How to Estimate Heat Recovery Savings and Payback
Heat recovery projects live or die by the payback number. The calculation itself is straightforward: estimate how much energy you recover per year, multiply by your energy cost, and divide by the installed cost of the exchanger. Below is a practical way to build that estimate for air-to-air applications.
Step 1: Gather the airflow and temperature data
You need the supply airflow (m³/h) and the temperature difference between the exhaust air leaving the process and the outdoor air entering it. Use the design winter or peak operating condition for conservative sizing, and the average condition for annual savings.
Step 2: Calculate recoverable power
For air, a useful rule of thumb is:
Recovered power (kW) ≈ Airflow (m³/h) × ΔT (K) × 0.00034
The constant 0.00034 accounts for air density and specific heat at typical operating conditions. For example, 5,000 m³/h with a 40 °C temperature difference gives roughly 68 kW of recoverable power.
Step 3: Apply the exchanger efficiency
No real exchanger recovers 100% of the available energy. Multiply the recovered power by the expected efficiency:
- Counter-flow plate: 60–75% sensible
- Cross-flow plate: 50–65% sensible
- Rotary enthalpy wheel: 70–85% total (sensible + latent)
- Heat pipe: 50–70% sensible
Continuing the example, a 70% efficient counter-flow plate on a 68 kW stream delivers about 48 kW of usable heat.
Step 4: Annual savings and payback
Multiply the net recovered kW by annual operating hours and your energy cost per kWh. For continuous processes running 6,000 h/yr at €0.12/kWh, 48 kW recovers about €34,560 per year. Against an installed heat recovery unit cost of €50,000–70,000, the simple payback is roughly 1.5–2 years.
Use the calculator
For a first-order estimate without building a spreadsheet, use our free Heat Recovery Savings Calculator. It handles the sensible-heat arithmetic and payback estimate in one screen. If your project is a drying line, the Drying Heat Recovery Calculator includes exhaust moisture and runtime assumptions specific to ovens and dehumidifiers.
What the calculator does not include
The basic estimate is gross recovered energy. For net savings, subtract the extra fan power needed to overcome the exchanger pressure drop — typically 5–15% of the recovered energy. Also include any preheating, bypass dampers or frost protection required in your climate.