How pool heating costs are compared

Gas Heating Economics

Modern gas pool heaters typically convert about 80 to 85% of the gas energy into heat for the pool water. The energy content of natural gas is approximately 38.7 MJ/m³, and Victorian gas tariffs are structured with fixed supply charges plus volumetric consumption rates. Our model calculates the total MJ required to maintain target temperature across all seasons, applies the heater's thermal efficiency, converts to cubic metres of gas consumed, and applies current tariff structures including GST and supply charges.

Heat Pump Performance Curves

A heat pump takes heat from the air. In good conditions, it may deliver about 4 to 6 kWh of heat for each 1 kWh of electricity used. However, COP degrades significantly at low ambient temperatures. Our model uses manufacturer-specific performance curves that map COP against ambient temperature and humidity. For Melbourne's climate, this means: • Summer (25°C+): COP 5.0 to 6.2 • Autumn/Spring (15°C): COP 3.5 to 4.5 • Winter (5 to 10°C): COP 2.0 to 3.0 • Below 5°C: Defrost cycles further reduce effective COP The annual weighted-average COP for Melbourne typically falls between 3.5 to 4.5, depending on the specific unit and heating season length.

• COP curves interpolated from manufacturer test data at multiple ambient conditions
• Defrost cycle energy penalty modelled below 7°C ambient
• Humidity correction factor for air-source heat extraction efficiency
• Compressor cycling losses at part-load conditions

Solar Thermal Analysis

Solar pool heating uses unglazed polymer collectors to absorb solar radiation and transfer heat to circulating pool water. System performance depends on collector area, orientation, tilt angle, and Melbourne's solar irradiance profile. Our model uses Bureau of Meteorology solar radiation data to calculate monthly energy harvest, accounting for: • Collector efficiency curve (typically 70 to 85% at low ΔT) • Incidence angle modifier for non-perpendicular solar radiation • Auxiliary pump energy consumption for collector circulation • Seasonal availability: solar heating works best from October to March and gives much less help from June to August in Melbourne.

Comparing the true cost per unit of heat

To compare heaters fairly, the tool estimates the cost of each megajoule of useful heat after allowing for purchase, installation, servicing and energy use. LCOH = (Capital + Installation + Maintenance + Energy) ÷ Total MJ Delivered This metric accounts for equipment replacement cycles (gas heaters: 8 to 12 years, heat pumps: 12 to 18 years, solar: 15 to 25 years) and maintenance costs, providing a true apples-to-apples comparison.

Carbon Emissions Comparison

Each heating technology has a different carbon intensity based on its energy source: • Natural gas: Direct combustion emissions (51.4 kg CO₂/GJ for natural gas) • Electricity (grid): Victorian grid emission factor (currently ~0.85 kg CO₂/kWh, declining annually with renewable penetration) • Solar: low operating emissions, mainly affected by circulation pump electricity and the system itself Our comparison includes annual CO₂ equivalent emissions for each option, helping environmentally-conscious pool owners factor carbon impact into their decision.