Horizontal unvented cylinders

Our horizontal unvented cylinders are designed for installation in locations such as lofts and attics and are ideal for areas with restricted height such as basements. These horizontal unvented hot water cylinders for mains pressure hot water are manufactured in duplex stainless steel for long product life. They are ErP class “A” rated for energy-efficient operation and are indirect cylinders that can be supplied by various heat sources, including oil or gas boilers, heat pumps, or even solar water heating systems.

Horizontal cylinders 

Horizontal hot water cylinders are mainly useful when you have limited vertical space, such as in a loft or other height-restricted area, because they can fit where a standard upright cylinder may not. They also let you keep stored hot water in a compact footprint while still delivering strong hot water performance. They are useful for upgrades where the system needs to work around structural or height constraints.

Generally, most horizontal pressurised hot water cylinders are manufactured from stainless steel for durability and higher working pressures rather than copper.

However, vertical cylinders are generally more efficient than horizontal cylinders due to the natural stratification of hot water.

Loft installation considerations

If the horizontal unvented cylinder is going in a loft, extra checks are usually needed for access and flooring that is strong enough to carry it when full of water (please note that every litre of water weighs 1 kg, which needs to be added to the empty tank weight) and to meet servicing and maintenance requirements.

Unvented hot water benefits of horizontal cylinders

Unvented horizontal hot water cylinder systems are designed to provide full mains pressure and high flow rates to all taps, unlike vented systems, which use gravity, as unvented cylinders deliver hot water at the same pressure as the incoming mains supply.

They operate at high mains pressure, providing powerful, consistent hot water flow, i.e., mains pressure hot water with an indirect horizontal pressurised hot water cylinder.

Horizontal indirect unvented cylinder range

Our range of indirect unvented horizontal hot water cylinders consists of volumes from 180 to 500 litres, and all hot water storage units have a high energy efficiency (ErP “A”) rating for their heat loss / insulation values.

Quick sizing guide

Our 180L unvented indirect horizontal cylinder is suitable for a 2-bedroom, 1-bath/shower property.

Our 200L unvented indirect horizontal cylinder is suitable for a 3-bedroom + 2-bath/shower property.

Our 300L unvented indirect horizontal cylinder is suitable for a 4-bedroom, 2-bath/shower property.

Our 500L unvented indirect horizontal cylinder is designed for larger properties and can meet commercial hot water demands. 

Horizontal indirect unvented cylinder range	Volume (L) Actual	Diameter ØD (mm)	B = Length (mm)	DN (8&9)/(3&4)	Coil surface heating area (m²)	DN6 – Immersion heater port	Maximum Temp °C	Maximum Pressure (bar)	Empty weight (kg)
180L Horizontal indirect hot water cylinder – Duplex stainless steel	143	470	1836	1″	2	1 1/2″	95	6	38
200L Horizontal indirect hot water cylinder – Duplex stainless steel	193	560	1325	1″	2	1 1/2″	95	6	42
300L Horizontal indirect hot water cylinder – Duplex stainless steel	287	600	1560	1″	4	1 1/2″	95	6	70
500L Horizontal indirect hot water cylinder – Duplex stainless steel	500	700	1828	1″ / 1 1/4″	6.5	1 1/2″	95	6	88

Heat exchanger performance data for DHW heating

Based on a flow and return temperature to the heat exchanger coil of 80°C/60°C and raising the DHW from 10°C to 60°C, our unvented horizontal cylinders can produce some incredible heat outputs with mains pressure hot water and high flow rates.

180 Litre and 200 Litre horizontal cylinders = 33 kW 

300 Litre horizontal cylinder = 65 kW (this 300L horizontal unvented cylinder is our most popular seller). 

500 Litre horizontal cylinder = 106 kW (calculation shown below). 

If you have different flow and return temperatures or a desired final DHW temperature, we can input this data into the calculator to produce your exact results.

Due to the large heat exchanger coil surface area, these are perfectly suited as a horizontal hot water cylinder for a heat pump

Horizontal indirect unvented cylinders with bespoke options are available on request.

Stainless steel construction

Our units are manufactured in duplex stainless steel (2304: 23% chromium, 4% nickel, molybdenum-free stainless steel), making them designed and suitable for installation in soft or hard water areas.

The anti-corrosion qualities of Duplex 2304 are similar to those of stainless steel 316L. Nevertheless, compared to stainless steel 304, the mechanical characteristics, including the yield strength, are twice as high.

Horizontal hot water cylinder unvented system

Unvented cylinders must be installed in accordance with the relevant UK building regulations, especially “G3” in England and Wales (and in Scotland – Technical Standard Section 4 (Safety)). They need to be installed by a qualified installer who knows G3 regulations, because these cylinders require safety features like an expansion vessel and a pressure relief valve.

The unvented cylinders come complete with a full unvented kit, which includes a potable water expansion vessel, an inlet group valve, a tundish, and a temperature and pressure safety valve.

Horizontal vented hot water cylinder?

This horizontal cylinder range is what we supply for a horizontal vented hot water cylinder requirement; we just don’t supply the unvented kit that we would normally supply for the unvented option. It’s as simple as that.

Contact Flexiheat UK

For more detailed information, stock availability, delivery times, price or to purchase our cost-effective and energy-efficient indirect horizontal unvented cylinders, the ideal solution for height-restricted areas in flats, houses or even commercial water heating schemes.

Please contact our sales team at 01202 822221 or use our website’s email contact form to discuss your requirements.