- Enter airflow and sensible effectiveness from your unit specs.
- Estimate seasonal hours and average temperature differences.
- Set energy prices, heating efficiency, and cooling COP.
- Add fan power and maintenance to capture operating costs.
- Provide installed cost and rebates, then choose analysis years.
- Review net savings, payback, ROI, and NPV. Export if needed.
The calculator estimates recovered sensible energy using a common airflow heat-transfer approximation:
- BTU/hr ≈ 1.08 × CFM × ΔT(°F)
- Annual recovered BTU = BTU/hr × hours × effectiveness
- Thermal kWh = BTU / 3412
- Heating savings = (thermal kWh / heating efficiency) × heating price
- Cooling savings = (thermal kWh / COP) × electricity price
- Net savings = heating + cooling − fan cost − maintenance
- NPV = Σ cashflow(year) / (1 + discount rate)^year
This is a planning model. Real savings depend on climate, duct losses, control settings, infiltration, and how often bypass/defrost modes run.
| Example inputs | Value | What it represents |
|---|---|---|
| Airflow | 120 CFM | Average balanced ventilation rate |
| Effectiveness | 70% | Sensible heat recovery effectiveness |
| Heating hours / ΔT | 1800 h / 35°F | Heating season operating conditions |
| Cooling hours / ΔT | 800 h / 15°F | Cooling season operating conditions |
| Energy prices | $0.12 / $0.18 | Heating kWh equivalent / electricity |
| Installed cost / rebate | $1700 / $250 | Upfront investment and incentives |
Energy recovery and annual loads
Heat recovery ventilation reduces the sensible load created by continuous fresh air. The model uses 1.08 × CFM × ΔT to estimate hourly BTU transfer, then multiplies by seasonal hours and sensible effectiveness. Example: 120 CFM, 35°F heating delta, 1,800 heating hours, and 70% effectiveness recovers about 5.3 million BTU, roughly 1,560 thermal kWh per year. Cooling recovery uses your cooling hours and delta.
Turning recovered energy into savings
Recovered thermal energy becomes savings after equipment performance is applied. Heating savings divide recovered thermal kWh by heating efficiency, then multiply by your heating price per kWh equivalent. Cooling savings convert thermal kWh to electric kWh using COP; a COP of 3.2 means 3.2 thermal kWh avoided saves 1 electric kWh. Fan electricity and annual maintenance are subtracted to produce net savings.
Payback, ROI, and NPV outputs
Net upfront cost equals installed cost minus rebates. Simple payback is net cost divided by net annual savings. ROI compares total net savings over the analysis period with the upfront cost, and can include a replacement event. NPV discounts each year’s cash flow by (1 + discount rate)year, which emphasizes earlier savings and reflects the value of money over time.
Sensitivity drivers and realistic ranges
Airflow, seasonal hours, and temperature difference drive results. Doubling airflow roughly doubles recovered energy. Mild climates with 800 heating hours and a 20°F delta may show modest savings, while colder conditions with 2,500 hours and a 40°F delta can improve payback. Fan power also matters: higher wattage raises operating cost, especially when electricity rates are high.
Using results for practical decisions
Compare scenarios by adjusting effectiveness, energy prices, and incentives. If payback is borderline, stress test by lowering seasonal deltas and hours by 15–25%. Export the report for budgeting and to track assumptions. The chart visualizes annual cash flow so you can see whether savings remain steady across years as prices escalate for decision clarity.
It is the percentage of temperature difference the unit can transfer between outgoing and incoming air streams under steady conditions. Higher values usually increase savings, but real performance can vary with airflow, frost control, and installation.
Use local weather patterns and your thermostat setpoint. Approximate the number of hours where indoor–outdoor differences are meaningful, then use an average temperature difference during those hours. Conservative estimates help prevent overstating savings.
The HRV needs power to move air. That electricity is a real operating cost and can offset part of the heating and cooling savings, especially with high airflow, long runtime, or higher electricity rates.
Enter an effective “heating efficiency” that reflects typical seasonal performance, or convert heating to an equivalent electric cost. For more precision, treat heating price as electricity price and use an efficiency that represents your average seasonal COP.
Payback shows how quickly savings recover the upfront cost. NPV discounts future cash flows using your discount rate, helping compare this upgrade with other investments where time and risk matter.
Use measured airflow, confirm effectiveness at your intended speed, and refine hours and temperature differences with local climate data. Include maintenance, realistic rebates, and any mid‑life replacement costs so the financial metrics match your project plan.