Size liquid and suction lines and calculate the additional refrigerant charge for a split or multi split installation. Enter the unit, pipe run and refrigerant and the calculator returns recommended line sizes, the trim charge beyond the pre-charged length, A2L flammability flags where relevant and the F-Gas CO2 equivalent of the total charge.

Getting pipe runs right

Refrigerant pipework is one of the least forgiving parts of an air conditioning installation. Undersized suction lines rob capacity and strain the compressor; oversized lines can fail to return oil at part load; and an incorrect additional charge, in either direction, degrades performance and can shorten equipment life. Manufacturers publish limits for a reason, and this calculator keeps your installation inside them.

What the calculator works out

Line sizes. Recommended liquid and gas line diameters for the capacity, refrigerant and run length entered, with sanity check flags when a run is long enough or a lift large enough that the manufacturer's specific tables should be consulted before ordering.

Additional refrigerant charge. Almost all splits come pre-charged for a standard pipe length, commonly 7.5 m. Beyond that, refrigerant must be added per metre of liquid line, at a rate that depends on the liquid line diameter and refrigerant. The calculator works out the trim charge for your actual run so the system is neither starved nor overcharged.

A2L safety flags. R32 and R454B are class A2L mildly flammable refrigerants. The calculator flags A2L refrigerants and reminds you of the implications: charge limits relative to room size, appropriate tooling and ventilation practice during installation. Where a charge and room combination looks tight against minimum room size considerations under EN 378 and IEC 60335-2-40, the tool says so rather than staying quiet.

F-Gas CO2 equivalent. The total system charge expressed in tonnes of CO2 equivalent, which determines leak checking obligations under the F-Gas Regulation and is increasingly requested on handover documentation. R32's GWP of 675 against R410A's 2088 is one reason the industry has moved: the calculator makes the difference visible for your actual charge.

Methods and standards

Line sizing follows conventional velocity and pressure drop practice for halocarbon refrigerants consistent with manufacturer guidance and ASHRAE refrigeration practice. Charge calculations use published per-metre trim rates by liquid line size and refrigerant. Flammability classification and room size considerations reference EN 378 and IEC 60335-2-40. GWP figures follow the F-Gas Regulation reporting basis.

Results are indicative. Manufacturer installation manuals take precedence for every specific unit: maximum pipe lengths, height differences, charge rates and oil return requirements vary by model. Refrigerant handling and charging must only be carried out by F-Gas certified engineers.

Who this tool is for

F-Gas engineers and installers confirming line sizes and trim charge before ordering pipe and refrigerant. Contractors checking whether a proposed outdoor unit position keeps runs within limits before the quote goes out. Surveyors and estimators pricing pipe runs and charge accurately instead of guessing.

Frequently asked questions

How much refrigerant do I add per metre of pipe? It depends on the liquid line diameter and refrigerant. As a typical example, R32 systems with a 6.35 mm liquid line commonly require around 20 g per metre beyond the pre-charged length, but rates vary by manufacturer and line size. Enter your system above for a calculated trim charge, and always confirm against the installation manual.

What pipe size do I need for a 5 kW air conditioning unit? Most 5 kW class R32 splits use a 6.35 mm (1/4 inch) liquid line and a 12.7 mm (1/2 inch) gas line, but this varies by manufacturer and model. The calculator recommends sizes from capacity and refrigerant, and flags when the run length means the manufacturer's tables must be checked.

Is R32 refrigerant dangerous? R32 is classified A2L: low toxicity and mildly flammable. It is safe when installed correctly, but it carries requirements that R410A did not: minimum room sizes for a given charge, A2L rated tools and no brazing on a charged system. The calculator flags A2L refrigerants and highlights when room size deserves a closer check.

What is the F-Gas CO2 equivalent and why does it matter? It is the refrigerant charge in kilograms multiplied by the refrigerant's global warming potential, expressed in tonnes of CO2 equivalent. It determines statutory leak check frequency: systems of 5 tonnes CO2e or more require periodic leak checking. The calculator reports the figure for your total charge.

Can I install air conditioning refrigerant pipework myself? Pipework installation practices vary, but any work involving refrigerant, including charging, recovery and breaking into circuits, legally requires F-Gas certification in the UK. Use this calculator to plan and price the installation, and have a certified engineer carry out the refrigerant work.

Related tools

• [Cooling and Heating Load Estimator]: size the unit before sizing its pipework
• [Duct Sizing Calculator]: for ducted air conditioning systems