When you’re looking to buy a new water heater, the numbers on the packaging can feel like a secret code. These ratings indicate how effectively the device converts fuel into hot water, yet they vary in type. Knowing the meaning, measurement, and actual cost of each rating can guide you to a wiser choice.

The Importance of Efficiency

Water heating ranks among the largest energy consumers in a residence. A typical U.S. household spends about 5–7% of its yearly electricity bill on hot water. That translates to roughly $150–$200 a year for a typical family. 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)

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)

It supersedes AFUE for electric and gas tank units.

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

Common EF ranges: 0.70–0.95—higher values indicate better efficiency.
Energy Efficiency Ratio (EER) and Seasonal Energy Efficiency Ratio (SEER)

These are for electric heat pumps and air‑conditioning units.

EER equals cooling output (BTU

SEER represents the mean EER across a standard cooling season.

For water heaters, the equivalent metric is the Heat‑pump 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.

A COP of 3 means that for every 1 kWh of electricity, the heater delivers 3 kWh of hot water energy.
Recovery Rate

Not a percentage, but a key performance metric.

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

hr.

Important for households with high simultaneous hot‑water demand.
Capacity of the Tank

It’s the maximum water volume the tank can contain (in gallons).

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

High capacity or 名古屋市東区 エコキュート 交換 GPM means you’re less likely to run out of hot water during peak use.

Interpreting Ratings as Real Costs

Let’s break it down with a simple 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

kWh.

1. Convert the EF into 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 using 1 gal ≈ 8.34 lb, 1 lb ≈ 1 BTU

• This is a ballpark figure; actual cost varies with temperature rise, but the comparative savings are obvious: Heater B uses roughly 16 % less energy.

3. Convert to kWh (1 kWh ≈ 3412 BTU).

kWh.

• Heater B: 222.2 gal × …

The math reveals that a 15 % EF increase can reduce your monthly utility bill by $20–$30, which adds up to $200–$300 per year.

Comparing Tank and Tankless Water Heaters for Efficiency

- Tank‑Based Heaters

• They maintain a constant hot‑water reservoir.

• Standby losses can be high, especially 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 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.