What size water heater for a family of 3?
With 3 of the 3 showering in the same hour on standard heads, peak demand is 66 gallons: a 40-gallon gas tank covers it, electric needs 80 gallons. Low-flow heads pull the electric answer down to 40 gallons. If all 3 shower back to back, demand hits 66 gallons; the table below covers every version of your mornings.
Every version of the busiest hour, for 3 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 |
Laundry note: a hot-wash load adds 32 gallons to the hour, which moves every verdict in the table up a row or two. Warm and cold cycles barely register, and that is the cheapest sizing fix there is: wash on warm outside shower hour and buy the smaller tank.
Questions people ask
Is a 50-gallon water heater enough for a family of 3?
Gas, yes: its first hour rating (about 78 gallons) clears the 66-gallon hour that 3 showers plus sink use pulls. Electric, only with 2.0 GPM heads: a 50 electric delivers about 55 gallons, under the standard-head demand but over the 45-gallon low-flow version.
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 3?
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.