or above. For commercial or HMO applications, our team can assist with a detailed sizing calculation.
Why is duplex stainless steel better than standard stainless?
Duplex stainless steel has a mixed austenitic-ferritic microstructure that gives it approximately twice the tensile strength and significantly better resistance to chloride corrosion compared with standard 316L austenitic stainless. This makes it particularly well suited to UK hard-water areas and coastal environments, and is a key reason Ultraflow can offer a 25-year cylinder warranty.
Is everything I need for a G3 installation included?
Yes — the complete unvented kit is supplied with every cylinder. This includes the inlet control set, pressure reducing valve, expansion vessel, tundish, temperature and pressure relief valve, and associated fittings required to comply with Part G of the Building Regulations. The installer does not need to source these components separately.
Can I upgrade the immersion heater?
Yes. Upgrades are available on request, including 6kW Incoloy, 3kW Titanium, and 6kW Titanium elements. Titanium immersion heaters offer extended service life in particularly aggressive water conditions. Additional immersion heater ports can also be specified for certain configurations.
Are the dimensions guaranteed?
Ultraflow state that all dimensions are to be used as guidelines only. Minor variation can occur between production batches. Always confirm final dimensions with Ultraflow before committing to a particularly tight installation, especially where clearances are critical.
Product Information
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Shipping & Returns
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Description
The Ultraflow Horizontal Indirect Unvented Hot Water Cylinder is a UK-manufactured, duplex stainless steel hot water storage solution built specifically for installations where headroom is limited or a conventional upright cylinder simply will not fit. Available in capacities from 120 to 500 litres, the range covers everything from a compact two-bedroom flat to a large family home. Every cylinder is supplied complete with a full G3-compliant unvented kit, mounting cradles, and a highly efficient indirect coil — and is backed by an industry-leading 25-year cylinder warranty.
Horizontal cylinders solve a very specific problem: limited vertical headroom. Loft conversions, plant rooms with low ceiling joists, cupboards beneath stairs, and boiler-adjacent utility spaces often cannot accommodate a tall upright cylinder. The Ultraflow horizontal range is mounted on its side using supplied cradles — positioned wherever the available horizontal run allows — without sacrificing any of the performance expected from a high-quality unvented system.
Manufactured from duplex stainless steel and insulated with 50mm closed-cell foam, these cylinders deliver the same excellent heat retention, corrosion resistance, and reheat performance as Ultraflow's upright counterparts. The highly efficient indirect coil ensures rapid heat transfer from any boiler or primary heat source, while the complete G3 kit means the installer arrives with everything needed to commission a compliant unvented installation.
Duplex stainless steel offers superior corrosion resistance compared with standard 316L grades — a significant advantage in hard-water areas and wherever aggressive water chemistry could compromise a conventional cylinder over time. The material is specified for longevity, not just compliance, which is why Ultraflow can back it with a 25-year cylinder guarantee.
All horizontal cylinders are supplied with mounting cradles as standard. The cradles add 105mm to the installed height (i.e. the cylinder diameter plus cradle depth) and allow the cylinder to be secured safely on its side without the need for bespoke fabrication on site.
Every cylinder ships with a full high-quality unvented kit — including the pressure reducing valve, expansion vessel, inlet control set, tundish, T&P relief valve, and associated fittings — so the installer has everything needed to commission a G3-compliant installation straight from the box.
The large-surface-area primary coil ensures fast heat transfer from the boiler into stored water, minimising reheat time and reducing fuel consumption. Coil ratings range from 15.8kW (120L) up to 28.49kW (500L), delivering rapid recovery even during periods of high demand.
50mm of premium closed-cell foam insulation wraps the full body of every cylinder, minimising standing heat losses and keeping stored water at temperature for longer — translating directly into lower energy bills across the life of the product.
A high-quality 3kW Incoloy immersion heater is fitted as standard, providing a direct electric backup heat source independent of the boiler. Cylinders 150L and above are supplied with two immersion heaters for top-and-bottom flexibility and legionella control compliance.
A mechanical cylinder thermostat is included as standard, giving accurate temperature monitoring and control of the immersion heating circuit. This supports compliance with HSE legionella guidance on maintaining stored water at 60°C.
A secondary return connection is fitted as standard on 200L and above, enabling a secondary circulation loop for instant-hot-water performance across larger properties without the need for a modified cylinder or additional fitting.
All cylinders carry WRAS approval and are manufactured to BS EN 12897:2006 and 12897:2016, with full ErP energy labelling. Building Regulations compliance (Part L and G3) is verified by NSF Labs, making specification and sign-off straightforward for both installer and Building Control.
Ultraflow cylinders are manufactured in the UK and held in significant stock at distribution centres in Enfield and Northampton. Same-day or next-day despatch is available on most lines, minimising downtime on site and supporting fast-turnaround jobs.
Cylinders can be specified with optional upgrades on request: Highflow 1" hot and cold connections with 28mm inlet group, 6kW Incoloy immersion, 3kW or 6kW Titanium immersion elements, additional immersion heaters, and a larger capacity expansion vessel for high-volume systems.
Unvented hot water cylinders must be installed by a qualified unvented cylinder engineer holding a current G3 competency certificate (e.g. CIPHE, BPEC, City & Guilds 6089 or equivalent). Installation must comply with Part G of the Building Regulations and the Water Supply (Water Fittings) Regulations 1999. All dimensions in the specification table are to be used as guidelines only.
All horizontal cylinders are supplied with mounting cradles. Add 105mm to the cylinder diameter to calculate the installed footprint height — a 545mm diameter cylinder on its cradles occupies approximately 650mm of vertical clearance; the 690mm diameter models (400L and 500L) require approximately 795mm. Confirm headroom before ordering.
| Capacity | Code | Diameter (mm) | Length (mm) | Coil Rating (kW) | Reheat (mins) | Immersions | Heat Loss (kWh/24h) | ErP | Weight (kg) |
|---|---|---|---|---|---|---|---|---|---|
| 120L | UIH120 | 545 | 915 | 15.80 | 17 | 1 | 1.30 | C | 27 |
| 150L | UIH150 | 545 | 1100 | 16.50 | 22 | 2 | 1.56 | C | 33 |
| 180L | UIH180 | 545 | 1284 | 18.00 | 22 | 2 | 1.66 | C | 39 |
| 200L | UIH200 | 545 | 1414 | 19.94 | 25 | 2 | 1.87 | C | 40 |
| 250L | UIH250 | 545 | 1722 | 20.68 | 28 | 2 | 2.11 | C | 46 |
| 300L | UIH300 | 545 | 1975 | 23.57 | 32 | 2 | 2.30 | C | 50 |
| 400L (1" connections) | UIH400 | 690 | 1580 | 27.58 | 52 | 2 | 2.42 | C | 76 |
| 500L (1" connections) | UIH500 | 690 | 1910 | 28.49 | 54 | 2 | 2.56 | C | 92 |
What is the main advantage of a horizontal cylinder over an upright?
A horizontal cylinder is specified when vertical headroom is insufficient for an upright model. Loft conversions, cupboards beneath sloping rooflines, and plant rooms with low ceilings are the most common applications. The cylinder lays on its side in mounting cradles, requiring only enough headroom to accommodate its diameter plus the 105mm cradle depth. Performance is equivalent to an upright indirect cylinder of the same capacity.
Do the mounting cradles add to the installed height?
Yes. The supplied cradles add 105mm to the installed height — which for a horizontal cylinder is its diameter. A 545mm diameter cylinder therefore requires approximately 650mm of vertical clearance; the 690mm diameter models (400L and 500L) require approximately 795mm. Always measure carefully before ordering.
What size cylinder do I need?
A common rule of thumb is to allow 45–50 litres of stored hot water per person. A two-person property typically suits 120L; a family of four, 200–250L; larger households or properties with multiple bathrooms should consider 300L or above. For commercial or HMO applications, our team can assist with a detailed sizing calculation.
Why is duplex stainless steel better than standard stainless?
Duplex stainless steel has a mixed austenitic-ferritic microstructure that gives it approximately twice the tensile strength and significantly better resistance to chloride corrosion compared with standard 316L austenitic stainless. This makes it particularly well suited to UK hard-water areas and coastal environments, and is a key reason Ultraflow can offer a 25-year cylinder warranty.
Is everything I need for a G3 installation included?
Yes — the complete unvented kit is supplied with every cylinder. This includes the inlet control set, pressure reducing valve, expansion vessel, tundish, temperature and pressure relief valve, and associated fittings required to comply with Part G of the Building Regulations. The installer does not need to source these components separately.
Can I upgrade the immersion heater?
Yes. Upgrades are available on request, including 6kW Incoloy, 3kW Titanium, and 6kW Titanium elements. Titanium immersion heaters offer extended service life in particularly aggressive water conditions. Additional immersion heater ports can also be specified for certain configurations.
Are the dimensions guaranteed?
Ultraflow state that all dimensions are to be used as guidelines only. Minor variation can occur between production batches. Always confirm final dimensions with Ultraflow before committing to a particularly tight installation, especially where clearances are critical.
