Baxi 24 Litre Buffer Vessel
The Baxi 24 Litre Buffer Vessel (MPN 7851676) is a factory-insulated thermal storage tank engineered to sit between your Baxi air source heat pump and the central heating circuit. By adding essential system volume, the buffer prevents the compressor from short-cycling on low water-content systems, ensures the heat pump has the energy reserve it needs for reliable cold-weather defrost cycles, and decouples the pump's steady flow from the variable demand of thermostatic radiator valves and zoned underfloor circuits. The result is lower compressor wear, a better seasonal COP, and a quieter, more stable system — all from a compact unit that hangs from the wall and connects with standard G 1¼" fittings. At 24 litres nominal capacity (23 L measured), it meets the Baxi minimum system-volume requirement for the 4 kW, 5 kW, 7 kW and 8 kW HP40 and HP50 monobloc heat pumps and is rated Energy Class A with a standing loss of just 21 W.
This buffer vessel must be installed by a competent and qualified heating engineer in accordance with current Building Regulations, BS 7074:1, and EN 12828. The vessel must be protected from freezing and must not be used for potable or domestic hot water storage.
The 24 L buffer is sized for Baxi HP40 and HP50 monobloc heat pumps (4–8 kW outputs) where the Baxi installation manual specifies a minimum system volume of >25 L. For 11 kW and 13 kW heat pumps, or cascade installations, the Baxi 40 L Buffer Vessel is required instead. Always calculate total system volume including pipework and emitters before specifying.
Low water-content heating systems — particularly those with many thermostatic radiator valves — offer the heat pump little thermal mass to work against. The 24 L buffer adds the system volume the compressor needs to run in sustained, efficient cycles rather than starting and stopping repeatedly. Fewer compressor starts means less wear, lower noise, and a longer service life for the heat pump.
When outdoor temperatures drop, the heat pump must periodically defrost its outdoor coil. The buffer stores enough thermal energy to sustain flow to the radiators or underfloor circuits during the defrost cycle, preventing occupants from experiencing a cold drop in temperature. This is particularly important in the UK climate where overnight temperatures regularly trigger defrost events.
In some system layouts, the buffer vessel provides a hydraulic separation point between the heat pump's primary circuit and the distribution circuit. This protects the heat pump from pressure spikes caused by multiple zone valves closing simultaneously, and allows the primary and secondary circuits to operate at different flow rates — critical for zoned systems with mixed radiator and underfloor heating circuits.
The vessel's 63.5 mm rigid polyurethane foam shell keeps standing losses to just 21 W, earning it an Energy Class A rating under EU Regulation 812/2013. Heat stored in the buffer is retained efficiently between heat pump cycles, reducing the frequency of top-up heating and contributing to a better seasonal efficiency figure for the whole system.
With a maximum working pressure of 10 bar and a maximum temperature rating of 95 °C, the vessel comfortably exceeds the operating parameters of current Baxi heat pumps. It complies with the Pressure Equipment Directive 2014/68/EU and EN 12897:2020 Appendix B, giving installers confidence in long-term performance and regulatory compliance.
The buffer ships with wall-mounting brackets and a thermometer as standard. Connections include G 1¼" flow, return, heater, and auxiliary ports plus three G ½" sensor pockets, a G ½" thermometer port, and a G ½" drain — giving installers the flexibility to add immersion backup heating, temperature sensors, and service connections without additional fittings. Unused ports ship with plug and gasket kits included.
| MPN | 7851676 |
| Nominal Capacity | 24 L (measured: 23 L) |
| Maximum Working Pressure | 10 bar |
| Maximum Working Temperature | 95 °C |
| Standing Loss | 21 W |
| Energy Class | A |
| Insulation Material | Rigid polyurethane foam (PU) |
| Insulation Thickness | 63.5 mm |
| Empty Weight | 9 kg |
| Air Vent Connection | G 1¼" |
| Heater Inlet / Outlet | G 1¼" |
| Auxiliary Connection | G 1¼" |
| Thermometer Port | G ½" |
| Sensor Pockets | 3 × G ½" |
| Drain Connection | G ½" |
| Immersion Heater Port | 1½" BSP (plug and gasket supplied) |
| Mounting | Wall-hung (brackets supplied) |
| Compatible Heat Pumps | Baxi HP40 & HP50 monobloc ASHP (4–8 kW) |
| Warranty | 12 months parts and labour |
| Directives | 2009/125/EC (ErP), 2014/68/EU (PED), EU 812/2013, EU 814/2013, EN 12897:2020 App B |
- 1 × Baxi 24 L Buffer Vessel with wall-mounting brackets and thermometer pre-fitted
- 1 × 1½" immersion heater plug & gasket (caps the immersion port if no backup heater is fitted)
- 3 × ½" sensor pocket plugs (caps unused sensor pockets)
- 1 × Energy label
- 1 × Installation and Maintenance manual
Do I need a buffer vessel with my Baxi heat pump?
Is the 24 L vessel the right size for my heat pump?
Can I use this buffer vessel with a non-Baxi heat pump?
Can the buffer vessel be used to store domestic hot water?
Does the buffer vessel include an immersion heater?
What is the warranty on the Baxi 24 L Buffer Vessel?
Original: $539.87
-65%$539.87
$188.95Baxi 24 Litre Buffer Vessel
The Baxi 24 Litre Buffer Vessel (MPN 7851676) is a factory-insulated thermal storage tank engineered to sit between your Baxi air source heat pump and the central heating circuit. By adding essential system volume, the buffer prevents the compressor from short-cycling on low water-content systems, ensures the heat pump has the energy reserve it needs for reliable cold-weather defrost cycles, and decouples the pump's steady flow from the variable demand of thermostatic radiator valves and zoned underfloor circuits. The result is lower compressor wear, a better seasonal COP, and a quieter, more stable system — all from a compact unit that hangs from the wall and connects with standard G 1¼" fittings. At 24 litres nominal capacity (23 L measured), it meets the Baxi minimum system-volume requirement for the 4 kW, 5 kW, 7 kW and 8 kW HP40 and HP50 monobloc heat pumps and is rated Energy Class A with a standing loss of just 21 W.
This buffer vessel must be installed by a competent and qualified heating engineer in accordance with current Building Regulations, BS 7074:1, and EN 12828. The vessel must be protected from freezing and must not be used for potable or domestic hot water storage.
The 24 L buffer is sized for Baxi HP40 and HP50 monobloc heat pumps (4–8 kW outputs) where the Baxi installation manual specifies a minimum system volume of >25 L. For 11 kW and 13 kW heat pumps, or cascade installations, the Baxi 40 L Buffer Vessel is required instead. Always calculate total system volume including pipework and emitters before specifying.
Low water-content heating systems — particularly those with many thermostatic radiator valves — offer the heat pump little thermal mass to work against. The 24 L buffer adds the system volume the compressor needs to run in sustained, efficient cycles rather than starting and stopping repeatedly. Fewer compressor starts means less wear, lower noise, and a longer service life for the heat pump.
When outdoor temperatures drop, the heat pump must periodically defrost its outdoor coil. The buffer stores enough thermal energy to sustain flow to the radiators or underfloor circuits during the defrost cycle, preventing occupants from experiencing a cold drop in temperature. This is particularly important in the UK climate where overnight temperatures regularly trigger defrost events.
In some system layouts, the buffer vessel provides a hydraulic separation point between the heat pump's primary circuit and the distribution circuit. This protects the heat pump from pressure spikes caused by multiple zone valves closing simultaneously, and allows the primary and secondary circuits to operate at different flow rates — critical for zoned systems with mixed radiator and underfloor heating circuits.
The vessel's 63.5 mm rigid polyurethane foam shell keeps standing losses to just 21 W, earning it an Energy Class A rating under EU Regulation 812/2013. Heat stored in the buffer is retained efficiently between heat pump cycles, reducing the frequency of top-up heating and contributing to a better seasonal efficiency figure for the whole system.
With a maximum working pressure of 10 bar and a maximum temperature rating of 95 °C, the vessel comfortably exceeds the operating parameters of current Baxi heat pumps. It complies with the Pressure Equipment Directive 2014/68/EU and EN 12897:2020 Appendix B, giving installers confidence in long-term performance and regulatory compliance.
The buffer ships with wall-mounting brackets and a thermometer as standard. Connections include G 1¼" flow, return, heater, and auxiliary ports plus three G ½" sensor pockets, a G ½" thermometer port, and a G ½" drain — giving installers the flexibility to add immersion backup heating, temperature sensors, and service connections without additional fittings. Unused ports ship with plug and gasket kits included.
| MPN | 7851676 |
| Nominal Capacity | 24 L (measured: 23 L) |
| Maximum Working Pressure | 10 bar |
| Maximum Working Temperature | 95 °C |
| Standing Loss | 21 W |
| Energy Class | A |
| Insulation Material | Rigid polyurethane foam (PU) |
| Insulation Thickness | 63.5 mm |
| Empty Weight | 9 kg |
| Air Vent Connection | G 1¼" |
| Heater Inlet / Outlet | G 1¼" |
| Auxiliary Connection | G 1¼" |
| Thermometer Port | G ½" |
| Sensor Pockets | 3 × G ½" |
| Drain Connection | G ½" |
| Immersion Heater Port | 1½" BSP (plug and gasket supplied) |
| Mounting | Wall-hung (brackets supplied) |
| Compatible Heat Pumps | Baxi HP40 & HP50 monobloc ASHP (4–8 kW) |
| Warranty | 12 months parts and labour |
| Directives | 2009/125/EC (ErP), 2014/68/EU (PED), EU 812/2013, EU 814/2013, EN 12897:2020 App B |
- 1 × Baxi 24 L Buffer Vessel with wall-mounting brackets and thermometer pre-fitted
- 1 × 1½" immersion heater plug & gasket (caps the immersion port if no backup heater is fitted)
- 3 × ½" sensor pocket plugs (caps unused sensor pockets)
- 1 × Energy label
- 1 × Installation and Maintenance manual
Do I need a buffer vessel with my Baxi heat pump?
Is the 24 L vessel the right size for my heat pump?
Can I use this buffer vessel with a non-Baxi heat pump?
Can the buffer vessel be used to store domestic hot water?
Does the buffer vessel include an immersion heater?
What is the warranty on the Baxi 24 L Buffer Vessel?
Product Information
Product Information
Shipping & Returns
Shipping & Returns
Description
The Baxi 24 Litre Buffer Vessel (MPN 7851676) is a factory-insulated thermal storage tank engineered to sit between your Baxi air source heat pump and the central heating circuit. By adding essential system volume, the buffer prevents the compressor from short-cycling on low water-content systems, ensures the heat pump has the energy reserve it needs for reliable cold-weather defrost cycles, and decouples the pump's steady flow from the variable demand of thermostatic radiator valves and zoned underfloor circuits. The result is lower compressor wear, a better seasonal COP, and a quieter, more stable system — all from a compact unit that hangs from the wall and connects with standard G 1¼" fittings. At 24 litres nominal capacity (23 L measured), it meets the Baxi minimum system-volume requirement for the 4 kW, 5 kW, 7 kW and 8 kW HP40 and HP50 monobloc heat pumps and is rated Energy Class A with a standing loss of just 21 W.
This buffer vessel must be installed by a competent and qualified heating engineer in accordance with current Building Regulations, BS 7074:1, and EN 12828. The vessel must be protected from freezing and must not be used for potable or domestic hot water storage.
The 24 L buffer is sized for Baxi HP40 and HP50 monobloc heat pumps (4–8 kW outputs) where the Baxi installation manual specifies a minimum system volume of >25 L. For 11 kW and 13 kW heat pumps, or cascade installations, the Baxi 40 L Buffer Vessel is required instead. Always calculate total system volume including pipework and emitters before specifying.
Low water-content heating systems — particularly those with many thermostatic radiator valves — offer the heat pump little thermal mass to work against. The 24 L buffer adds the system volume the compressor needs to run in sustained, efficient cycles rather than starting and stopping repeatedly. Fewer compressor starts means less wear, lower noise, and a longer service life for the heat pump.
When outdoor temperatures drop, the heat pump must periodically defrost its outdoor coil. The buffer stores enough thermal energy to sustain flow to the radiators or underfloor circuits during the defrost cycle, preventing occupants from experiencing a cold drop in temperature. This is particularly important in the UK climate where overnight temperatures regularly trigger defrost events.
In some system layouts, the buffer vessel provides a hydraulic separation point between the heat pump's primary circuit and the distribution circuit. This protects the heat pump from pressure spikes caused by multiple zone valves closing simultaneously, and allows the primary and secondary circuits to operate at different flow rates — critical for zoned systems with mixed radiator and underfloor heating circuits.
The vessel's 63.5 mm rigid polyurethane foam shell keeps standing losses to just 21 W, earning it an Energy Class A rating under EU Regulation 812/2013. Heat stored in the buffer is retained efficiently between heat pump cycles, reducing the frequency of top-up heating and contributing to a better seasonal efficiency figure for the whole system.
With a maximum working pressure of 10 bar and a maximum temperature rating of 95 °C, the vessel comfortably exceeds the operating parameters of current Baxi heat pumps. It complies with the Pressure Equipment Directive 2014/68/EU and EN 12897:2020 Appendix B, giving installers confidence in long-term performance and regulatory compliance.
The buffer ships with wall-mounting brackets and a thermometer as standard. Connections include G 1¼" flow, return, heater, and auxiliary ports plus three G ½" sensor pockets, a G ½" thermometer port, and a G ½" drain — giving installers the flexibility to add immersion backup heating, temperature sensors, and service connections without additional fittings. Unused ports ship with plug and gasket kits included.
| MPN | 7851676 |
| Nominal Capacity | 24 L (measured: 23 L) |
| Maximum Working Pressure | 10 bar |
| Maximum Working Temperature | 95 °C |
| Standing Loss | 21 W |
| Energy Class | A |
| Insulation Material | Rigid polyurethane foam (PU) |
| Insulation Thickness | 63.5 mm |
| Empty Weight | 9 kg |
| Air Vent Connection | G 1¼" |
| Heater Inlet / Outlet | G 1¼" |
| Auxiliary Connection | G 1¼" |
| Thermometer Port | G ½" |
| Sensor Pockets | 3 × G ½" |
| Drain Connection | G ½" |
| Immersion Heater Port | 1½" BSP (plug and gasket supplied) |
| Mounting | Wall-hung (brackets supplied) |
| Compatible Heat Pumps | Baxi HP40 & HP50 monobloc ASHP (4–8 kW) |
| Warranty | 12 months parts and labour |
| Directives | 2009/125/EC (ErP), 2014/68/EU (PED), EU 812/2013, EU 814/2013, EN 12897:2020 App B |
- 1 × Baxi 24 L Buffer Vessel with wall-mounting brackets and thermometer pre-fitted
- 1 × 1½" immersion heater plug & gasket (caps the immersion port if no backup heater is fitted)
- 3 × ½" sensor pocket plugs (caps unused sensor pockets)
- 1 × Energy label
- 1 × Installation and Maintenance manual
