What size water heater for a 3-bedroom house?
Size the house, not the current tenants: a 3-bedroom holds 4 people by the usual planning count (bedrooms plus one), and a full-house morning there runs about 86 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 |
The spread between gas and electric is recovery: a gas burner puts back about 43 gallons an hour while an element manages 20, so gas covers a 3-bedroom's full-house morning with a 75-gallon tank while electric needs more than one tank can hold to do the same job.
Three bedrooms, two baths, and one tank at the wrong end of the house
Three bedrooms is the most common layout in the American housing stock, which is why a 40-gallon tank is the most common thing standing in the basement of one. That default was picked by a builder pricing a house, not by anyone counting a Saturday morning, and the gap shows in the table above: a 40-gallon gas tank rates about 71 gallons in its first hour against the 86 a full three-bedroom house can ask for.
The layout matters as much as the count. The standard three-bed, two-bath plan puts the second bathroom at the far end of the house from the utility closet, and two showers running together is 5 GPM leaving the tank at once. That is a stored-water problem rather than a recovery problem: a 50-gallon tank holds about 35 usable gallons, and a simultaneous pair empties it in seven minutes. The first hour rating is describing an hour you are not having.
The distance costs you separately, and no tank fixes it. Fifty feet of three-quarter-inch copper holds about a gallon and a quarter of water that went cold overnight, and that gallon comes out of the far shower head before anything the heater did last night arrives. The fixes are a recirculation loop on a timer, a small point-of-use heater under the far sink, or patience.
If you are sizing to sell rather than to live, size to the bedrooms. A home inspector writes capacity up against the house and not against whoever happens to be standing in it, and a 40-gallon tank in a three-bedroom lands on the report as undersized even when the couple living there has never once run out.
Questions people ask
What size water heater comes standard in a 3-bedroom house?
Builders typically install a 40 or 50-gallon tank in a 3-bedroom house because it is the cheap default, not because anyone ran the numbers. At full occupancy (4 people) that default holds on gas, struggles on electric during a full-house morning.
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 3-bedroom house can hold 4 or more for most of that. Sizing to a couple in a 3-bedroom house saves maybe $100 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.