Heat Recovery Ventilator Energy Savings Calculator

Introduction to HRV energy savings

A heat recovery ventilator energy-savings estimate is most useful when you want to know how much heating demand is tied to the ventilation air you intentionally bring into a building. An HRV lets outdoor air in and stale indoor air out at the same time, but the two streams pass on opposite sides of a heat exchanger so part of the outgoing heat is handed back to the incoming air.

This calculator turns that idea into three daily figures: the ventilation heat loss you would expect without recovery, the amount of heat an HRV can reclaim at the efficiency you choose, and the dollar value of that recovered heat at your heating price. It is not a building-model substitute, but it is a practical way to compare operating scenarios, equipment ratings, and weather conditions.

If you are trying to judge whether an HRV will matter in your home or project, the central question is simple: how much heat does your ventilation airflow carry away, and how much of that energy can the exchanger give back before the furnace, boiler, or heat pump has to replace it?

How to use this HRV calculator

To estimate HRV savings, start with the size of the conditioned space, then describe how hard the ventilation system works, how cold the outdoor air is, how efficient the core is, and what you pay for heat. The form uses metric units and produces results in kWh per day and dollars per day. If you are comparing design options, it usually helps to keep the building volume and energy price fixed while you vary ACH, temperature difference, and efficiency across a few runs.

1. Enter building volume in m³. A quick estimate is floor area multiplied by average ceiling height.
2. Enter air changes per hour (ACH). This should represent intentional ventilation airflow, not necessarily uncontrolled leakage.
3. Enter the indoor to outdoor temperature difference in °C for the period you want to examine.
4. Enter HRV efficiency as a percent. Use sensible heat recovery efficiency if that is what the product literature reports.
5. Enter heating cost in $ per kWh of delivered heat, then press Calculate.

After calculation, the result area reports the daily ventilation heat loss without recovery, the daily energy the HRV recovers, and the estimated daily cost savings. The summary table repeats those numbers in a compact format that is easy to scan or share.

Formula and assumptions for HRV energy savings

The HRV energy-savings formula starts with the sensible heat needed to warm incoming ventilation air from the outdoor temperature to the indoor temperature. To keep the estimate transparent, the calculator uses dry-air approximations: air density ρ ≈ 1.2 kg/m³ and specific heat c_p ≈ 1000 J/(kg·K). Those values are good enough for a quick comparison even though real air properties shift slightly with humidity and temperature.

First, the calculator finds the steady ventilation heat loss rate in watts.

Formula: Q = ρ × c_p × V × ACH × ΔT /3600

That heat loss rate is then converted to daily energy in kWh per day. Recovered energy is the chosen efficiency fraction of that loss.

Formula: E_saved = η × E_loss

Finally, the daily cost savings are the recovered kWh multiplied by your heating cost per delivered kWh. Because the result scales directly with airflow, ΔT, and efficiency, cold weather, high ventilation rates, and a strong heat exchanger all push the savings upward.

Worked example: a 250 m³ home at 0.5 ACH

For a straightforward HRV example, imagine a home with a volume of 250 m³ that is ventilated at 0.5 ACH. If the indoor temperature is 20 °C and the outdoor temperature is 0 °C, then the temperature difference is 20 °C. Using the calculator's assumptions gives a useful back-of-the-envelope estimate.

• Heat loss rate: Q ≈ (1.2 × 1000 × 250 × 0.5 × 20) / 3600 ≈ 833 W
• Daily loss: E_loss ≈ 833 × 24 / 1000 ≈ 20.0 kWh/day
• If HRV efficiency is 70 percent, E_saved ≈ 0.70 × 20.0 ≈ 14.0 kWh/day
• If heating cost is $0.15 per kWh, savings ≈ 14.0 × 0.15 ≈ $2.10 per day

The result is small enough to feel realistic on a daily basis but large enough to matter across an entire heating season. Over 150 heating days, that simple example suggests roughly $315 of recovered heating value. Actual savings still depend on weather, operating schedule, and equipment performance, but the example makes the relationships easy to see: doubling ACH roughly doubles the loss, a colder day increases the loss in direct proportion to ΔT, and a better exchanger captures a larger share of that total.

Typical HRV efficiency ranges

HRV performance depends on airflow balance, duct layout, core design, test conditions, and frost strategy. The table below gives representative sensible heat recovery efficiencies so you can choose a starting point when exact product data is unavailable.

Limitations and practical notes for HRV savings

This HRV energy-savings calculator is intentionally simplified so you can see the main drivers without wading through a full building model. That makes it ideal for comparison and early planning, but it also means you should read the output as an estimate rather than a guaranteed bill reduction. Several practical effects are deliberately left outside the model.

• Constant conditions: it assumes the same ACH and the same temperature difference all day.
• Sensible heat only: it does not model moisture transfer or latent energy in detail.
• No fan power subtraction: the electrical energy used by HRV or ERV fans is not deducted from the recovered heat value shown.
• No detailed duct effects: duct losses, defrost cycles, leakage, and balancing issues can change real-world performance.
• Heating system efficiency matters: your effective cost per delivered kWh of heat may differ from your utility rate if you use gas, oil, pellets, or a heat pump.

Even with those simplifications, the calculator remains useful because it highlights the dominant drivers. If the savings are small even under favorable inputs, a premium HRV may not be justified purely on heat recovery. If the savings are substantial, the tool gives you a quick screening result before you move on to a more detailed design analysis.

Additional HRV context: interpreting results

Good ventilation matters for health and comfort. Fresh air dilutes carbon dioxide, odors, volatile organic compounds, and excess moisture. In newer airtight homes, that usually means relying on mechanical ventilation instead of accidental leakage. The downside is simple: if you bring in cold air without recovery, the heating system has to do extra work every hour that ventilation runs.

HRVs reduce that penalty by tempering incoming air. The result is often better comfort near diffusers, lower peak heating demand associated with ventilation, and a more predictable indoor environment. Installation quality matters just as much as brochure efficiency, though. Short insulated duct runs, balanced airflow, clean filters, and proper commissioning help the unit operate close to its rated performance.

When you read the calculator output, remember that it expresses the thermal value of recovered heat. If you heat with a resistance heater, the price per delivered kWh of heat may be close to your electric rate. If you heat with a heat pump, your effective delivered heat cost is lower because each purchased kWh of electricity can deliver multiple kWh of heat. If you heat with combustion equipment, the delivered heat cost depends on the fuel price and the appliance efficiency.

You can still use the tool for non-electric fuels. Convert your fuel cost into a cost per delivered kWh of heat, then enter that value in the heating cost field. Doing so makes the daily savings number more meaningful, especially when you are comparing equipment upgrades or trying to estimate a seasonal payback.

Another useful way to interpret the output is as a sensitivity test. Run one case at 0.3 ACH, another at 0.5 ACH, and another at 0.7 ACH. Then do the same with low and high temperature differences. That exercise often reveals whether the project is mainly sensitive to climate, ventilation design, or exchanger efficiency. It also helps communicate the value of balanced ventilation to clients, homeowners, or project teams who may not think in heat-flow terms every day.

FAQ about HRV savings

Is ACH the same as infiltration?

Not in this HRV calculator. ACH is the intentional ventilation rate from fans and ducts, while infiltration is uncontrolled leakage through the building envelope. Real buildings experience both. If you want a conservative rough estimate of total air exchange heat loss, you can test a somewhat higher ACH to reflect the combined effect.

What temperature difference should I use?

Use a representative average ΔT for the period you care about, because the HRV savings estimate scales directly with that gap. For a typical cold day, indoor 20 °C and outdoor 0 °C gives ΔT = 20 °C. For a longer planning view, use a seasonal average outdoor temperature or run several scenarios such as 10, 20, and 30 °C to see how strongly the result moves.

Does HRV efficiency stay constant?

No. Published efficiency is measured under specific airflow and temperature conditions. Real performance can drop because of frost control, dirty filters, unbalanced airflow, or poor duct insulation. If you want a cautious estimate, enter a lower value than the headline rating.

Why are the results shown per day?

Daily numbers are easy to understand and easy to scale. Multiply the outputs by the number of heating days you want to examine to estimate a seasonal total. Many users test several season lengths, such as 120, 150, and 180 days, to see the range of likely outcomes.

Can I use this for an ERV?

Yes for a rough sensible-heat estimate. ERVs can also transfer moisture, which can matter in humid climates or shoulder seasons, but that latent component is not modeled here. Treat the result as the sensible portion of the savings.

What about fan electricity?

Fan energy is not subtracted in this calculator. If you know the unit's average fan power, estimate its daily kWh use and subtract that from the recovered energy for a rough net value. That step is optional for comparison work, but it improves realism when you are estimating actual operating cost impact.

Accessibility note: after you press Calculate, the results region updates inside a live status area. The Copy Summary button becomes available only after a successful calculation.