Tank vs tankless for a family of 6
The honest number first: six people running three showers at the same instant is 7.5 GPM, not the 15 to 25 GPM that circulates on plumbing blogs. That inflated figure is peak-hour gallons wearing the wrong units, and it hides the one fact that decides this household: even 7.5 GPM is past a single residential gas tankless in a US winter.
The instant a family of 6 actually hits
Three simultaneous showers on standard 2.5 GPM heads is 7.5 GPM. To make that water a tankless has to add 500 × 7.5 × the rise in BTU every hour. At a northern 70°F rise that is 262,500 BTU/hr of delivered heat, which needs about 320,122 BTU/hr of gas input, past the 199,000 BTU residential ceiling. The biggest single unit made delivers only about 4.7 GPM at that rise, not even two showers. Move the house to the Gulf coast and the rise drops to 48°F, but 7.5 GPM still needs 219,512 BTU/hr of input, still past one unit. Three showers at once is a two-unit draw almost anywhere.
Where the inflated number comes from
Take the busiest hour instead of the instant. Five practical showers in the morning plus a shave and a round of hand dishes is about 106 gallons of hot water across 60 minutes. Someone divides a big hourly total by a short window, or just quotes the gallons as if they were flow, and out comes "a family of 6 needs 15 to 25 GPM." It is the right idea about size pointed at the wrong unit. Gallons per hour sizes a tank; gallons per minute sizes a tankless, and the two numbers are not interchangeable.
What actually fits six people
A 75-gallon gas tank (first hour rating about 133 gallons) covers that 106-gallon hour on stored gallons, and it does not care whether the showers overlap. That is the tank's whole trick: it hides simultaneity. If you want tankless for a family of six, the honest plan is two units manifolded together, or one unit with a shower schedule the household will actually keep. What does not exist is the single tankless that quietly serves three simultaneous showers in January.
Sizing a tankless for six (plan on two units for three simultaneous showers)? Shop tankless water heaters on Amazon (sponsored)
Questions people ask
Is a tankless water heater worth it for a family of 6?
It can be, but not as one unit sized to a made-up number. Six people running three showers at once is 7.5 GPM, and that instant is past a single residential gas tankless at every US winter inlet, even on the Gulf coast. A family of 6 that wants tankless plans on two units or a firm shower schedule; a family that showers in relays gets tankless's real advantage, never running out across a long morning.
How many GPM does a family of 6 really need?
About 7.5 GPM at the worst instant, three showers at 2.5 GPM each. The 15 to 25 GPM you will see quoted is a peak-hour gallons number in the wrong units. If your family never runs three showers at the same second, size to the moment you actually hit; the decision tool takes any combination.
What size tank does a family of 6 need instead?
A 75-gallon gas tank covers the roughly 106-gallon busiest hour on stored gallons, no matter how the showers overlap, because a tank hides simultaneity that a tankless cannot. Electric runs out here: no single residential electric tank recovers fast enough for a full-house morning of six.