Flexiheat UKLow height buffer tanks – 2,000 to 6,000 Litres
Buffer tanks or vessels with low height from Flexiheat UK
Low height buffer tanks or vessels are mainly about solving space and hydraulic layout problems without losing the core benefits of a buffer vessel.
The main advantages are the following:
They fit where standard height buffer tanks will not
That is the largest one. In plant rooms with low ceilings, loft spaces, or retrofit jobs, a squat buffer can be installed where a tall buffer simply cannot be. There is no standard floor-to-floor/storey height in commercial or industrial buildings; however, most data suggest that they are between 3.6 and 4.0 metres in height. Our tanks can comfortably fit within this height and allow easy and straightforward installation of the associated pipework and fittings.
They are easier to get into the building
A low height tank is often easier to move through doorways, around corners, and into basements or tight risers than a tall, awkward buffer tank.
They work well in retrofit plant rooms
When replacing older boilers or adding a heat pump, there is often limited vertical space because of existing pipework, flues, cable trays, or services above. A low height tank gives more freedom.
They can make pipework layout cleaner and easier
In some jobs, especially where headers and pumps are mounted at a low level, a horizontal or squat arrangement can reduce awkward vertical runs and help keep the cooling or heating system pipework compact.
They still provide the usual buffer-tank benefits
Even in a low-height format, they can still:
- Add system water volume for air source heat pumps, ground source heat pumps, biomass boilers or even chillers.
- Reduce short cycling of the heat pump system, chiller system or boiler system.
- Improve heat pump or boiler run times
- Help hydraulic separation for the heating system where it’s designed for it
- Improve defrost support on air source heat pump systems
- Stabilise flow in mixed circuits
They can help with service access above the vessel
A tall buffer tank can leave no room for top connections, air vents, or insulation clearance. A low tank can free up working space overhead.
That said, there are trade-offs.
A low-height buffer tank may have the following:
- A larger floor footprint
- Sightly less effective temperature stratification than a taller vessel
So in practice, the advantage is usually installation practicality first, then system performance benefits second.
For heating engineers, the usual reason to choose one is the following:
“I need buffer volume, but I do not have the headroom for a standard vertical buffer tank or vessel.“
Low height buffer vessel/tank product range options
All these buffer tanks in this range come with 5 x ½” tappings or ports for temperature sensors or other sensors, arranged vertically up the tank. They also have a 2 x ½” tapping’s for a pressure gauge and thermometer gauge and a 1 ¼” drain point at the bottom of the tank. Finally, on the top area of the buffer, they have a 1¼” port for a pressure relief safety valve, a 1” port for an automatic air vent and a 1” port for an anti-vacuum valve to be installed.
They also benefit from a 480 mm (400 mm effective opening) inspection or cleanout flange for easy maintenance and inspection of the buffer tank, as well as lifting eyes on the top and on the side of the tank.
Low-height buffer vessels or tanks from 2,000 to 5,000 litres
Overall dimensions of the range
Buffer tank or vessel with low-height dimensions table from Flexiheat UK
Firstly, our heating hot water only buffer tanks range from 2,000 to 6,000 litres in capacity. The 2,000 to 3,000 litre tanks have 100 mm (4″) PN6 flanged inlet and outlet connections, while the 4,000 and 5,000 litre tanks have 150 mm (6″) PN6 flanged inlet and outlet connections, and the 6,000 litres have 200mm (8″) connections.
| Code |
Product description – Heating only – 100 mm polyester fibre insulation |
| FHPSLH2000-H | 2000 Litre PS LH Carbon steel buffer tank – 4 x 4″ PN6 flanged connections, 5 temp sensors & 480/400mm inspection port/flange |
| FHPSLH2500-H | 2500 Litre PS LH Carbon steel buffer tank – 4 x 4″ PN6 flanged connections, 5 temp sensors & 480/400mm inspection port/flange |
| FHPSLH3000-H | 3000 Litre PS LH Carbon steel buffer tank – 4 x 4″ PN6 flanged connections, 5 temp sensors & 480/400mm inspection port/flange |
| FHPSLH4000-H | 4000 Litre PS LH Carbon steel buffer tank – 4 x 6″ PN6 flanged connections, 5 temp sensors & 480/400mm inspection port/flange |
| FHPSLH5000-H | 5000 Litre PS LH Carbon steel buffer tank – 4 x 6″ PN6 flanged connections, 5 temp sensors & 480/400mm inspection port/flange |
| FHPSLH6000-H | 6000 Litre PS LH Carbon steel buffer tank – 4 x 8″ PN6 flanged connections, 5 temp sensors & 480/400mm inspection port/flange |
Then we have our dual-purpose buffer vessels/tanks for reversible operation heat pumps that can produce both heating and chilled water services
Chilled and/or heating system buffer tank option
| Code | Heating and Chilled or just Chilled only – 80 mm polyester fibre with 20 mm Armaflex | ||||||
| FHPSLH2000HC | 2000 Ltr PS LH Carbon steel buffer tank – 4 x 4″ PN6 flanged connections, 5 temp sensors & 480/400mm inspection port/flange | ||||||
| FHPSLH2500HC | 2500 Ltr PS LH Carbon steel buffer tank – 4 x 4″ PN6 flanged connections, 5 temp sensors & 480/400mm inspection port/flange | ||||||
| FHPSLH3000HC | 3000 Ltr PS LH Carbon steel buffer tank – 4 x 4″ PN6 flanged connections, 5 temp sensors & 480/400mm inspection port/flange | ||||||
| FHPSLH4000HC | 4000 Ltr PS LH Carbon steel buffer tank – 4 x 6″ PN6 flanged connections, 5 temp sensors & 480/400mm inspection port/flange | ||||||
| FHPSLH5000HC | 5000 Ltr PS LH Carbon steel buffer tank – 4 x 6″ PN6 flanged connections, 5 temp sensors & 480/400mm inspection port/flange | ||||||
| FHPSLH6000HC | 6000 Ltr PS LH Carbon steel buffer tank – 4 x 8″ PN6 flanged connections, 5 temp sensors & 480/400mm inspection port/flange | ||||||
Download the drawing here.
Buffer tank / vessel options
On request, we can add the following options to the buffer:
They are used when a buffer tank needs better control of flow, better temperature layering, or improved separation between heating circuits.
Baffle plates, sparge pipes, water diffusers, and perforated diffuser plate options we can fit to our buffer tanks and vessels from Flexiheat UK
1 to 3 – Various connection configurations, 2 ports, 4 ports flanged, screwed, etc.
4 – Vertical baffle plate / deflector plate – Slows and redirects incoming water, reducing short-circuiting between flow and return connections.
5 – Internal diffuser pipes / sparge pipes – Horizontal internal pipes that spread water gently across the vessel instead of firing it straight in at high velocity. Helps reduce mixing.
6 – Perforated diffuser plate / baffle plate – A plate with holes that disperses water flow evenly through the tank. This is useful where flow needs to be slowed and spread.
7 – Sparge pipes / internal diffuser pipe – The sparge pipe spreads the flow through a series of holes or slots, rather than allowing water to enter the vessel through a single open connection and blast straight across the tank.
8 – Stratification baffle plates – Horizontal plates that help maintain temperature layers inside the buffer tank, reducing unwanted mixing between hotter and cooler water.
8a – Advanced stratification baffle arrangement – An improved version of internal baffles that guides flow and keeps thermal layering more effective.
9 – Water diffuser – A plate with holes that disperses water flow evenly through the tank. This feature is useful where flow needs to be slowed and spread.
Stainless steel buffer tank option
As an option, we can manufacture this range of low-height buffer tanks in stainless steel. A 304 stainless steel buffer tank offers several advantages over a conventional carbon-steel vessel, particularly where corrosion resistance, cleanliness and long service life are important.
The main benefit is improved resistance to corrosion. Stainless steel contains chromium, which forms a protective surface layer that helps prevent rusting. This makes a 304 stainless steel buffer tank less dependent on internal coatings, sacrificial anodes or corrosion inhibitors than many mild-steel alternatives.
Because there is no painted or raw surface to deteriorate, there is also less risk of coating failure, flaking or exposed steel corroding over time. Stainless steel manufactured buffers will reduce maintenance requirements and improve reliability, provided the system water quality is correctly controlled.
304 stainless steel is also hygienic and has a smooth internal surface. This limits the accumulation of corrosion debris, sludge, and loose scale within the vessel. Cleaner system water can help protect pumps, valves, heat exchangers (vital in heat pump systems), and control components.
However, 304 stainless steel is not completely corrosion-proof. High chloride levels, unsuitable chemicals, poor welding or contact with dissimilar metals can cause localised corrosion. Correct water treatment, electrical bonding, insulation and installation practices remain essential.
Buffer vessel insulation
Heating buffer option – usually used on air source heat pumps but also biomass boilers
The 100 mm polyester-fibre thermal insulation, a highly efficient insulation, ensures a high capacity for heat conservation and minimises temperature fluctuations in the water within the tank, which leads to fewer start-ups of the connected heat sources (usually heat pump systems – air-source heat pumps or ground-source heat pump systems – but also suitable biomass heating systems), resulting in significant benefits regarding operating expenses and extending their lifespan.
Chilled water and heating option
The chilled water and heating option has anti-condensation insulation, with 20 mm Armaflex lagging and 80 mm polyester fibre, providing a total of 100 mm of insulation.
Chilled water tanks operate well below ambient air temperature, making them highly susceptible to “sweating”. Armaflex’s closed-cell structure builds a vapour barrier cell by cell. This system stops moisture from penetrating or accumulating on the tank wall, helping to prevent mould growth and structural damage.
Domestic hot water option
We can manufacture these buffer tanks in 316 stainless steel for domestic hot water storage applications, on request.
Contact Flexiheat UK
For more detailed information on stock availability, delivery times, price or ordering our low height buffer tank range, the perfect solution for height-restricted areas in commercial buildings with cooling or heating systems that require a buffer tank for air source heat pumps, biomass boiler heat sources or chilled water systems.
Please contact our sales team at 01202 822221 or use our website’s email contact form to discuss your requirements.
Flexiheat UK
Flexiheat UK