Minimum inverter size required for a hot water heater?

Sizing Inverters for Hot Water Heaters

When sizing an inverter for a hot water heater, it’s essential to consider the device’s power consumption and the inverter’s efficiency. A typical 50-gallon storage tank requires approximately 4,000-6,000 watts of power to heat the water from 50°F to 120°F. However, most electric hot water heaters have an element that only operates intermittently, with a 30-40% duty cycle. This means the inverter doesn’t need to supply the full power rating all the time.

Inverter Sizing Calculation

To calculate the minimum inverter size required, consider the hot water heater’s power consumption and duty cycle. A common rule of thumb is to oversize the inverter by 20-30% to account for the inverter’s own efficiency losses and any future upgrades. Using the example above, a 50-gallon storage tank would require a 4,000-6,000 watt inverter. To oversize the inverter by 20-30%, we would need a 4.8-7.2 kW or 5-7.2 kW inverter, respectively.

Inverter Selection Considerations

When selecting an inverter for a hot water heater, it’s crucial to consider the device’s efficiency, voltage rating, and temperature range. Look for an inverter with a high efficiency rating (e.g., 95% or higher) to minimize energy losses. Additionally, ensure the inverter is rated for the hot water heater’s voltage and temperature range. A 240-volt inverter is typically required for a standard 240-volt hot water heater, and the inverter should be capable of operating in temperatures ranging from -20°C to 40°C (-4°F to 104°F).