While searching for a new water heater, the figures on its packaging may seem cryptic. They reveal how efficiently the heater transforms fuel into hot water, though presented in various forms. Grasping each rating’s definition, measurement, and true cost helps you make a more informed purchase.

Why Efficiency Matters

Heating water accounts for one of the biggest energy losses in a household. On average, U.S. homes allocate roughly 5–7% of their annual electric bill to hot water. It amounts to approximately $150–$200 per year for a typical household. Opting for a higher-rated unit can cut that expense, shrink your carbon footprint, and usually extend its life.

Common Efficiency Ratings
Annual Fuel Utilization Efficiency (AFUE)

Applicable to gas and oil tank heaters.

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

Example: An 80 % AFUE heater turns 80 % of the gas into hot water; the rest is lost through the vent or standby heat loss.
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.
EER and SEER

They apply to electric heat pumps and air‑conditioners.

EER measures cooling output (BTU

SEER averages EER throughout a typical seasonal cycle.

When applied to water heaters, the analogous metric is the Coil Efficiency of the heat pump, often listed 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 isn’t expressed as a percent, yet it’s a crucial performance indicator.

It indicates the speed at which a heater can elevate a specified volume of water (e.g., 50 gal) by a set °F.

hr.

Important for households with high simultaneous hot‑water demand.
Volume Capacity

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

For tankless systems, the metric is "Gallons per Minute" (GPM).

A larger capacity or GPM reduces the chance of running out of hot water during peak demand.

Interpreting Ratings as Real Costs

Let’s illustrate with a straightforward example. Assume you’re deciding between two 50‑gal electric tank heaters:

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

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

Assume your household uses 200 gal of hot water per month and your electricity rate is $0.13

1. Convert EF to annual energy consumption:

• 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. Convert gallons to 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.

Tank vs. Tankless: Which is More Efficient?

- Tank Heaters

• They continuously store hot water.

• Standby losses often rise in cold climates.

• Recovery rate constrains concurrent use; many appliances can deplete hot water.

- Tankless Heaters

• They provide hot water on demand, removing standby losses.

{• Higher EF or COP values (often 0.95–0.99 for electric, 3–4.5 COP for 名古屋市東区 エコキュート 交換 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.