The Zilmet Zil-B Insulated Buffer Tank adds extra water volume to a sealed heating circuit and works as a hydraulic separator between primary and secondary circuits — a common requirement for heat pump systems that need a minimum system volume to run efficiently. Available in 25L, 50L, 80L, and 100L capacities, every size in the range shares the same build: a mild steel vessel wrapped in 41mm premium polyurethane foam insulation to minimise standing heat loss, rated to 4 bar maximum operating pressure and 95°C maximum inlet temperature, with tolerance for a glycol mix of up to 50% for frost-protected or antifreeze-dosed systems.
By decoupling the heat pump's primary flow from the secondary heating circuit, the buffer tank eliminates compressor short-cycling — the rapid on/off switching that shortens compressor life and wastes energy when a heat pump is paired with a low-volume circuit or zoned system. Every size ships with mounting brackets for wall or floor installation, so the tank can be fitted to suit the plant room layout without extra bracketry.
4 Bar
Max. operating pressure
95°C
Max. inlet temperature
Steel
Mild steel construction
Sizing guide: the 25L and 50L tanks suit single dwellings and smaller heat pump installations where hydraulic separation is the main requirement; the 80L and 100L tanks suit larger properties or systems with multiple heating zones that need greater buffer volume to avoid short-cycling.
Connections vary by size: the 25L and 50L tanks use 1" and ¾" BSP connections, while the 80L and 100L step up to 1¼" BSP throughout. Check the variant table below and confirm against existing pipework before ordering.
Hydraulic Separation
Decouples the heat pump's primary circuit from the secondary heating circuit, protecting flow rates and preventing pressure interactions between the two.
Stops Short-Cycling
Adds system volume so the compressor runs longer cycles rather than switching rapidly on and off, extending compressor lifespan and improving efficiency.
Premium Foam Insulation
41mm of polyurethane foam insulation minimises standing heat loss from stored water, keeping the buffered volume at temperature for longer.
Glycol Compatible
Tolerates a glycol mix of up to 50%, making it suitable for frost-protected systems and exposed or unheated plant room locations.
Wall or Floor Mounting
Supplied with mounting brackets for either wall-hung or floor-standing installation, giving flexibility to fit the available plant room space.
Vent and Drain Ready
Dedicated top and bottom connections allow straightforward venting during commissioning and full draining for maintenance or system changes.
Variant Specifications
Connections
C1: 1", C2: ¾"
C1: 1", C2: ¾"
C1/C2: 1¼"
C1/C2: 1¼"
Height
925mm
1008mm
891mm
1071mm
Length
480mm
580mm
365mm
545mm
Diameter
290mm
360mm
469mm
469mm
Weight
Not published
15kg
Not published
Not published
MPN
BUFF25 / 16B0002500
BUFF50 / 16B0005000
BUFF80 / 16B0008000
BUFF100 / 16B0001000
EAN
Not published
655390526267
655390529114
Not published
Specifications Common to All Sizes
Function
Buffer vessel and hydraulic separator
Insulation
41mm polyurethane foam
Max. operating pressure
4 bar
Max. inlet temperature
95°C
Glycol compatibility
Up to 50% mix
Mounting
Wall or floor, brackets supplied
What size buffer tank do I need?
Sizing depends on the heat pump's minimum system volume requirement and the property's heating zones — check the heat pump manufacturer's specification for the minimum water volume needed, then choose the tank size that brings the total system volume above that threshold. Larger systems with multiple zones typically need the 80L or 100L options; smaller single-zone systems are often well served by the 25L or 50L tanks.
Why does a heat pump need a buffer tank?
Heat pumps run most efficiently with longer, steadier compressor cycles. A low-volume secondary circuit — especially with zone valves closing off flow — can cause the compressor to short-cycle, switching on and off rapidly. A buffer tank adds thermal mass and hydraulic separation to prevent this, protecting the compressor and improving overall efficiency.
Can this tank be used with a glycol/antifreeze mix?
Yes, the Zil-B tank is rated for a glycol mix of up to 50%, making it suitable for systems with frost protection or in unheated plant room locations where freezing is a risk.
Do the connections differ between sizes?
Yes. The 25L and 50L tanks use 1" and ¾" BSP connections, while the 80L and 100L tanks use 1¼" BSP connections throughout. Confirm the connection size against your existing pipework and any reducing fittings needed before ordering.
Is mounting hardware included?
Yes, every size in the range is supplied with mounting brackets suitable for wall-hung or floor-standing installation, so no additional bracketry needs to be sourced separately.
