What Size Water Heater Do You Need? A Simple Sizing Guide
How to size a tank water heater by household and peak hot water use, what the first-hour rating means, and why gas and electric size differently.
In this guide
For most homes, a 40-gallon tank suits 1 to 3 people, a 50-gallon tank suits 3 to 4 people, and larger households often need 65 to 80 gallons or a tankless unit. The better measure is the first-hour rating (FHR) on the label: it should match or exceed the hot water you use in your busiest hour. Gas heaters recover faster than electric ones, so a gas tank can often be a size smaller than an electric tank for the same household.
Choosing the right size water heater is about matching it to how your household uses hot water, especially during your busiest hour. Too small and you’ll run out during morning showers; too big and you pay to keep extra water hot that you never use.
A quick sizing guide for tank water heaters
| Household | Gas tank | Electric tank |
|---|---|---|
| 1 to 2 people | 30 to 40 gallons | 40 gallons |
| 2 to 4 people | 40 to 50 gallons | 50 gallons |
| 4 to 5 people | 50 gallons | 65 to 80 gallons |
| 5+ people or heavy use | 50+ gallons, or tankless | 80 gallons, heat pump, or tankless |
These are starting points. Your actual peak-hour use matters more than headcount.
Why gas and electric size differently
A gas burner heats water much faster than electric elements, so a gas heater recovers more quickly after you use hot water. That’s why a 40- or 50-gallon gas tank can keep up with a household that might need a 50- or 65-gallon electric tank. Heat pump water heaters recover more slowly still in efficiency mode, so they’re often sized a step larger.
Use the first-hour rating, not just gallons
The first-hour rating (FHR) on the heater’s label tells you how many gallons of hot water it can deliver in an hour starting with a full tank. Estimate your busiest hour of hot water use and pick a heater with an FHR that meets or exceeds it.
- Pick your busiest hour. For most families it’s the morning rush.
- Add up the hot water uses in that hour. As rough guides, a shower often uses around 10 to 20 gallons of hot water depending on length and showerhead; a dishwasher load and a washing machine load on warm use several more gallons each.
- Compare to the FHR. Choose a heater whose first-hour rating covers that total.
Other things that affect size
- Large or soaking tubs can empty a smaller tank in a single fill.
- Space. An 80-gallon electric tank is much taller and wider than a 50; closets and attics may limit your options.
- Incoming water temperature. In winter, colder incoming water reduces effective capacity.
- Future plans, like a growing family or a basement bathroom.
When tankless makes more sense
If you’d need a very large tank or you want hot water that never runs out, a tankless heater may be a better fit, sized by flow rate instead of gallons. See tankless vs. tank water heaters.
Get an honest recommendation
We’ll look at your household, fixtures, space and fuel type and recommend the right size, not just a copy of the old heater. Estimates are free and upfront.
Replacing an aging heater? Read how long water heaters last and what affects the cost of replacing a water heater.
Key takeaways
- A 40-gallon tank suits most 1 to 3 person homes; 50 gallons suits 3 to 4.
- Use the first-hour rating to match your busiest hour of hot water use.
- Gas tanks recover faster, so they can often be a size smaller than electric.
- Big tubs, space limits and winter water temperatures all affect sizing.
- For very high demand, consider tankless or a larger electric or heat pump unit.
Frequently asked questions
What size water heater do I need for a family of four?
Usually a 50-gallon gas tank or a 50 to 65-gallon electric tank, depending on how much hot water you use in your busiest hour.
Is a bigger water heater always better?
No. An oversized tank wastes energy keeping extra water hot. Size it to your peak-hour use.
What is a first-hour rating?
It’s how many gallons of hot water the heater can supply in one hour, starting with a full tank. It’s on the label and is the best way to compare heaters.
Can I replace my 40-gallon heater with a 50?
Usually, if there’s space and the gas line, venting or electrical circuit supports it. We check those before recommending a size change.
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