What size water heater for a 5-bedroom house?
Size the house, not the current tenants: a 5-bedroom holds 6 people by the usual planning count (bedrooms plus one), and a full-house morning there runs about 126 gallons of hot water. That takes a 75 gal gas tank, and no single electric tank covers it. A calmer household can step down the table below.
From full house to quiet couple, in gallons
Rows run from every bed filled and everyone showering in the same hour down to one shower. Each row carries one shave and one round of hand dishes (6 gallons of sink use). The full-house row is what this house can demand of the tank; where you actually live on the table is a judgment call the next owner may not share.
| 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 |
| 5 | 106 gal | 75 gal | none fits | 71 gal | 50 gal | 80 gal |
| 6 | 126 gal | 75 gal | none fits | 84 gal | 75 gal | none fits |
Past this size the electric column mostly reads "none fits," and that is real: 6 standard showers in an hour outruns any single residential electric tank. 5-bedroom houses with electric-only service end up at two tanks, an 80-gallon plus discipline, a heat pump unit sized up, or a tankless if the panel and gas line allow.
Five bedrooms is where a bigger tank stops being an option
A full five-bedroom house is 126 gallons in the busiest hour, and a 75-gallon gas tank rates about 133. That margin is under a third of one shower. This is the size where the answer stops being "buy the next tank up", because there is no next tank: 75 gallons is the top of the residential gas catalogue, 80 is the top of electric, and the electric column in the table above ran out three rows earlier.
Five-bedroom houses also tend to carry two bathing clusters that are nowhere near each other, often because one of them started life as a basement or an in-law suite. When that is true, a second heater near the second cluster beats the biggest single tank on every measure that matters, and it is usually what a plumber standing in the house will propose. Two 50-gallon gas units in series deliver close to the sum of their first hour ratings, which is more than the 75 manages, and they skip the flue work the 75 sometimes forces.
Watch the gas supply whichever way you go. Two 40,000 BTU tanks plus a furnace and a range on a single half-inch branch will outrun the pipe long before it outruns the meter, and the symptom is not a cold shower. It is a burner that will not stay lit when the furnace calls on the coldest night of the year. That sum belongs to whoever pulls the permit.
Questions people ask
What size water heater comes standard in a 5-bedroom house?
Builders typically install a 50-gallon tank in a 5-bedroom house because it is the cheap default, not because anyone ran the numbers. At full occupancy (6 people) that default is undersized for a full-house morning on either fuel.
Should I size for the bedrooms or for who lives here now?
Bedrooms, if the tank will outlive the current household. A tank runs 8 to 12 years; a 5-bedroom house can hold 6 or more for most of that. Sizing to a couple in a 5-bedroom house saves maybe $200 today and gets re-bought by the next full household.
Does a spare bathroom change the size?
Not for a tank. Tank sizing counts gallons in the busiest hour, and an extra bathroom does not shower anybody extra; it just lets two showers happen at once, which is a tankless-sizing (GPM) problem, not a gallons problem.