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. That hour already counts all 3 of you, so it is the number, not a worst case; the table below shows the calmer mornings underneath it.
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.
Three people, and the shower head that picks the fuel
Three is the largest household this site plans with nobody stepping out of the way. The busiest hour above puts all three of you in the shower inside it. From four people up, the same planning rule quietly assumes somebody is already out the door. So if your three all leave at eight, the 66-gallon figure is your number and not a worst case.
On gas the hour is uneventful. A 40-gallon gas tank rates about 71 gallons in its first hour against 66 of demand, which is why builders drop a 40 into a three-person house without anybody running the arithmetic.
On electric the whole question is the shower heads. A 50-gallon electric delivers about 55 gallons in its first hour and a 65 about 66, which is the demand with nothing spare, so the honest pick is an 80. Fit 2.0 GPM heads and the hour falls to 45 gallons, inside a 40-gallon electric's 48. Same three people, same house, and the electric tank is either 40 gallons or 80 depending on hardware that costs twenty dollars.
Composition splits this size in two, more than any other. Two parents and a small child get a free pass, because a toddler's bath is at seven in the evening and never touches the morning hour. Three adults sharing a rental get no such thing: one commute, one hour, three showers.
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.