What size water heater for a family of 4?
With 3 of the 4 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 4 shower back to back, demand hits 86 gallons; the table below covers every version of your mornings.
Every version of the busiest hour, for 4 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 |
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.
The tank you buy for four people serves a different four people
A water heater runs eight to twelve years, and four-person households change more inside that window than any other size. The 66-gallon hour above is built on the worksheet's ten-minute shower. Teenagers do not take ten-minute showers. At twenty minutes each on a 2.5 GPM head, two of them are 80 hot gallons on their own; add one ordinary shower and the sink use and the hour reaches 106, past every electric tank in the residential catalogue and into 75-gallon gas.
Which leaves two honest ways to size a house with small children in it. Buy for today and plan to replace early, or buy the bigger gas tank now and carry the extra standing loss for a decade. The second is usually the cheaper one, because most of what a water heater costs is the install, and a flue and a gas line sized for a 75 today do not get sized again in 2036.
A second bathroom changes the shape of the hour rather than its size. Four people with two baths shower in pairs, which puts the same 66 gallons through the tank in half the time. That outruns recovery on either fuel, so what governs is stored volume and not the first hour rating: a 50-gallon tank holds about 35 usable gallons and a simultaneous pair of showers is 40.
Questions people ask
Is a 50-gallon water heater enough for a family of 4?
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 4?
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.
Is water heater size for a family of 4 the same as for a 4-bedroom house?
No. This page sizes four people in the busiest hour. A 4-bedroom house is planned for five people (bedrooms plus one), which is a heavier morning and usually a larger tank. Use the family page when you know who lives here; use the bedroom page when you are sizing the house for whoever might live here over the tank's life.