What size water heater for a family of 2?
With 2 of the 2 showering in the same hour on standard heads, peak demand is 46 gallons: a 30-gallon gas tank covers it, electric needs 40 gallons. Low-flow heads pull the electric answer down to 30 gallons. That hour already counts all 2 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 2 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 |
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.
Two people, and the twenty minutes an hour rating hides
A first hour rating measures an hour. A couple does not shower across an hour. Two people leaving the house together draw 40 gallons in about twenty minutes, and inside that window nothing is feeding the tap but stored water. A tank gives up roughly 70% of its volume before the outlet cools, so a 40-gallon tank has about 28 usable gallons in it and the second shower turns lukewarm around the eight-minute mark, even though the same tank's 48-gallon electric first hour rating says the morning is comfortable. Fifteen minutes of stagger and it never happens.
The other lever is what is screwed onto the shower arm. Two standard heads plus sink use is 46 gallons; two 2.0 GPM heads is 32. That one swap moves the electric answer from a 40-gallon tank to a 30, and it is the cheapest sizing decision on this site.
Where couples get it wrong is buying for exactly today. A 30-gallon electric fits two people who shower twelve hours apart and nobody else, ever. Add a house guest, or a partner who starts working nights, and the sixty dollars saved is why the shower ran cold in front of company.
Questions people ask
Is a 50-gallon water heater enough for a family of 2?
Yes, generously. A 50-gallon gas tank delivers about 78 gallons in its first hour and a 50 electric about 55, both past the 46-gallon hour two people can realistically pull. You could buy smaller; nobody regrets a 50.
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 2?
Feasible and usually oversized for the need; a small unit does fine. Size it to simultaneous draw with the tankless calculator, not to this page's gallons.