Two technologies dominate any conversation about lowering HVAC energy cost — air-to-air heat recovery (ERV/HRV) and the heat pump. They are often confused because both "move heat", but they solve different halves of the problem. Pick the wrong one and you leave 30–60% of the saving on the table. This guide is the decision shortcut; the full economics are in our Economics Guide (Pillar).
What each one actually does
A heat-recovery unit transfers energy that is already in the building's exhaust air back into the incoming supply air — no compressor, no refrigerant, near-zero running cost. An air-source heat pump uses a compressor and refrigerant cycle to pull heat from outdoors (or reject it) and deliver 3–5× the energy it consumes as useful heating or cooling. One recycles; the other upgrades.
Use heat recovery when you are throwing air away
If a space needs ventilation (offices, schools, kitchens, laboratories, data centres), you are exhausting conditioned air continuously. That is free energy leaving the building. An ERV/HRV grabs 60–85% of it on the way out. The rule of thumb: if outdoor-air fraction exceeds ~30% of total supply, heat recovery pays for itself fast — model it with the savings tool and the payback tool. See applications across our Applications Guide (Pillar).
Use a heat pump when you lack a heat source inside
A heat pump is the right answer when the job is heating or cooling a space and there is no exhaust stream to mine — homes, warehouses, process water. It does not need ventilation to work; it pulls low-grade heat from the ambient and upgrades it. Where both a ventilation load and a heating load exist, the two are complementary, not competing — see heat pump + ERV combinations.
Heat recovery vs heat pump: decision table
| Condition | Best fit | Why |
|---|---|---|
| High ventilation rate, conditioned exhaust | ERV / HRV | Free recycling, no compressor energy |
| Heating/cooling, little or no exhaust | Heat pump | Upgrades ambient heat efficiently |
| Hot-humid climate, ventilation load | Enthalpy ERV | Recovers both heat and moisture |
| Both ventilation + heating load | Heat pump + ERV | Each covers its half; see combination design |
| Retrofit, tight budget | Heat recovery first | Lowest cost per kWh saved; retrofit ROI |
Worked example
A 5,000 m² office exhausts 20,000 m³/h of 22°C air, 2,500 h/yr, winter −5°C. Heat recovery at 80% effectiveness recovers roughly 110 MWh/yr — about €11k at €0.10/kWh, ~1.5-year payback. Adding a heat pump for perimeter heating would be a separate ~40 MWh/yr load. Combined, the ERV shrinks the heat-pump duty first, so the pump runs smaller and cheaper. Both tools confirm the numbers.
The one-line rule
Mining your own exhaust? → heat recovery. No exhaust to mine? → heat pump. Have both loads? → run heat recovery first, then size the heat pump on the remainder.
Not sure which your building needs?
Send us the ventilation rate, climate and loads — we will size heat recovery, heat pump, or both.
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