Plumbing
Water heater operating cost comparison
Compare supplied delivered heat demand and efficiencies across fuels.
Your inputs
Complete the fields for your selected method. Zero means intentionally zero, not unknown. Currency selection labels amounts; it does not convert exchange rates.
How this calculation works
input energy=delivered heat/efficiency; cost=input*unit rate. Metered alternative: annual system cost = separately measured or supplied annual purchased input kWh × matching price.
Input ratio may exceed one for a heat pump COP. Convert fuel price to currency per kWh of purchased input before entry; no implicit gas-volume or fuel heat-content assumption. Delivered heat and efficiency are supplied; no heater sizing or temperature prescription.
What information do I need?
Use records for the same job, equipment or accounting period. Only the fields for your selected entry method are required. An unknown amount is not zero.
Input definitions and where to find them
- How do you know the energy use?: Choose the information you actually have. Only the selected method is required.
- Annual delivered hot-water heat (kWh thermal/year): Delivered hot-water thermal energy from isolated measurement/qualified assessment. A whole utility bill is NOT automatically delivered heat. Used with: Measured input power and operating schedule.
- Supplied heating alternatives: One row per distinct supplied heating alternatives, on the stated row and period basis. Do not enter both components and their total. Used with: Measured input power and operating schedule.
- Delivered heat / purchased input (ratio): Supplied delivered-heat/purchased-input ratio at comparable conditions; heat-pump COP may exceed one.
- Purchased energy price per kWh input (selected currency): Price per kWh of purchased input; fuel-volume prices need an explicitly supplied heat-content conversion.
- Matching-service heating input readings: Use an isolated record or clearly labeled estimate matching this field and period. Do not substitute an unrelated whole-site total. Used with: Metered or separately estimated kWh.
- Annual purchased input energy (kWh): Use matching records or a clearly identified estimate for the stated scope and period.
- Price per purchased input kWh (selected currency): Use matching records or a clearly identified estimate for the stated scope and period.
Use the Where to find this value controls beside the inputs for available work-it-out helpers. Estimates remain your assumptions; a helper does not verify the source figures.
Worked example
Example amounts use US dollars (USD).
Example answer: System 1 annual purchased energy is 11,111.11 kWh input/year for the illustrative inputs below.
Example inputs
- How do you know the energy use?: Measured input power and operating schedule
- Annual delivered hot-water heat: 10,000.00 kWh thermal/year
- Supplied heating alternatives
- Delivered heat / purchased input: 0.90 ratio
- Purchased energy price per kWh input: $0.10
- Delivered heat / purchased input: 3.00 ratio
- Purchased energy price per kWh input: $0.20
- System 1 annual purchased energy
- 11,111.11 kWh input/year
- System 1 annual energy cost
- $1,111.11
- System 2 annual purchased energy
- 3,333.33 kWh input/year
- System 2 annual energy cost
- $666.67
These illustrative values are not recommended rates or industry averages. Replace every example input with your own figures.
Use the result well
Compare supplied delivered heat demand and efficiencies across fuels. Some modes require specialist measurements or a qualified equipment/energy estimate. If you do not have those inputs, use a directly measured alternative where offered; do not guess from unrelated bills or equipment ratings.
Keep inputs on the same scope and time basis. Calculations retain precision internally; displayed values generally round to two decimal places, with extra precision for very small values and whole-unit rounding where required. Economic comparisons describe your supplied assumptions and do not guarantee future results.
This tool provides business arithmetic. It does not approve engineering designs, establish legal or tax treatment, select equipment or certify safe operating conditions.