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Comparison guide

Air source heat pump vs air-to-air

The confusing part is usually not the technology name. It is that the survey, design, and compliance questions change depending on whether the job is a wet system or an air-to-air route.

Air source survey overview Air-to-air guide
At a glance

The practical difference is what the system feeds

Wet ASHP
  • Feeds radiators, underfloor, or other wet emitters
  • Hot-water and cylinder questions often matter
  • Emitter suitability and heat-loss inputs sit closer to the centre of the job
Air-to-air
  • Feeds indoor air units rather than wet emitters
  • Line routes, indoor unit placement, and condensate handling move up the list
  • Cooling and zoning conversations may also matter earlier
Shared
  • External unit siting still matters
  • Electrical context still matters
  • Bad early assumptions still create quote churn and install friction
What changes on site

The survey route should match the first unresolved questions

Choose wet ASHP first when

The job depends on emitter upgrades, heat-loss inputs, cylinder layout, hot-water strategy, or the office team needs a wet-system handoff for design and install.

Choose air-to-air first when

The real decisions are indoor unit layout, room coverage, refrigerant line routes, condensate handling, and whether the building is better served by an air-delivery route than a wet retrofit.

Do not mix them up when

The brochure language sounds similar but the site questions are different. That is where teams lose time and end up surveying the wrong problem first.

ASHP survey packs Air-to-air heat pumps guide Heat loss calculations