What size water heater for a family of 5 or more?
The busiest hour for 5 people is 4 showers plus sink use, which is 86 gallons: that takes a 75-gallon gas tank, and it is past every single electric tank made. All 5 in one hour is 106 gallons. Six, seven and eight people read this page too, because past five the answer stops moving with the headcount: it is a big gas tank, two tanks, a tankless sized to simultaneous flow, or a shower schedule with teeth. The table runs to eight showers so you can find your morning in it.
Every version of the busiest hour, for 5 to 8 people
Each row is that many showers in one hour plus one shave and one round of hand dishes, priced in hot gallons off the DOE/AHRI worksheet (20 per standard shower, 13 on a 2.0 GPM low-flow head). The tank shown is the smallest standard size whose first hour rating covers the demand; our FHR figures are ~70% of tank volume plus an hour of recovery, and label values land within a few gallons of them.
| Showers in the hour | Peak demand | Gas tank | Electric tank | Demand, 2.0 GPM heads | Gas | Electric |
|---|---|---|---|---|---|---|
| 1 | 26 gal | 30 gal | 30 gal | 19 gal | 30 gal | 30 gal |
| 2 | 46 gal | 30 gal | 40 gal | 32 gal | 30 gal | 30 gal |
| 3 | 66 gal | 40 gal | 80 gal | 45 gal | 30 gal | 40 gal |
| 4 | 86 gal | 75 gal | none fits | 58 gal | 40 gal | 65 gal |
| 5 | 106 gal | 75 gal | none fits | 71 gal | 50 gal | 80 gal |
| 6 | 126 gal | 75 gal | none fits | 84 gal | 75 gal | none fits |
| 7 | 146 gal | two tanks | none fits | 97 gal | 75 gal | none fits |
| 8 | 166 gal | two tanks | none fits | 110 gal | 75 gal | none fits |
Take the two low-flow columns on the right as a live option rather than a footnote. They are this same house with 2.0 GPM heads on the walls, and at this size that swap is often the whole difference between one water heater and two.
Count bathrooms before you read a row
The rows are showers in an hour, not people, and the difference decides which one is yours. Ten minutes of water plus the turnaround between two people is about twelve minutes of bathroom, so one bathroom tops out near five showers an hour and two baths near ten. A household of eight with one bathroom never reaches the eighth row; it reaches the fifth and then spills into the next hour, which is a different and easier problem.
Where the biggest tank on the floor runs out
A 75-gallon gas tank rates about 133 gallons in its first hour. Six standard showers plus sink use is 126, so it carries six and fails at seven. That is the end of the residential catalogue on a single tank, and no amount of shopping moves it.
The low-flow column reads differently, and this is the part worth acting on. Seven 2.0 GPM showers plus sink use is 97 gallons and eight is 110, both comfortably inside that one 75-gallon gas tank. For a seven or eight person house, the shower head is the difference between one water heater and two.
Electric, at this size
Past three showers an hour the electric column is empty and it stays empty. An 80-gallon element puts back about 20 gallons an hour, so an electric house here is buying storage rather than recovery, and 76 gallons of first hour rating on the biggest tank made is all the storage there is. Your options: two tanks, an 80-gallon heat pump unit switched to its high-demand mode so the resistance elements carry the peak, or a schedule somebody actually enforces.
Two tanks, and the pipe feeding them
Plumbed in series the first tank preheats the second, and the pair delivers close to the sum of their first hour ratings. Two 50-gallon gas units often cost less installed than one 75 plus the flue work the 75 needs, and they fit through a basement door that the 75 does not. Plumbed in parallel they split the draw evenly, which is the better answer when the house has two bathing clusters at opposite ends.
Either way, look at the gas supply before the tank. A 75,000 BTU heater is not a drop-in for a 40,000 BTU one, and two tanks plus a furnace and a range on one half-inch branch will outrun the pipe well before it outruns the meter. The symptom is not a cold shower. It is a burner that will not stay lit when the furnace calls, in February, and the fix is a permit and a pipe.
Questions people ask
Is a 50-gallon water heater enough for a family of 5?
Not on its own. 4 showers plus sink use is 86 gallons, and a 50-gallon tank delivers about 78 (gas) or 55 (electric) gallons in the hour. A 50 works here only if the household genuinely spreads showers across the day.
Do these numbers change with teenagers?
Only in the honest direction. The worksheet's 20-gallon shower is a 10-minute shower on a 2.5 GPM head; a teenager's 25-minute shower is 50 gallons all by itself. If that is your house, count long showers as two.
What about a tankless for a family of 5?
It sidesteps the peak-hour problem entirely, because a tankless never runs out; it just caps how many fixtures run at once. See the tankless answer for this household.