Old copper can be reused only when it is the right diameter for the new equipment, it is clean inside, and it has been pressure tested. That decision belongs to the F-gas engineer against the new manufacturer's instructions. R410A to R32 is not a gas swap. A different refrigerant is not poured into the old pipes and the old outdoor unit and called a conversion. If the diameter, the condition or the manual is wrong, the new system gets new pipe.
Diameter, a clean bore, and a test on the day
Diameter has to match the new indoor and outdoor pair. A line that suited the old unit can be too small or too large for the new one. Any one of those conditions failing is enough to fit new copper.
Old oil, a pressure test, and a gas that is not a swap
Clean means free of the old oil contamination, moisture and debris the new manual will not accept. Pressure tested means the engineer has proved the reused run holds, as a customer-visible step on install day, not a hope that it held ten years ago.
R410A and R32 are different refrigerants with different system designs. Replacing an old pair with a new R32 pair is a new installation: recovery of the old charge, then a new matched system. Leaving the old outdoor unit in place and changing the gas is not that job. Flushing, if the engineer and the manual allow the old pipe at all, is part of their work. It is not a DIY flush. This page does not describe how to do it.
A manufacturer who expects new pipe may exclude a failure on reused line. Ask the price to say reused or new, the diameters, and that a pressure test is included. Energy Saving Trust's air-to-air heat pump guidance assumes a proper install. It does not authorise old pipe.
The new condenser still has a siting check
The outdoor position of the new unit still has to meet Planning Portal rules in England, whether the copper is old or new. The F-gas engineer decides, using the new manufacturer's instructions.
Frequently asked questions
Can I reuse the pipes if they look fine outside?
Only if the diameter is right, the inside is clean enough for the new manual, and the engineer pressure tests them. The outside look is not the test.
Is moving from R410A to R32 just a different gas in the same pipes?
No. R410A to R32 is not a gas swap. It is a new matched system. Old pipe is a maybe, and only on the three conditions: right diameter, clean inside, and pressure tested.
Who decides if the old copper stays?
The F-gas engineer, using the new manufacturer's instructions. If they cannot meet those conditions, they should price new pipe.
Does buried pipe I cannot see still count as reusable?
Buried pipe you cannot inspect is the usual reason to refuse reuse. If the diameter, the condition or the manual is wrong, the new system gets new pipe.
Core buying guides
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Related guides
Sources and further reading
How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.