Baxi 40L Buffer Vessel for Air Source Heat Pumps
The Baxi 40 Litre Buffer Vessel (MPN 7768655) is a thermal storage tank designed to sit between a Baxi air source heat pump and the heating circuit, providing the system volume needed for reliable defrost cycles and smoothing flow temperature across the home. At 40 litres, this is the variant Baxi specifies for the 11 kW and 13 kW Baxi monobloc heat pumps, where the installation manual mandates a buffer of greater than 40 L.
A correctly sized buffer is one of the simplest ways to increase the seasonal efficiency of a heat pump installation. It reduces compressor short-cycling, gives the unit the energy reserve it needs to defrost cleanly in cold weather, and decouples the heat pump's flow demand from the variable demand of thermostatic radiator valves and zoned underfloor circuits.
Key features
Sized for 11–13 kW heat pumps
Meets Baxi's published >40 L minimum buffer requirement for the 11 kW and 13 kW monobloc heat pumps — the simplest off-the-shelf solution for these units.
Reliable defrost performance
Stored thermal energy provides the volume the heat pump draws on during a defrost cycle, so radiators stay warm and the cycle completes cleanly.
Reduces short-cycling
Dampens the swing between flow and return temperatures, allowing the inverter compressor to modulate smoothly rather than starting and stopping — extending equipment life and reducing energy use.
Volumiser or 4-port buffer
Flexible plumbing — install as a simple in-line volumiser (two ports) or as a fully decoupled 4-port buffer between primary and secondary circuits.
Generous 1¼" connections
1 ¼" inlet and outlet connection sizes match the typical pipework for larger ASHPs and keep pressure drop low across the buffer.
A-rated insulation
A energy rating with thick foam insulation — minimal standby losses keep the stored heat where it is needed, in the system.
Technical specifications
| Manufacturer | Baxi |
| Manufacturer part number (MPN) | 7768655 |
| Product family | Baxi air source heat pump accessories |
| Capacity | 40 litres |
| Inlet / outlet connections | 1¼" BSP |
| Energy rating | A |
| Maximum working pressure | 3 bar |
| Maximum operating temperature | 95 °C |
| Minimum operating temperature | 6 °C |
| Configuration | Volumiser or 4-port buffer vessel |
| Application | Baxi 11–13 kW monobloc ASHPs and cascade systems |
| Warranty | 2 years, parts only |
Frequently asked questions
Why do I need a buffer vessel with a heat pump?
Will the 40L work with my heat pump?
Can I use it as a 2-port volumiser, or do I have to plumb it as a 4-port buffer?
What about insulation losses?
Does it come with a warranty?
Original: $1,064.89
-65%$1,064.89
$372.71Baxi 40L Buffer Vessel for Air Source Heat Pumps
The Baxi 40 Litre Buffer Vessel (MPN 7768655) is a thermal storage tank designed to sit between a Baxi air source heat pump and the heating circuit, providing the system volume needed for reliable defrost cycles and smoothing flow temperature across the home. At 40 litres, this is the variant Baxi specifies for the 11 kW and 13 kW Baxi monobloc heat pumps, where the installation manual mandates a buffer of greater than 40 L.
A correctly sized buffer is one of the simplest ways to increase the seasonal efficiency of a heat pump installation. It reduces compressor short-cycling, gives the unit the energy reserve it needs to defrost cleanly in cold weather, and decouples the heat pump's flow demand from the variable demand of thermostatic radiator valves and zoned underfloor circuits.
Key features
Sized for 11–13 kW heat pumps
Meets Baxi's published >40 L minimum buffer requirement for the 11 kW and 13 kW monobloc heat pumps — the simplest off-the-shelf solution for these units.
Reliable defrost performance
Stored thermal energy provides the volume the heat pump draws on during a defrost cycle, so radiators stay warm and the cycle completes cleanly.
Reduces short-cycling
Dampens the swing between flow and return temperatures, allowing the inverter compressor to modulate smoothly rather than starting and stopping — extending equipment life and reducing energy use.
Volumiser or 4-port buffer
Flexible plumbing — install as a simple in-line volumiser (two ports) or as a fully decoupled 4-port buffer between primary and secondary circuits.
Generous 1¼" connections
1 ¼" inlet and outlet connection sizes match the typical pipework for larger ASHPs and keep pressure drop low across the buffer.
A-rated insulation
A energy rating with thick foam insulation — minimal standby losses keep the stored heat where it is needed, in the system.
Technical specifications
| Manufacturer | Baxi |
| Manufacturer part number (MPN) | 7768655 |
| Product family | Baxi air source heat pump accessories |
| Capacity | 40 litres |
| Inlet / outlet connections | 1¼" BSP |
| Energy rating | A |
| Maximum working pressure | 3 bar |
| Maximum operating temperature | 95 °C |
| Minimum operating temperature | 6 °C |
| Configuration | Volumiser or 4-port buffer vessel |
| Application | Baxi 11–13 kW monobloc ASHPs and cascade systems |
| Warranty | 2 years, parts only |
Frequently asked questions
Why do I need a buffer vessel with a heat pump?
Will the 40L work with my heat pump?
Can I use it as a 2-port volumiser, or do I have to plumb it as a 4-port buffer?
What about insulation losses?
Does it come with a warranty?
Product Information
Product Information
Shipping & Returns
Shipping & Returns
Description
The Baxi 40 Litre Buffer Vessel (MPN 7768655) is a thermal storage tank designed to sit between a Baxi air source heat pump and the heating circuit, providing the system volume needed for reliable defrost cycles and smoothing flow temperature across the home. At 40 litres, this is the variant Baxi specifies for the 11 kW and 13 kW Baxi monobloc heat pumps, where the installation manual mandates a buffer of greater than 40 L.
A correctly sized buffer is one of the simplest ways to increase the seasonal efficiency of a heat pump installation. It reduces compressor short-cycling, gives the unit the energy reserve it needs to defrost cleanly in cold weather, and decouples the heat pump's flow demand from the variable demand of thermostatic radiator valves and zoned underfloor circuits.
Key features
Sized for 11–13 kW heat pumps
Meets Baxi's published >40 L minimum buffer requirement for the 11 kW and 13 kW monobloc heat pumps — the simplest off-the-shelf solution for these units.
Reliable defrost performance
Stored thermal energy provides the volume the heat pump draws on during a defrost cycle, so radiators stay warm and the cycle completes cleanly.
Reduces short-cycling
Dampens the swing between flow and return temperatures, allowing the inverter compressor to modulate smoothly rather than starting and stopping — extending equipment life and reducing energy use.
Volumiser or 4-port buffer
Flexible plumbing — install as a simple in-line volumiser (two ports) or as a fully decoupled 4-port buffer between primary and secondary circuits.
Generous 1¼" connections
1 ¼" inlet and outlet connection sizes match the typical pipework for larger ASHPs and keep pressure drop low across the buffer.
A-rated insulation
A energy rating with thick foam insulation — minimal standby losses keep the stored heat where it is needed, in the system.
Technical specifications
| Manufacturer | Baxi |
| Manufacturer part number (MPN) | 7768655 |
| Product family | Baxi air source heat pump accessories |
| Capacity | 40 litres |
| Inlet / outlet connections | 1¼" BSP |
| Energy rating | A |
| Maximum working pressure | 3 bar |
| Maximum operating temperature | 95 °C |
| Minimum operating temperature | 6 °C |
| Configuration | Volumiser or 4-port buffer vessel |
| Application | Baxi 11–13 kW monobloc ASHPs and cascade systems |
| Warranty | 2 years, parts only |
