{"product_id":"baxi-40l-buffer-vessel-for-air-source-heat-pumps","title":"Baxi 40L Buffer Vessel for Air Source Heat Pumps","description":"\u003cdiv style=\"font-size: 16px; line-height: 1.65; color: #2a2a2a; font-family: -apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,Helvetica,Arial,sans-serif; max-width: 900px; margin: 0 auto;\"\u003e\n\u003cp style=\"font-size: 1.05em; margin: 0 0 18px;\"\u003eThe \u003cstrong\u003eBaxi 40 Litre Buffer Vessel (MPN 7768655)\u003c\/strong\u003e is a thermal storage tank designed to sit between a Baxi air source heat pump and the heating circuit, providing the \u003cstrong\u003esystem volume needed for reliable defrost cycles\u003c\/strong\u003e and \u003cstrong\u003esmoothing flow temperature\u003c\/strong\u003e across the home. At 40 litres, this is the variant Baxi specifies for the \u003cstrong\u003e11 kW and 13 kW Baxi monobloc heat pumps\u003c\/strong\u003e, where the installation manual mandates a buffer of \u003cstrong\u003egreater than 40 L\u003c\/strong\u003e.\u003c\/p\u003e\n\u003cp style=\"margin: 0 0 22px;\"\u003eA correctly sized buffer is one of the simplest ways to \u003cstrong\u003eincrease the seasonal efficiency\u003c\/strong\u003e 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.\u003c\/p\u003e\n\u003cdiv style=\"display: grid; grid-template-columns: repeat(4,1fr); gap: 10px; margin: 0 0 28px;\"\u003e\n\u003cdiv style=\"background: #008377CF; color: #ffffff; padding: 18px 12px; border-radius: 8px; text-align: center;\"\u003e\n\u003cdiv style=\"font-size: 1.45em; font-weight: bold; line-height: 1.1;\"\u003e40 L\u003c\/div\u003e\n\u003cdiv style=\"font-size: .85em; opacity: .95; margin-top: 4px;\"\u003eStorage capacity\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"background: #008377CF; color: #ffffff; padding: 18px 12px; border-radius: 8px; text-align: center;\"\u003e\n\u003cdiv style=\"font-size: 1.45em; font-weight: bold; line-height: 1.1;\"\u003e1¼\"\u003c\/div\u003e\n\u003cdiv style=\"font-size: .85em; opacity: .95; margin-top: 4px;\"\u003eInlet\/outlet connections\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"background: #008377CF; color: #ffffff; padding: 18px 12px; border-radius: 8px; text-align: center;\"\u003e\n\u003cdiv style=\"font-size: 1.45em; font-weight: bold; line-height: 1.1;\"\u003eA\u003c\/div\u003e\n\u003cdiv style=\"font-size: .85em; opacity: .95; margin-top: 4px;\"\u003eEnergy rating\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"background: #008377CF; color: #ffffff; padding: 18px 12px; border-radius: 8px; text-align: center;\"\u003e\n\u003cdiv style=\"font-size: 1.45em; font-weight: bold; line-height: 1.1;\"\u003e2 yr\u003c\/div\u003e\n\u003cdiv style=\"font-size: .85em; opacity: .95; margin-top: 4px;\"\u003eParts warranty\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"background: #e6f4f3; border-left: 4px solid #008377CF; padding: 14px 18px; margin: 0 0 22px; border-radius: 4px;\"\u003e\n\u003cstrong style=\"color: #005c54;\"\u003eSized to spec for the 11 and 13 kW Baxi heat pumps.\u003c\/strong\u003e Per the \u003cstrong\u003eBaxi HP40 \/ HP50 installation manual\u003c\/strong\u003e, the buffer tank requirement is \u003cstrong\u003e\u0026gt;25 L\u003c\/strong\u003e for 4–8 kW units and \u003cstrong\u003e\u0026gt;40 L\u003c\/strong\u003e for 11–13 kW units (and \u003cstrong\u003e\u0026gt;40 L per outdoor unit\u003c\/strong\u003e for cascade systems). The 40L is the right answer for the larger end of the range.\u003c\/div\u003e\n\u003ch3 style=\"background: #008377CF; color: #ffffff; padding: 12px 18px; margin: 28px 0 16px; border-radius: 6px; font-size: 1.15em; font-weight: 600; letter-spacing: .2px;\"\u003eKey features\u003c\/h3\u003e\n\u003cdiv style=\"display: grid; grid-template-columns: repeat(2,1fr); gap: 14px; margin: 0 0 24px;\"\u003e\n\u003cdiv style=\"background: #f0faf9; border: 1px solid #c8e6e3; border-radius: 8px; padding: 16px 18px;\"\u003e\n\u003ch4 style=\"margin: 0 0 8px; color: #005c54; font-size: 1.02em; font-weight: 600;\"\u003eSized for 11–13 kW heat pumps\u003c\/h4\u003e\n\u003cp style=\"margin: 0; font-size: .95em; line-height: 1.55;\"\u003eMeets Baxi's published \u003cstrong\u003e\u0026gt;40 L minimum buffer requirement\u003c\/strong\u003e for the 11 kW and 13 kW monobloc heat pumps — the simplest off-the-shelf solution for these units.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"background: #f0faf9; border: 1px solid #c8e6e3; border-radius: 8px; padding: 16px 18px;\"\u003e\n\u003ch4 style=\"margin: 0 0 8px; color: #005c54; font-size: 1.02em; font-weight: 600;\"\u003eReliable defrost performance\u003c\/h4\u003e\n\u003cp style=\"margin: 0; font-size: .95em; line-height: 1.55;\"\u003eStored thermal energy provides the volume the heat pump draws on during a defrost cycle, so radiators stay warm and the cycle completes cleanly.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"background: #f0faf9; border: 1px solid #c8e6e3; border-radius: 8px; padding: 16px 18px;\"\u003e\n\u003ch4 style=\"margin: 0 0 8px; color: #005c54; font-size: 1.02em; font-weight: 600;\"\u003eReduces short-cycling\u003c\/h4\u003e\n\u003cp style=\"margin: 0; font-size: .95em; line-height: 1.55;\"\u003eDampens the swing between flow and return temperatures, allowing the \u003cstrong\u003einverter compressor to modulate smoothly\u003c\/strong\u003e rather than starting and stopping — extending equipment life and reducing energy use.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"background: #f0faf9; border: 1px solid #c8e6e3; border-radius: 8px; padding: 16px 18px;\"\u003e\n\u003ch4 style=\"margin: 0 0 8px; color: #005c54; font-size: 1.02em; font-weight: 600;\"\u003eVolumiser or 4-port buffer\u003c\/h4\u003e\n\u003cp style=\"margin: 0; font-size: .95em; line-height: 1.55;\"\u003e\u003cstrong\u003eFlexible plumbing\u003c\/strong\u003e — install as a simple in-line volumiser (two ports) or as a fully decoupled 4-port buffer between primary and secondary circuits.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"background: #f0faf9; border: 1px solid #c8e6e3; border-radius: 8px; padding: 16px 18px;\"\u003e\n\u003ch4 style=\"margin: 0 0 8px; color: #005c54; font-size: 1.02em; font-weight: 600;\"\u003eGenerous 1¼\" connections\u003c\/h4\u003e\n\u003cp style=\"margin: 0; font-size: .95em; line-height: 1.55;\"\u003e\u003cstrong\u003e1 ¼\" inlet and outlet\u003c\/strong\u003e connection sizes match the typical pipework for larger ASHPs and keep pressure drop low across the buffer.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"background: #f0faf9; border: 1px solid #c8e6e3; border-radius: 8px; padding: 16px 18px;\"\u003e\n\u003ch4 style=\"margin: 0 0 8px; color: #005c54; font-size: 1.02em; font-weight: 600;\"\u003eA-rated insulation\u003c\/h4\u003e\n\u003cp style=\"margin: 0; font-size: .95em; line-height: 1.55;\"\u003e\u003cstrong\u003eA energy rating\u003c\/strong\u003e with thick foam insulation — minimal standby losses keep the stored heat where it is needed, in the system.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv style=\"background: #fff8e1; border-left: 4px solid #f59e0b; padding: 14px 18px; margin: 0 0 22px; border-radius: 4px;\"\u003e\n\u003cstrong style=\"color: #92400e;\"\u003eSizing rule from the Baxi installation manual.\u003c\/strong\u003e 4 \/ 5 \/ 7 \/ 8 kW heat pumps require \u003cstrong\u003e\u0026gt;25 L\u003c\/strong\u003e of buffer (the Baxi 24 L unit is sized to this). \u003cstrong\u003e11 and 13 kW heat pumps require \u0026gt;40 L\u003c\/strong\u003e — this is the unit you need. Cascade systems require \u003cstrong\u003e\u0026gt;40 L per outdoor unit\u003c\/strong\u003e.\u003c\/div\u003e\n\u003ch3 style=\"background: #008377CF; color: #ffffff; padding: 12px 18px; margin: 28px 0 16px; border-radius: 6px; font-size: 1.15em; font-weight: 600; letter-spacing: .2px;\"\u003eTechnical specifications\u003c\/h3\u003e\n\u003cdiv style=\"overflow-x: auto; margin: 0 0 24px;\"\u003e\n\u003ctable style=\"width: 100%; border-collapse: collapse; font-size: .95em;\"\u003e\n\u003ctbody\u003e\n\u003ctr style=\"background: #f0faf9;\"\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8; font-weight: 600; color: #005c54; width: 48%;\"\u003eManufacturer\u003c\/td\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8;\"\u003eBaxi\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background: #ffffff;\"\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8; font-weight: 600; color: #005c54; width: 48%;\"\u003eManufacturer part number (MPN)\u003c\/td\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8;\"\u003e7768655\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background: #f0faf9;\"\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8; font-weight: 600; color: #005c54; width: 48%;\"\u003eProduct family\u003c\/td\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8;\"\u003eBaxi air source heat pump accessories\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background: #ffffff;\"\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8; font-weight: 600; color: #005c54; width: 48%;\"\u003eCapacity\u003c\/td\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8;\"\u003e40 litres\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background: #f0faf9;\"\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8; font-weight: 600; color: #005c54; width: 48%;\"\u003eInlet \/ outlet connections\u003c\/td\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8;\"\u003e1¼\" BSP\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background: #ffffff;\"\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8; font-weight: 600; color: #005c54; width: 48%;\"\u003eEnergy rating\u003c\/td\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8;\"\u003eA\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background: #f0faf9;\"\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8; font-weight: 600; color: #005c54; width: 48%;\"\u003eMaximum working pressure\u003c\/td\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8;\"\u003e3 bar\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background: #ffffff;\"\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8; font-weight: 600; color: #005c54; width: 48%;\"\u003eMaximum operating temperature\u003c\/td\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8;\"\u003e95 °C\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background: #f0faf9;\"\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8; font-weight: 600; color: #005c54; width: 48%;\"\u003eMinimum operating temperature\u003c\/td\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8;\"\u003e6 °C\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background: #ffffff;\"\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8; font-weight: 600; color: #005c54; width: 48%;\"\u003eConfiguration\u003c\/td\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8;\"\u003eVolumiser or 4-port buffer vessel\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background: #f0faf9;\"\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8; font-weight: 600; color: #005c54; width: 48%;\"\u003eApplication\u003c\/td\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8;\"\u003eBaxi 11–13 kW monobloc ASHPs and cascade systems\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background: #ffffff;\"\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8; font-weight: 600; color: #005c54; width: 48%;\"\u003eWarranty\u003c\/td\u003e\n\u003ctd style=\"padding: 10px 14px; border-bottom: 1px solid #e8e8e8;\"\u003e2 years, parts only\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/div\u003e\n\u003ch3 style=\"background: #008377CF; color: #ffffff; padding: 12px 18px; margin: 28px 0 16px; border-radius: 6px; font-size: 1.15em; font-weight: 600; letter-spacing: .2px;\"\u003eFrequently asked questions\u003c\/h3\u003e\n\u003cdetails style=\"background: #f0faf9; border: 1px solid #c8e6e3; border-radius: 6px; margin: 0 0 8px; padding: 0;\"\u003e\n\u003csummary style=\"background: #008377CF; color: #ffffff; padding: 12px 16px; cursor: pointer; font-weight: 600; border-radius: 6px 6px 0 0; list-style: none;\"\u003eWhy do I need a buffer vessel with a heat pump?\u003c\/summary\u003e\n\u003cdiv style=\"padding: 14px 18px;\"\u003eA buffer adds \u003cstrong\u003esystem volume\u003c\/strong\u003e, which is essential for two reasons. First, it gives the heat pump the energy reserve it needs to run a clean defrost cycle in cold weather without dropping flow to the radiators. Second, it stops the compressor short-cycling on systems with low water content (e.g. mostly-TRV radiator circuits). Both effects directly improve seasonal efficiency.\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails style=\"background: #f0faf9; border: 1px solid #c8e6e3; border-radius: 6px; margin: 0 0 8px; padding: 0;\"\u003e\n\u003csummary style=\"background: #008377CF; color: #ffffff; padding: 12px 16px; cursor: pointer; font-weight: 600; border-radius: 6px 6px 0 0; list-style: none;\"\u003eWill the 40L work with my heat pump?\u003c\/summary\u003e\n\u003cdiv style=\"padding: 14px 18px;\"\u003eIt is sized specifically for the \u003cstrong\u003e11 kW and 13 kW Baxi monobloc heat pumps\u003c\/strong\u003e, where the installation manual mandates a buffer of more than 40 L. For smaller Baxi heat pumps (4–8 kW) the 24 L unit is sufficient. For other manufacturers, check the heat pump installation manual for the minimum-system-volume figure and pick a buffer that meets it.\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails style=\"background: #f0faf9; border: 1px solid #c8e6e3; border-radius: 6px; margin: 0 0 8px; padding: 0;\"\u003e\n\u003csummary style=\"background: #008377CF; color: #ffffff; padding: 12px 16px; cursor: pointer; font-weight: 600; border-radius: 6px 6px 0 0; list-style: none;\"\u003eCan I use it as a 2-port volumiser, or do I have to plumb it as a 4-port buffer?\u003c\/summary\u003e\n\u003cdiv style=\"padding: 14px 18px;\"\u003eBoth. The 40L can be plumbed as a simple \u003cstrong\u003ein-line volumiser\u003c\/strong\u003e (the heat pump circuit passes straight through it, adding volume) or as a fully decoupled \u003cstrong\u003e4-port buffer\u003c\/strong\u003e with separate primary and secondary pumps. Your installer will choose based on the system design — 4-port is more flexible for zoned systems with different flow demands.\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails style=\"background: #f0faf9; border: 1px solid #c8e6e3; border-radius: 6px; margin: 0 0 8px; padding: 0;\"\u003e\n\u003csummary style=\"background: #008377CF; color: #ffffff; padding: 12px 16px; cursor: pointer; font-weight: 600; border-radius: 6px 6px 0 0; list-style: none;\"\u003eWhat about insulation losses?\u003c\/summary\u003e\n\u003cdiv style=\"padding: 14px 18px;\"\u003eThe 40L is \u003cstrong\u003eA energy-rated\u003c\/strong\u003e with thick foam insulation, so standby losses are minimal. In a typical airing-cupboard or plant-room location the heat lost to the surroundings is offsetting space heating anyway.\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdetails style=\"background: #f0faf9; border: 1px solid #c8e6e3; border-radius: 6px; margin: 0 0 8px; padding: 0;\"\u003e\n\u003csummary style=\"background: #008377CF; color: #ffffff; padding: 12px 16px; cursor: pointer; font-weight: 600; border-radius: 6px 6px 0 0; list-style: none;\"\u003eDoes it come with a warranty?\u003c\/summary\u003e\n\u003cdiv style=\"padding: 14px 18px;\"\u003eYes — \u003cstrong\u003e2 years, parts only\u003c\/strong\u003e, as standard across the Baxi buffer vessel range. Register the parent heat pump on Baxi Works at the time of installation to keep all warranty paperwork in one place.\u003c\/div\u003e\n\u003c\/details\u003e\n\u003cdiv style=\"background: #008377CF; color: #ffffff; padding: 18px 22px; border-radius: 8px; margin: 30px 0 0; text-align: center;\"\u003e\n\u003cdiv style=\"font-size: 1.05em; font-weight: 600; margin-bottom: 6px;\"\u003eBuilding a complete heat pump system?\u003c\/div\u003e\n\u003cdiv style=\"font-size: .95em; opacity: .95;\"\u003ePair this buffer with a \u003cstrong\u003eBaxi HP40, HP50 or HP60 monobloc heat pump\u003c\/strong\u003e, the \u003cstrong\u003eBaxi ASHP Control\u003c\/strong\u003e, and a Baxi ASHP Cylinder for a complete MCS-compliant low-carbon heating package.\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e","brand":"Baxi","offers":[{"title":"Default Title","offer_id":64566916612445,"sku":"7768655","price":690.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0958\/2051\/3629\/files\/Baxi40LBufferVesselforAirSourceHeatPumps.webp?v=1777553436","url":"https:\/\/qualityheating.co.uk\/products\/baxi-40l-buffer-vessel-for-air-source-heat-pumps","provider":"AIZO Quality Heating","version":"1.0","type":"link"}