What Size Water Heater Does Your Family Need?

A household of 1–2 people usually needs a 30–40 gallon tank. A family of 3–4 usually needs a 40–50 gallon tank. A family of 5 or more usually needs a 50–80 gallon tank or a properly sized tankless unit.

But tank size alone is not the number that decides whether you run out of hot water. The number that matters most is the first hour rating (FHR), and it should match or beat your household’s busiest hour of hot water use.

Quick Water Heater Size Chart

Use this chart as a starting point. Then use the peak-hour method below to confirm it.

Notice that electric and heat pump units are sized larger than gas for the same family. That is because they reheat water more slowly. We explain why below.

Why Tank Size Is Not the Whole Story

A tank’s gallon number tells you how much water it holds. It does not tell you how much hot water it can deliver when everyone is using it at once.

The first hour rating does. FHR is the number of gallons of hot water a fully heated tank can deliver in one hour of heavy use. It combines two things:

• How much hot water is already stored in the tank
• How fast the burner or heating element can reheat new cold water coming in

Two 50-gallon tanks can have very different FHRs. A gas model with a strong burner may deliver 80 gallons or more in the first hour. A standard electric model of the same size may deliver closer to 60. If your family’s busiest hour needs 70 gallons, one of those tanks works and the other leaves someone in a cold shower.

You can find the FHR on the yellow EnergyGuide label on the side of any new tank water heater. The U.S. Department of Energy recommends matching this number to your household’s peak-hour demand.

How to Find Your Family’s Peak-Hour Demand

Your peak hour is the single busiest hour of hot water use in your home. For most families, it is a weekday morning. For some, it is the evening when showers, dishes, and laundry overlap.

Follow these three steps.

Step 1: Pick your busiest hour

Think about a normal weekday. When do the most people shower? When does the dishwasher run? Does anyone start laundry before work? Write down everything that uses hot water in that one hour.

Step 2: Add up the gallons

Use these average hot water amounts from the Department of Energy’s sizing worksheet:

Example: A family of four has three showers, one hand dishwashing session, and one dishwasher cycle in the same morning hour.

• 3 showers × 20 = 60 gallons
• 1 hand dishwashing × 3 = 3 gallons
• 1 dishwasher × 7 = 7 gallons
• Peak-hour demand = 70 gallons

Step 3: Match the first hour rating

This family needs a water heater with an FHR of at least 70 gallons. A 40-gallon gas tank may come close, but it will likely fall short on busy mornings. A 50-gallon gas tank with an FHR in the 80s would handle this household comfortably.

How Fuel Type Changes the Right Size

The type of water heater you choose has a big effect on sizing. This is where many homeowners make mistakes.

Gas and propane tanks reheat water fastest. Because they recover quickly, a smaller gas tank can often keep up with the same family that needs a larger electric tank.

Standard electric tanks reheat more slowly. Most families switching from gas to electric need to go up one size to keep the same hot water performance.

Heat pump (hybrid) water heaters are the most energy-efficient tank option, and ENERGY STAR certifies many models. In their most efficient setting, they recover even more slowly than standard electric tanks. Families switching to a heat pump unit should usually size up, often to 65 or 80 gallons for a family of four or more. Heat pump units also need enough surrounding air space to work properly, so the location matters as much as the size.

Tankless water heaters do not store water at all. They are sized by flow rate instead of gallons. That process is different, so we cover it next.

How to Size a Tankless Water Heater in Yolo County

A tankless unit heats water as it flows through. Its size is measured in gallons per minute (GPM) at a certain temperature rise. Temperature rise is how many degrees the unit must heat the incoming cold water.

Step 1: Know your incoming water temperature

This step is where local conditions matter. Since 2016, most homes in Woodland and Davis get their water from the Sacramento River through the Woodland-Davis Clean Water Agency. River water changes temperature with the seasons more than deep groundwater does. In the coldest months, incoming water can drop into the upper 40s °F.

For safe sizing in Woodland and Davis, plan around roughly 50°F incoming water in winter.

Step 2: Figure out your temperature rise

The U.S. Consumer Product Safety Commission recommends setting water heaters at 120°F to lower the risk of scalding. If your incoming water is 50°F and your setpoint is 120°F, your unit needs a 70°F temperature rise.

Step 3: Add up your peak flow rate

Add the flow rates of every hot water fixture that could run at the same time. California limits new fixture flow rates, which helps keep tankless sizing manageable:

• Showerheads: 1.8 GPM maximum under California rules
• Kitchen faucets: 1.8 GPM maximum
• Bathroom faucets: 1.2 GPM maximum

Example: Two showers (3.6 GPM) plus a kitchen faucet (1.8 GPM) = 5.4 GPM.

This family needs a tankless unit that can deliver at least 5.4 GPM at a 70°F rise. Check the manufacturer’s flow chart, not just the maximum GPM on the box. The box number is often measured at a much smaller temperature rise and will overstate what the unit can do in a Yolo County winter.

Older homes may still have showerheads that flow 2.5 GPM or more. Count what is actually installed, not what code allows today.

Before You Upsize: Check for Sediment First

Here is something many homeowners in Woodland and Davis miss. If your water heater used to be enough and now runs out of hot water faster, the tank may not be too small. It may be losing space to sediment.

Before 2016, Woodland’s groundwater averaged about 18 grains per gallon of hardness. According to the City of Woodland, today’s surface water averages about 4 grains per gallon. Tanks installed during the groundwater years often have a thick layer of mineral sediment on the bottom. That layer takes up space, insulates water from the burner, and slows recovery.

Warning signs of sediment buildup include:

• Popping or rumbling sounds while the heater runs
• Hot water that runs out sooner than it used to
• Rusty or cloudy hot water
• A tank that is 10 or more years old

If these sound familiar, have the tank inspected before buying a larger one. Our water heater repair team can tell you whether flushing, repair, or replacement makes more sense. You can also read more about how hard water damages your plumbing.

Homes on private wells in rural Yolo County may still have very hard water. Those tanks build sediment faster and need more frequent maintenance.

The Risks of Getting the Size Wrong

Sizing is not only about comfort. A poorly sized water heater can create safety and performance problems.

An undersized heater leads to cold showers and frustration. It also tempts homeowners to turn the thermostat up to stretch the hot water supply. This is a real scald risk, especially for young children and older adults. Hotter water also speeds up sediment buildup and wear on the tank.

An oversized heater keeps more water hot than you use. That means more heat lost while the water sits. A larger tank can also bring code changes. It may need a larger gas line, different venting, a new electrical circuit, or more floor space than your current closet or garage allows.

Any tank replacement in California must follow state safety rules. California Health and Safety Code Section 19211 requires all residential water heaters to be braced, anchored, or strapped to resist earthquake motion. Code calls for two straps, one in the upper third and one in the lower third of the tank. Gas water heaters in garages also generally need their burner raised at least 18 inches off the floor to reduce the risk of igniting fumes from cars, gas cans, or solvents. A larger tank that does not fit these requirements in your current space is not a safe choice.

Signs Your Current Water Heater Is the Wrong Size

Your current unit may be undersized if:

• Hot water runs out during the same routine every day
• The last person to shower always gets lukewarm water
• You have to space out showers, dishes, and laundry to avoid running out
• Your family has grown since the heater was installed

Your current unit may be oversized if:

• You rarely use more than a fraction of the tank
• Only one or two people live in a home that once had a large family

Frequently Asked Questions

Is a 40-gallon water heater enough for a family of 4?

Sometimes. A 40-gallon gas tank with a strong first hour rating can work for a family of four that spreads out showers. If three or more people shower in the same hour, a 50-gallon tank is usually the safer choice. A family of four with an electric tank should generally start at 50 gallons.

Should I get a 40 or 50 gallon water heater?

Compare first hour ratings, not just tank sizes. If your peak-hour demand is under about 60 gallons, a 40-gallon gas tank may work. If it is 60 gallons or more, choose a 50-gallon tank. Going with the larger tank also gives you room if your household grows.

What size tankless water heater do I need for a family of 4?

Most families of four need a tankless unit that delivers 5 to 7 GPM at a 70°F temperature rise in Woodland and Davis winters. The exact number depends on how many showers and faucets run at the same time.

Where do I find my water heater’s first hour rating?

Look at the yellow EnergyGuide label on the side of the tank. The FHR is listed as “Capacity (first hour rating).” If the label is missing on an older unit, the model number can be used to look it up.

Does a bigger water heater mean hotter water?

No. Tank size controls how much hot water is available, not how hot it gets. Temperature is set by the thermostat. Keep it at 120°F unless a plumber advises otherwise.

Get Help Sizing Your Next Water Heater

Choosing a water heater size is easier with someone who has installed thousands of them in Yolo County homes. Yolo Plumbing Inc. installs gas, propane, electric, tankless, and heat pump water heaters from plumbing-grade brands like State and Bradford White. We will look at your household, your space, your gas or electric service, and your current setup before recommending a size.

Learn more about our water heater installation and tankless water heater services, or visit our water heaters page.

Yolo Plumbing Inc. has been family owned in Yolo County since 2011 and has been voted best plumbing company in Yolo County by The Davis Enterprise and The Daily Democrat since 2013. We serve Woodland, Davis, Winters, and surrounding Yolo County communities.

Want it to flow…and service from a pro? Call Yolo Joe at or schedule online.