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While searching for a new water heater, the figures on its packaging may seem cryptic. Efficiency ratings tell you how well the appliance turns fuel into hot water, but they come in different flavors. Understanding what each rating means, how it’s measured, and what it really costs you can help you make a smarter 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. It amounts to approximately $150–$200 per year for a typical household. Choosing a unit with a higher efficiency rating can reduce that cost, lower your carbon footprint, and 名古屋市東区 エコキュート 交換 often come with a longer lifespan.

Frequently Used Ratings
AFUE: Annual Fuel Utilization Efficiency

Applicable to gas and oil tank 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)

Serves as the contemporary alternative to AFUE for electric and gas tank heaters.

Includes standby losses, cycling losses, and the overall efficiency of the unit.

Typical EF values: 0.70–0.95. The higher, the better.
SEER

They apply to electric heat pumps and air‑conditioners.

EER measures cooling output (BTU

SEER is the average EER over a typical 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).
COP

Designed for electric heat‑pump water heaters.

It represents the ratio of heat output to electrical input.

A COP of 3 indicates that each 1 kWh of electricity yields 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.

Expressed in gallons per hour (GPH) or BTU

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

It denotes the total water volume the tank can store (in gallons).

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

High capacity or GPM means you’re less likely to run out of hot water during peak use.

How Ratings Translate to 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

Suppose your household consumes 200 gal of hot water monthly and the electric rate is $0.13

1. Convert the EF into annual energy consumption:

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

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

°F, 1°F rise ≈ 1 BTU per lb.

• It’s a rough approximation; real energy cost hinges on temperature rise, yet the savings are evident: Heater B consumes ~16 % less energy.

3. Convert to kWh (1 kWh ≈ 3412 BTU).

kWh.

• Heater B: 222.2 gal × …

The math shows that even a 15 % improvement in EF can shave $20–$30 off your monthly utility bill, adding up to $200–$300 a year.

Tank vs. Tankless – Which Is More Efficient?

- Traditional Tank Heaters

• They maintain a constant hot‑water reservoir.

• Standby losses often rise in cold climates.

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

- On‑Demand 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.