Water Heater Efficiency Ratings Explained

If you’re shopping for a new water heater, the numbers on its package might look like encoded information. 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 Is Key

Heating water is one of the biggest energy drains in a home. On average, U.S. homes allocate roughly 5–7% of their annual electric bill to hot water. This equates to about $150–$200 annually for the average family. Opting for a higher-rated unit can cut that expense, shrink your carbon footprint, and usually extend its life.

Frequently Used Ratings
Annual Fuel Utilization Efficiency (AFUE)

Used for gas and oil tank water heaters.

Shown as a percent, it shows how much of the fuel’s energy goes into heating water throughout the year.

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 名古屋市東区 給湯器 修理 gas tank heaters.

It accounts for standby, cycling losses, and the overall unit efficiency.

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

They apply to electric heat pumps and air‑conditioners.

EER equals cooling output (BTU

SEER is the average EER over a typical cooling season.

In water‑heater terms, the corresponding measure is the Coil Efficiency of the heat pump; brands usually refer to it as a "COP" (Coefficient of Performance).
COP

Used 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.
Rate of Recovery

It isn’t expressed as a percent, yet it’s a crucial performance indicator.

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).

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

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

How Ratings Translate to Real Costs

Let’s break it down with a simple example. Imagine you’re comparing 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 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 to kWh (1 kWh ≈ 3412 BTU).

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

• 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 Heaters

• They continuously store hot water.

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

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

- Tankless Heaters

• Heat water on demand, 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.