Buffer tank with coil or twin coils

Buffer tank with coil or twin coils

A buffer tank with coil or coils is used to hydraulically separate a heat source or sources, in the event of a twin coil buffer tank, from the heating system’s hot water. This can be required for mechanical engineering reasons such as flow rate or temperature difference between the heating system and the heating source , which is often the case with heat pump heating systems, be they air source heat pumps or geothermal heating systems.

With a full range of buffer tanks from 260 litres in hot water storage volume all the way up to 5,000 litres of storage capacity, we have the volumes to satisfy any application or performance requirements for your inertia tank.

We do two ranges which will detail below

Why use a buffer with a coil ?

The coil acts as a heat exchanger, separating the hot water generated from a heat pump, boiler, or solar thermal fluid in the event of a solar thermal system from the hot heating water in the thermal storage tanks.

This can ensure that there are no problems with flow rates between the heated water from the heat source and the heating system, and also temperature differences, i.e., some solar system fluids can get up to 200 °C, whereas the storage tank temperature ratings are either 95 °C or 110 °C maximum. Thus, the use of a heat exchanger coil within the buffer tank is required.

The coils used are not a stainless steel coil , like those used in an indirect water heater that produces domestic hot water. We are not producing domestic hot water in a buffer tank with an intermediate heating coil to produce hot water for the heating system. The coils are made of steel, just like the thermal storage tanks.

Which means these buffer tanks must be used on a sealed heating system only, and the heating water must be treated with a corrosion inhibitor.

Domestic hot water production

If you want a Buffer tank with a stainless steel coil to produce domestic hot water, then these are called Thermal store hot water cylinders or Thermal store cylinders – and we go into more detail on this range here: https://www.flexiheatuk.com/product/thermal-store-cylinders/ as these are our units for instantaneous domestic hot water heating or production via a stainless steel coil within the thermal storage tank and are available in volumes from 500 litres of storage to 2000 litres in range or size.

Single heat exchanger models

The first range is the “G” range. These are rated

Maximum working pressure: Coil – 25 Bar – Tank 6 bar

Maximum working temperature: Coil – 200 ºC – Tank 110 ºC

Single coil buffer tanks the G-IF or G-IFS range 260 litres to 1500 litres that are thermal stores to accommodate peak loads for the heating system, using an intermediate coil to hydraulically separate the heat source from the heating system water in a hot water cylinder from Flexiheat UK

The storage tank also has an immersion heater port, should you wish to install an immersion heater as a back up or top up heat source.


Technical data: The “G -IS” buffer tank range has larger tapping ports than the “G – IFS” buffer tank range, which has the standard 40mm (1-1/2″) See “EH” detail on the following:

G range of buffer tanks with single coil or heat exchanger detailing the hot water tapping detail on the buffer tank or thermal stores and heat exchanger detail Flexiheat UK

G-IS and G-IFS Buffer tank with a single coil / heat exchanger technical detail


Larger Size Storage Tank

Thermal storage tanks with hot water storage volumes ranging from 1,500 to 5,000 litres with a single coil.

These buffer tanks are available with an inspection and clean out manhole that is 400mm in diameter and are designated the “ISB” version.

Or as the standard unit without which is designated the “IS” version.

Buffer tanks with a single coil from 1500 litres to 5000 Litres in volume MV range Flexiheat UK


Technical detail

MV1500 to 5000 Litre buffer tanks with a single coil technical detail from Flexiheat UK

The full detail on the above tanks can be found in the following brochure – pages 12 & 13

Buffer Tanks Brochure Flexiheat UK


Solar thermal heating systems

Some fluids in the solar system can be heated to 200 °C. If this is the case, you need to use our “G” or “MV” range. However, if your water or fluid temperature is less than 110 °C, then we have another buffer tank product with a single coil, and these are detailed here:

Twin coil buffer tanks

Twin coil or two heat exchanger buffer tanks are suitable for applications with two energy heating systems feeding the thermal storage tanks. For example, one coil or heat exchanger can be fed by a thermal solar system, which is usually the lower coil in the buffer tank. The second coil or heat exchanger, which is located in the upper part of the buffer tank, can be fed by heat generated from either a traditional gas or oil boiler or heat pump heating systems, which can be either ground source heat pumps or air source heat pumps.

PPS2 Twin coil buffer tanks for sealed heating systems Flexiheat UK

Our Twin coil buffer tanks from 300 to 2,000 Litres in volume


These units are available from 300 to 2,000 litres in demand capacity.

The twin coil range has a heat exchanger maximum hot water temperature rating of 110 °C and 12 Bar pressure .

The buffer tank’s maximum temperature rating is 95 °C, and the pressure rating varies with the volume; please see the brochure for full details.

Flexiheat brochure for PPS2 Buffer tank with twin coils for sealed heating systems

Buffer tank with a coil or coils

Should you require more product information, availability, technical support, or prices on our complete range of buffer tanks with coil or coils then please don’t hesitate to get in touch. Contact our sales service team on 01202 822221 or use our email contact form via the contact tab above to message us.