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Will a heat pump work in an old house?

It can, but only where the fabric has been upgraded enough for the house to be heated at low flow temperatures. Without insulation and airtightness work, a heat pump will run at high flow temperatures, giving poor efficiency and high bills.

Heat pumps deliver their efficiency by producing large volumes of moderately warm water rather than small volumes of very hot water. That means emitters must be sized for a lower flow temperature, often meaning larger radiators or underfloor heating.

SEAI's heat pump grant requires a technical assessment demonstrating the heat loss indicator is within range, which is a useful discipline even if you are not claiming the grant.

Work usually needed first

  • Attic insulation upgraded to current levels
  • Wall insulation, cavity fill or internal or external systems
  • Draught-proofing and airtightness improvement
  • Emitter resizing and pipework capacity check
  • Hot water cylinder suitable for heat pump operation

Sources

Last reviewed 28 August 2026. General information only — not legal or planning advice.

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