Twin Coil Cylinders Vented or Unvented

Twin coil cylinder range from 300 to 6,000 litres from Flexiheat UK

A twin coil cylinder or a twin coil hot water tank is a hot water cylinder that has a twin coil or two inter wound coils installed within the hot water cylinder, which indirectly heats the domestic water inside the tank. They can be unvented or a vented cylinder.

They are intended for utilizing two external energy sources combined (a traditional boiler, solar thermal, heat pump, etc.) that heat the water that is stored inside the tank by passing hot water or fluids through the internal coils to heat the domestic water inside.

More commonly, the water is heated indirectly by a traditional boiler be it a gas boiler, wood burner, or an oil fired boiler suitable to feed the appropriate power to the upper coil, sometimes referred to as the boiler coil, whilst the lower coil of the twin coil hot water cylinder is often powered by solar panels or heat pump heating systems (air source heat pumps or ground source heat pumps), which are low-carbon, and is often referred to as the solar coil.

Although you can also use this range as solar cylinders, with both coils being fed by a solar system.

These units are designed to have the domestic hot water heated indirectly and are suitable for both gravity and pumped heating systems.

Dual coil hot water heating systems

Whichever way you want to power our twin coil cylinder range will depend on the heating systems available, such as heated water via a traditional boiler central heating or solar heating system, and you can also have a backup hot water heating via an immersion heater or immersion heaters depending on the dual coil hot water cylinders size.

Twin coil hot water cylinder

Optionally, an immersion heater or ceramic electrical heating elements can be installed into the cylinder via the immersion bosses to top up a heat pump or solar system, or to back up a boiler in the event of a boiler breakdown to ensure heated water.

Our boiler coil or solar coil (solar thermal), both have a 1″ bsp coil suitable for a pressure of 25 Bar and a temperature of 200C.

This hot water cylinders range has an ErP rating of “B” or “C” for low heat loss depending on the size of the model and includes one immersion bosses for an optional electric immersion heaters to back up or supplement any solar thermal systems.

Users continue to have many benefits by saving money with reduce energy bills throughout the storage tank’s lifespan thanks to the over dimensioned, rigid, mould-injected PU thermal insulation, which keeps DHW storage temperature constant for extended periods of time without requiring any additional energy input by reducing any heat loss.

Hot water cylinder twin coil range

From 300 litres to 1,500 litres, with high efficiency heat exchangers with a large surface area. Designated the CV- M” range – these cylinders are suitable for a pumped heating systems or a gravity heating system to feed the coils.

Our dual coil cylinders feature two separate coils, rather than two inter wound coils that can affect each other’s performance.

The thermal insulation is rigid, mould-injected PU (CFC/HCFC-free, 0.025 W/mºK) for low heat loss, and covered in an aesthetically pleasing white case finish.

Optional immersion heater – for back up heating, especially if you’re using these cylinders as solar cylinders only i.e. using solar to feed the traditional boiler coil at the top of the unit.

These dual coil cylinders all come with extra bosses such as a secondary return connection – 1″ bsp hot water return for models 300 to 500 litres, and 1 1/2″ bsp hot water return for models 800 to 1,500 litres.

Depending on the size our hot water cylinder may be fitted with extra immersion bosses, or extra bosses for temperature sensors as bespoke options and come with white case finish.

Optional 400mm inspection and clean out port on our 800,1000 and 1500 Litre volume cylinders M2B version – the standard cleanout port is 146mm (J) on the rest of the range.

Technical dimension data

All hot water cylinders have 25mm or 1″ BSP hot water connections to the each heat exchanger -“tm” connections can be used for a thermostat. “EH” is the immersion heater connection.

The 800 and 1000 litre capacity tanks include a removable insulation system that allows them to pass through 800 mm wide doors.

Dual coil cylinders performance based on 85C primary flow 

With each 1″ bsp coil suitable for temperatures up to 200C – most commonly they are fed at lower temperatures – i.e., 85C or so

Domestic water heating performance based on a primary flow of 85C to both 1″ bsp coils which indirectly heats the domestic water inside the tank.

Cylinder coil performance data

Full output data for the lower coil (solar coil) and the upper coil (boiler coil) rising water from 10C to 60C.

Hot Water production – showing lower coil ( normally solar coil ) and upper coil ( normally boiler coil ) performance – add both together for total performance.

Full details on our twin coil cylinders are on page 17 of the following brochure, for the 300 to 1,500 Litre.

Enamelled Domestic hot water cylinders brochure from Flexiheat UK

We also do this twin coil cylinder range in stainless steel – thus no sacrificial or permanent anodes are required – which cuts down on maintenance. The performance of the coils is also slightly better than our enamelled range. This range is designated the GX -M2

Stainless steel twin coil cylinder range data

Please see page 25 for general data and pages 28 and 29 for their twin coil hot water performance figures on the following brochure-

Stainless Steel cylinders for domestic hot water production and storage brochure Flexiheat UK

For our 1,500 to 6,000 Litres duplex stainless steel multi coil hot water cylinder range please see page 42 of the above

Dual coil cylinders from 1,500 to 6,000 Litres – our MVV -S2B / SS2B range

Technical data for the larger twin coil hot water cylinders

Twin coil vented cylinder

As standard, our twin coil tanks come as a “twin coil vented cylinder”, which means that as the water heats up and cools down within the cylinder, the vent pipe enables the water in the tank to expand and contract.

It is also a safety system that lets water expand and flow into the expansion tank if the water heater gets too hot. Vented twin coil cylinders can be ideal for retro fit applications where no pipework changes are necessary.

Twin coil hot water solar cylinders

These twin coil hot water cylinders can also be used as a twin solar cylinder, whereby both coils can be connected to solar panels or a solar system, rather than a gas or oil fired boiler suitable for the upper coil. Solar cylinders are leading the way in low-carbon or zero carbon hot water systems as the water heated is via the sun’s energy.So, if you have solar panels, you can if so, desired use these as twin coil solar cylinders, with each coil being a solar coil as such.

Twin coil unvented cylinder

These days, an unvented hot system is the most popular in the UK, as they take the mains water pressure directly to be heated.

This kind of twin-coil unvented cylinder is directly supplied with water from the mains. Mains water enters the bottom of the cylinder directly, eliminating the need for a tank in the loft.

The benefit of using this kind of cylinder is that the water will be supplied under mains pressure, which is very typical in most UK properties these days, so there will be no hot water pressure problems.

Our dual coil hot water cylinder range can be made unvented, by the simple installation of an unvented kit on the unit.

Contact us

Should you require anymore assistance, information, check stock, or get prices on the best twin coil cylinder range on the UK market, please don’t hesitate to contact our customer service sales team on 01202 822221 or use our e mail contact above on the web page for our email form.