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While searching for a new water heater, the figures on its packaging may seem cryptic. These ratings indicate how effectively the device converts fuel into hot water, yet they vary in type. Grasping each rating’s definition, measurement, and true cost helps you make a more informed purchase.

The Importance of Efficiency

Heating water accounts for one of the biggest energy losses in a household. A typical U.S. household spends about 5–7% of its yearly electricity bill on hot water. This equates to about $150–$200 annually for the average family. Selecting a unit with a better efficiency rating may lower costs, reduce your carbon impact, and often increase longevity.

Common Efficiency Ratings
AFUE: Annual Fuel Utilization Efficiency

Used for gas and oil tank water heaters.

Presented as a percentage, it indicates the portion of fuel energy that heats water annually.

Take an 80 % AFUE heater: it uses 80 % of the gas for heating, with the remaining energy vented or lost in standby.
Energy Factor (EF)

The modern replacement for AFUE for electric and gas tank heaters.

Incorporates standby losses, cycling losses, and the total efficiency of the heater.

Typical EF figures: 0.70–0.95; the greater the number, the superior the efficiency.
SEER

They apply to electric heat pumps and air‑conditioners.

hr) to electric input (W).

SEER represents the mean EER across a standard cooling season.

For water heaters, the equivalent metric is the Coil Efficiency of the heat pump; manufacturers often quote it as a "COP" (Coefficient of Performance).
Coefficient of Performance (COP)

Designed for electric heat‑pump water heaters.

It’s a ratio of heat energy delivered to electrical energy consumed.

With a COP of 3, every 1 kWh of electricity produces 3 kWh of hot‑water energy.
Recovery Rate

It’s not a percentage, but it remains a vital performance metric.

It shows how fast a heater can heat a fixed volume (e.g., 50 gal) by a given degree rise.

It’s measured in GPH or BTU

Crucial for 名古屋市東区 エコキュート 交換 homes with high concurrent hot‑water usage.
Volume Capacity

The total amount of water the tank can hold (in gallons).

Tankless units use "Gallons per Minute" (GPM) to describe capacity.

Greater capacity or GPM lowers the risk of depleting hot water during high‑usage periods.

Interpreting Ratings as Real Costs

We’ll simplify it with a basic example. Suppose you’re choosing between two 50‑gal electric tank heaters:

• Heater A: EF = 0.75, Recovery = 40 GPH

• Heater B: EF = 0.90, Recovery = 70 GPH

If your home uses 200 gal of hot water each month and the electricity cost is $0.13

1. Translate EF into yearly energy usage:

• Heater A consumes 200 gal ÷ 0.75 = 266.7 gal‑equivalent energy units.

• Heater B consumes 200 gal ÷ 0.90 = 222.2 gal‑equivalent energy units.

2. Translate gallons into BTU (1 gal ≈ 8.34 lb, 1 lb ≈ 1 BTU

• This is a rough estimate; actual energy cost depends on the temperature rise, but the relative savings are clear: Heater B uses about 16 % less energy.

3. Convert the BTU figure to kWh using 1 kWh ≈ 3412 BTU.

• Heater A: 266.7 gal × 8.34 lb × ΔT ÷ 3412 BTU

• Heater B: 222.2 gal × …

The calculations demonstrate that a 15 % EF boost can cut $20–$30 from your monthly bill, totaling $200–$300 annually.

Comparing Tank and Tankless Water Heaters for Efficiency

- Tank Heaters

• They maintain a constant hot‑water reservoir.

• Standby losses can be high, especially in cold climates.

• Recovery rate restricts simultaneous use, risking hot‑water depletion when multiple appliances run.

- On‑Demand Heaters

• They heat water as needed, eliminating standby losses.

{• Higher EF or COP values (often 0.95–0.99 for electric, 3–4.5 COP for heat pumps).|• They usually boast higher EF or COP (often 0.95–0.99 for electric, 3–4.5 COP for heat pumps).|• They typically achieve higher EF or COP (usually 0.