The First Hour Rule: How to Size and Install a 50–60 Gallon Water Heater That Actually Keeps Up

👋 Tony Here, And We're Talking First Hour Ratings

Let me ask you something: ever run out of hot water halfway through a shower just as your kid yells “I flushed the toilet!” and the dishes are running too?

Yeah. That’s not just bad timing—it’s bad water heater sizing.

I’ve been on hundreds of calls where folks thought, “50 gallons is 50 gallons, right?” Not exactly. That’s where the First Hour Rating comes in. If you’re installing a 50–60 gallon electric water heater and want it to keep up, not just sit there heating up again, this blog is for you.

Let’s talk about how to size it right, install it clean, and never hear the words “there’s no hot water” again. 😎🚿

 

🔢 Section 1: What Is the First Hour Rating (And Why Should You Care)?

The First Hour Rating (FHR) tells you how much hot water (in gallons) your water heater can deliver in the first hour of use—starting from a full tank. It combines stored hot water with how fast the unit can heat incoming cold water.

A 50-gallon tank might have an FHR of 60 to 80 gallons depending on:

• Wattage of the heating elements

• Insulation and efficiency

• Recovery rate (how fast it reheats cold water)

Let me break it down:
If you’ve got a 50-gallon tank and it refills 16 gallons in an hour, your FHR is 66 gallons. That’s how much hot water you’ll have before it runs cold.

Want to see a full breakdown? The U.S. Department of Energy explains it well here.

 

🏠 Section 2: How Much Hot Water Does Your Household Actually Use?

Here’s a rough estimate for a typical family of four during peak morning hours:

• Shower (10 min): 20 gallons per person

• Dishwasher: 6 gallons

• Handwashing/other use: 10 gallons

• Washing machine (warm cycle): 15–20 gallons

That’s easily 80–100 gallons in one hour.

So, that “50-gallon tank” won’t cut it unless it has a high enough First Hour Rating—or unless your family takes turns like they’re in a 1960s military barracks. 🫠

Need help calculating your peak demand? Rheem has a handy calculator that can give you a personalized estimate.

 

🔍 Section 3: Sizing a 50–60 Gallon Heater the Right Way

Now that you know your First Hour Rating needs, here’s how to match it with the right tank:

Here’s the key: Don’t just go by gallon size—go by FHR.
Two 50-gallon heaters might have very different performance depending on their wattage and recovery rate.

Want a selection that includes efficient, high-performance models? I trust this collection from The Furnace Outlet—good mix of power, price, and reliability.

 

🧰 Section 4: Installing It Right (Tony’s Proven Process)

Got the right unit? Good. Let’s make sure you install it like a pro—or at least like a tech who doesn’t want to get called back the next day.

Step-by-step install checklist:

1. Kill the Power. Flip the 240V breaker and test with a multimeter.

2. Drain the Old Tank. Hook up a hose and vent it by opening a nearby faucet.

3. Disconnect Plumbing and Electrical. Take pictures if you’re nervous.

4. Move In the New Unit. Don’t forget to level it with shims.

5. Hook Up the Plumbing. Use Teflon tape and dielectric unions.

6. Reconnect Electrical. Ground it properly and tighten those connections.

7. Fill the Tank Before Powering On. Or you’ll fry the elements (rookie move).

8. Check for Leaks and Fire It Up. Turn on the breaker, wait 45–60 mins.

Need visual help? This installation video by The Excellent Laborer walks through a similar process.

 

🧪 Section 5: Troubleshooting a Heater That Can’t Keep Up

If you already installed your tank and it’s still struggling, don’t panic. There could be some simple fixes:

• Wrong thermostat settings
  Check that both upper and lower thermostats are set to 120°F. Cranking it to 140 won’t heat faster—it just burns more energy.

• Only one element working
  Use a multimeter to test continuity on both elements. No continuity = time for a replacement.

• Sediment buildup
  Especially in hard water areas, this can insulate the element and reduce output. Drain and flush annually.

Check out this practical guide on flushing sediment from your tank from This Old House. Worth the read.

 

⚡ Section 6: Don’t Forget Electrical Requirements

A lot of underperformance comes down to bad wiring. Your 50–60 gallon electric water heater should be on:

• A dedicated 240V circuit

• A 30-amp double pole breaker

• 10/2 NM cable or appropriate gauge wire

Bad connections or an undersized breaker can cause heating elements to cut out early or not run at full wattage.

💡 Section 7: Tony’s Pro Tips for Never Running Out Again

Let me leave you with a few golden nuggets from years in the field:

• Go bigger if your panel can handle it. A 60-gallon high-efficiency model often costs just a little more than a basic 50.

• Install a timer or demand switch. If your water heater has long downtimes, this saves energy and keeps the tank full when you need it.

• Add a mixing valve. You can set the thermostat higher and still deliver safe, usable temps—extending your available hot water without changing the tank.

• Flush annually. Sediment is your tank’s worst enemy.

 

👋 Tony’s Wrap-Up

Alright, if you made it this far, you’re serious about getting the right water heater for your home—and I respect that. 👊

Remember: FHR > Tank Size. You can slap a 60-gallon tank in your utility closet, but if it’s slow to recover or wired wrong, you’ll still run cold.

If you’re looking to buy one that’ll actually keep up, I recommend starting with The Furnace Outlet’s 50–60 gallon lineup. I’ve installed those models more times than I can count, and they hold up.

Got more questions? Bookmark this blog, save the links, and don’t be afraid to call in a pro when you’re stuck.

Is your new 50-60 gallon water heater cold? Visit my guide: Here's Why Your Electric Water Heater Isn't Heating.

Stay safe, stay warm, and don’t let cold showers ruin your morning.
– Tony the Trusted Tech🧰🔥