How to Size Your State Water Heater: BTUs, Gallons & First Hour Rating

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Choosing the right water heater size is one of the most critical steps to ensuring consistent hot water without overspending on unnecessary capacity. Whether you’re considering a State tank, gas, electric, or tankless water heater, this guide will help you understand BTUs, gallons, and First Hour Rating (FHR) to select the best model for your home.

🔍 Why Correct Sizing Matters

Avoiding Cold Showers and Inconsistent Supply

An undersized water heater will struggle during peak demand, leaving family members with cold showers or forcing you to stagger appliance use.

Avoiding Overspending

Oversizing leads to higher upfront and operating costs without additional benefit, wasting energy and money.

Optimizing Energy Efficiency

Correctly sized heaters run efficiently, reducing standby heat loss and minimizing energy bills.

Learn more about the impact of water heater sizing at Energy.gov.

🔧 Key Sizing Factors: BTUs, Gallons, and FHR

What Are BTUs?

British Thermal Units (BTUs) measure the heating power of gas water heaters. Higher BTUs = faster recovery times.

Gallon Capacity

Refers to the physical volume of water a tank can hold, typically 30-80 gallons for residential units.

First Hour Rating (FHR)

The FHR tells you how many gallons of hot water the unit can supply in an hour when fully heated, accounting for both tank capacity and recovery rate. FHR is more important than gallons alone for real-world performance.

🛁 Calculating Your Home’s Hot Water Needs

Estimate your peak hour demand:

Shower: 10 gallons
Shaving: 2 gallons
Hand dishwashing: 4 gallons
Automatic dishwasher: 6 gallons
Clothes washer: 7 gallons

Example: A family of 4 taking showers, running the dishwasher, and doing laundry simultaneously may need 50-60 gallons in the first hour.

Use AHRI Directory to find the FHR of specific State models you are considering.

🔥 Sizing Gas State Water Heaters: BTUs and Recovery Rates

BTUs and Recovery Rate

30,000 - 50,000 BTUs typical for residential gas water heaters.
Higher BTUs = faster recovery after heavy use.

Climate Factor: Homes in colder climates may need slightly higher BTUs to offset lower incoming water temperatures.

⚡ Sizing Electric State Water Heaters: Gallons and Recovery Time

Electric water heaters generally have slower recovery times, making accurate sizing critical:

30-40 gallons for 1-2 people
40-50 gallons for 3-4 people
50-80 gallons for 5+ people

FHR is critical for electric models to ensure sufficient hot water during peak use.

🚿 Sizing State Tankless Water Heaters: GPM and Temperature Rise

Gallons Per Minute (GPM)

Determine the combined GPM of appliances you expect to run simultaneously:

Shower: 2.5 GPM
Dishwasher: 1.5 GPM
Washing machine: 2.0 GPM

For two showers and a dishwasher, you would need a unit with 6.5 GPM at your desired temperature rise.

Temperature Rise

Calculate the difference between incoming water temperature and your desired output. For example:

Incoming water: 50°F
Desired output: 120°F
Required temperature rise: 70°F

Use State’s sizing calculators or consult your installer for exact sizing for tankless systems.

For more on tankless sizing: Energy Star - Tankless Water Heaters

🏠 Sizing for Future-Proofing

If you plan to:

✅ Add family members
✅ Renovate with new bathrooms
✅ Install high-demand fixtures (large tubs, rain showers)

Consider sizing up within reason to avoid needing another replacement soon while still maintaining efficiency.

❌ Common Sizing Mistakes to Avoid

⚠️ Choosing based on price alone without assessing needs.
⚠️ Ignoring peak hour demand.
⚠️ Failing to account for climate and plumbing layout.
⚠️ Oversizing dramatically, leading to wasted energy.