What size water heater for 5 people?
For 5 people, the usual answer is 60 to 66 gallons — but the number that actually matters is first hour rating, not tank volume.
This is an estimate from the standard industry rule of thumb, not an engineering calculation. For anything you are about to spend money on, have the figure confirmed by a load calculation.
5 people: the numbers
| Measure | Value |
|---|---|
| Storage tank size | 60 to 66 gallons |
| First hour rating to look for | 75 to 85 gallons |
| Tankless flow rate | 7 to 8 GPM |
First hour rating is the tank volume plus whatever the burner or element can reheat within that hour, and it is the figure that decides whether the last person gets a cold shower. A 40 gallon tank with a strong gas burner routinely out-delivers a 50 gallon electric one, which is why comparing tanks by gallons alone leads people to buy the wrong thing.
Household size is only a proxy for peak demand. 5 people who all leave the house at eight in the morning need more capacity than 5 people on staggered schedules. If your household bunches up, size against the next tier up and what size water heater for 5 people with that in mind.
Tank or tankless
Tankless changes the question from gallons to gallons per minute, and from storage to temperature rise. A unit that comfortably supplies 7 to 8 GPM in a warm climate can fall well short of that in winter, because incoming water at 4°C needs roughly twice the energy to reach shower temperature as water at 18°C. Size a tankless unit for your coldest month, not for an annual average.
The other consideration is simultaneity. A tank does not care how many fixtures run at once until it empties; a tankless unit cares immediately, because flow rate is shared. For 5 people, that usually means deciding whether two showers ever run at the same time.
Recovery rate is the third number worth knowing, and it is where gas and electric diverge sharply. A gas tank reheats roughly two to three times faster than an electric one of the same volume, which is why a 40 gallon gas heater and a 50 gallon electric heater often carry a similar first hour rating. If you are switching fuel type, comparing tanks by gallons alone will mislead you in one direction or the other.
Finally, consider where the heater sits. A tank in an unheated garage or basement loses heat to the space around it continuously, and in a cold climate that standby loss is real money over a fifteen year life. An insulating blanket on an older tank pays for itself quickly; newer tanks are usually well enough insulated that adding one gains little.
Where a rule of thumb stops being enough
Every number on this page comes from the standard industry rule of thumb, and a rule of thumb is not an engineering calculation. The real method is a Manual J load calculation, which models your wall and attic insulation, your window area and orientation, how leaky the building envelope is, and how much your ducts lose. It routinely lands a size away from any square-footage estimate — in either direction, which is the part people forget.
So treat this as a sanity check rather than a specification. Ten minutes to what size water heater for 5 people tells you whether a quote is in the right neighbourhood, which is genuinely useful — it is enough to catch a contractor who has quoted you two sizes up because that is what was on the truck. It is not enough to order equipment from.
Tankless changes the question entirely. Instead of gallons you size by flow rate in gallons per minute and by temperature rise, and cold incoming water in winter can halve the flow a unit can support. A tankless heater that is generous in Florida is undersized in Minnesota.