Does an ERV save more energy than it consumes?

Yes — a properly sized ERV typically recovers 3-5x more energy than its fan consumes. The fan uses 300-400 kWh/year, but the heat and moisture recovery prevents 1,000-2,000 kWh equivalent of HVAC conditioning energy, making the ERV a net energy saver.

ASHRAE 62.2 is the US ventilation standard requiring 0.03 CFM per sqft plus 7.5 CFM per occupant for acceptable indoor air quality. It is adopted by most US energy codes including IECC 2012+ and California Title 24. ERVs are the most common compliance solution for tight homes.

Solar ERV Calculator

Calculate required ventilation CFM per ASHRAE 62.2, ERV annual energy use, energy recovered vs consumed, and how many solar panels offset your ERV's electricity.

Home ventilation details

Home size?

sqft

Number of occupants?

people

Home airtightness?

Climate zone?

Current ventilation?

Your electricity rate?

$/kWh

Solar ERV system results

96 CFM required ventilation — 1 panel to offset ERV

Required ventilation (ASHRAE 62.2)96 CFM

Natural infiltration provided58 CFM

ERV sized to deliver96 CFM

ERV fan power77 W

ERV annual electricity use505 kWh/yr

Energy recovered by ERV (heating + cooling)4,526 kWh/yr equiv.

Net energy impact (recovered minus consumed)+4,022 kWh/yr (net saver)

Solar kW to offset ERV fan power0.38 kW (1 × 400W panel)

ERV installed cost$2,500

Solar cost (1-2 panels)$1,120

Total system cost (ERV + solar)$3,620

Annual net energy savings vs no ERV$169.78/yr

Payback period21.3 yrs

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How to Use This Calculator

Enter home size, occupants, and airtightness

ASHRAE 62.2 — the ventilation standard used by most US building codes — requires 0.03 CFM per square foot plus 7.5 CFM per occupant. Enter your conditioned floor area and number of permanent residents. Airtightness (ACH50) determines how much natural infiltration already provides: a leaky older home at 7 ACH50 may already get enough air changes; a tight 3 ACH50 home or Passive House at 0.6 ACH50 requires mechanical ventilation.

Select climate zone and current ventilation

Climate zone affects the energy recovery value: cold climates benefit heavily from heat recovery in winter; hot humid climates benefit from latent (moisture) recovery in summer. Current ventilation shows the baseline you're upgrading from — bathroom exhaust fans have zero energy recovery, while a prior HRV recovers heat but not moisture.

Read the results

The calculator shows required CFM, ERV fan power, annual electricity consumption, energy recovered (the ERV's benefit), and net energy impact. The key insight: a properly sized ERV typically recovers more energy than it consumes — making it a net energy saver, not just a ventilation cost. Solar panels needed to offset the ERV is often just 1-2 panels.

The Formula

Required CFM (ASHRAE 62.2) = 0.03 × sqft + 7.5 × occupants Natural Infiltration CFM = (ACH50 ÷ 17) × Volume ÷ 60 ERV Fan Power ≈ 0.8 W per CFM (at design flow) ERV Annual kWh = Fan Watts × 18 hrs/day × 365 ÷ 1000 Recovery (kWh) = CFM × 60 × Heating Days × ΔT × 1.1 Btu × 0.75 efficiency ÷ 3412 Net Energy Impact = Energy Recovered − ERV kWh consumed Solar kW = ERV Daily kWh ÷ Peak Sun Hours (4.5) ÷ 0.80

The ERV efficiency of 75% represents combined sensible and latent recovery — typical of quality residential ERV units. The ERV runs approximately 18 hours per day on intermittent cycling schedules, not continuously. Recovery is calculated separately for heating and cooling seasons based on your climate zone's heating and cooling days.

Example

The Petersons — Tight new construction, 4 people, mixed climate

The Petersons are building a new 2,200 sqft home in zone 5 (Minneapolis adjacent). The builder achieved 3 ACH50 on the blower door test — code-compliant but tight enough that ASHRAE 62.2 says they need mechanical ventilation. They want to add an ERV and offset it with solar.

Home size2,200 sqft

Occupants4 people

Airtightness3 ACH50 (tight)

ClimateMixed (Zone 5)

Rate$0.13/kWh

Result

Required CFM96 CFM

ERV annual electricity~315 kWh/yr

Energy recovered~1,100 kWh/yr equiv.

Net energy impact+785 kWh/yr (net saver)

Solar to offset ERV1 × 400W panel

Total system cost~$3,620

Annual energy savings~$41/yr

One solar panel completely offsets the ERV's fan electricity. Meanwhile the ERV recovers 1,100 kWh equivalent of heating and cooling energy per year — 3.5x more than it consumes. The Petersons get ASHRAE 62.2 compliant fresh air, reduced HVAC load, and controlled moisture — with one panel making the whole system net-zero electrically.

FAQ

What is the difference between an ERV and an HRV? ▼

Both recover heat from exhaust air before it leaves the house. An HRV (Heat Recovery Ventilator) recovers only sensible heat — temperature. An ERV (Energy Recovery Ventilator) recovers both sensible heat and latent energy (moisture). In cold dry climates, HRVs are preferred because they remove excess indoor humidity. In hot humid climates, ERVs are better because they prevent humid outdoor air from entering. In mixed climates, ERVs are generally preferred for year-round performance. Both use 50-100W of fan power and recover 70-85% of the energy in exhaust air.

Why does an ERV use less energy than it saves? ▼

An ERV's fan uses 50-100W to move air — typically 300-400 kWh per year. But the heat and moisture it recovers represents far more energy: preventing your furnace or AC from conditioning that incoming fresh air. In a cold climate home, bringing in 96 CFM of 15°F outdoor air and heating it to 70°F takes about 1,400 kWh equivalent of heat energy per winter. The ERV recovers 75% of that — about 1,050 kWh — using only 300 kWh of fan power. Net result: 750 kWh saved annually. This is why building scientists call ERVs "energy-positive" ventilation.

Do I need an ERV if my home is leaky (older construction)? ▼

Probably not for IAQ — a leaky home at 7 ACH50 gets plenty of air exchange through natural infiltration. In fact, it gets too much: uncontrolled infiltration means drafts in winter, humidity swings, and pollen/pollution entry. However, if you're air-sealing an older home as part of an energy retrofit, you should add an ERV once you get below 5 ACH50. ASHRAE 62.2 requires mechanical ventilation for homes below a certain infiltration threshold. The ERV pays for itself in energy saved from conditioning that uncontrolled air infiltration.

How many solar panels does an ERV need? ▼

Very few — typically 1 to 2 panels (400W each). A typical residential ERV uses 300-400 kWh per year. At 4.5 peak sun hours and 80% system efficiency, one 400W panel produces about 525 kWh per year — enough to fully offset most ERVs. This makes solar-powered ERV ventilation an extremely affordable upgrade. The ERV itself costs $2,000-3,500 installed; adding one solar panel adds $1,200-1,500 to the project. The combined system is one of the best dollar-per-IAQ-improvement investments available.

What is ASHRAE 62.2 and does my home need to comply? ▼

ASHRAE 62.2 is the ventilation standard for low-rise residential buildings, adopted by most US energy codes including IECC 2012+ and California Title 24. It requires minimum ventilation rates of 0.03 CFM/sqft + 7.5 CFM/person for acceptable indoor air quality — protecting against CO2 buildup, VOCs, radon, and moisture. If you're building new or doing an energy retrofit that includes air sealing, your jurisdiction likely requires compliance. Existing homes are not retroactively required to comply, but tight existing homes without mechanical ventilation have measurably worse IAQ. ERVs are the most common compliance solution.

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