40 Gallon Water Heater: How Many People?
The answer depends entirely on the fuel, and the gap between gas and electric at this size is wide.
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A 40-gallon water heater comfortably serves two to three people on gas and one to two on electric resistance. A 40-gallon gas tank is rated at roughly 65 to 68 gallons in the first hour; a 40-gallon electric tank is rated nearer 50. Fuel, not volume, is what decides it.
Forty gallons is the smallest size most houses should consider for a whole-home heater, and it is a perfectly good choice for the household it fits. The problem is that the same number means two quite different appliances depending on what heats it.
40 gallons on gas
A 36,000 BTU gas tank recovers around 36 gallons an hour, which is why Rheem publishes a first-hour delivery of about 65 gallons for its 40-gallon Performance unit. That covers two showers back to back plus a sink comfortably, and three showers if the third is short or 20 minutes later.
For a two-bathroom, three-person house on gas, a 40-gallon tank is a sensible and cheaper choice than a 50. The caveat is that published figures vary between the professional and retail versions of nominally the same unit — read the EnergyGuide label on the box you are actually buying.
40 gallons on electric
An electric tank with two 4,500 W elements recovers about 21 gallons an hour at a 90°F rise, so a 40-gallon electric tank's first-hour rating lands around 50 gallons. That is one generous shower and a sink, or two short showers. Two people, fine. Three, and the third person is taking a cool shower on busy mornings.
| Household | Gas 40 gal | Electric 40 gal |
|---|---|---|
| 1 person | Generous | Comfortable |
| 2 people | Comfortable | Adequate |
| 2 people with a soaking tub | Adequate | Too small |
| 3 people, staggered showers | Adequate | Too small |
| 3 people, overlapping showers | Tight | Too small |
| 4 or more | Too small | Too small |
Quick picks
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| # | Product | Best for | Price |
|---|---|---|---|
| 1 |  Rheem Performance 40 gal gasThe honest small-house gas tank: 36,000 BTU/h, around a 65-gallon first-hour delivery, and a recovery rate of about 36 gallons per hour — which is why a 40-gallon gas tank serves a family that would need a 50-gallon electric. | Smaller gas households | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 2 |  Rheem Gladiator 50 gal electricThe electric tank to put above a finished floor: integrated leak detection with an automatic shutoff valve that limits a leak to around 20 ounces, plus a 12-year tank and parts warranty. | Electric tanks in finished spaces | Check price on Amazon No live price feed on this site, so we show none. #ad |
What to buy at 40 gallons
Pick 1 — Smaller gas households
Rheem Performance 40 gal gas
The honest small-house gas tank: 36,000 BTU/h, around a 65-gallon first-hour delivery, and a recovery rate of about 36 gallons per hour — which is why a 40-gallon gas tank serves a family that would need a 50-gallon electric.
| Capacity | 40 gallons |
|---|---|
| Input | 36,000 BTU/h |
| First-hour delivery | 65 gallons (Rheem PROG40-36N data); 68 gallons on the Performance retail model |
| Recovery | 36.4 gallons per hour |
| Energy factor | 0.62 (0.58 UEF on the retail Performance model) |
What is good
- Gas recovery means a 40-gallon tank behaves like a much larger electric one
- Cheapest route to a working hot water supply for one or two bathrooms
- Short and tall variants both exist, so it fits awkward spaces
- Parts on the shelf at every supply house in the country
What is not
- Published figures vary between the professional and retail versions of the same nominal unit — read the EnergyGuide label on the box you are buying
- 0.58 to 0.62 energy factor is the low end of current gas tanks
- 40 gallons is genuinely tight above three people
Skip it if: Skip it for a household of four or more with two bathrooms. The first-hour rating is adequate for one bathroom running at a time, and the complaint that follows a too-small tank is always the same: the last shower is cold.
No live price feed on this site, so we show none. #ad
Specifications above from Young Supply listing, Rheem PROG40-36N; Rheem Performance 40 gal retail listing. We have not tested this unit ourselves.
Pick 2 — Electric tanks in finished spaces
Rheem Gladiator 50 gal electric
The electric tank to put above a finished floor: integrated leak detection with an automatic shutoff valve that limits a leak to around 20 ounces, plus a 12-year tank and parts warranty.
| Capacity | 50 gallons |
|---|---|
| Elements | 5,500 W double element, 240 V |
| First-hour rating | 63 gallons |
| Efficiency | 0.92 UEF |
| Leak protection | 360° LeakSense detection with factory-fitted automatic shutoff; leaks limited to no more than 20 oz |
| Warranty | 12-year tank and parts, 3-year labor |
What is good
- The auto-shutoff valve is the single most valuable feature on any tank installed over drywall
- 12-year tank and parts with 3-year labor is among the longest electric warranties sold at retail
- 5,500 W double element gives faster recovery than the usual 4,500 W pair
- Leak alerts arrive before the ceiling does
What is not
- A 63-gallon first-hour rating from 50 gallons is ordinary — electric recovery is slow, full stop
- Running cost is electric-rate running cost; a heat pump model costs far less to run
- The shutoff valve is one more serviceable part in the cold inlet
Skip it if: Skip it if the heater lives on a concrete slab next to a floor drain and you have the headroom for a heat pump model. You are paying for leak protection you can get from a 20-dollar pan, and giving up the running-cost saving a heat pump would deliver.
No live price feed on this site, so we show none. #ad
Specifications above from Home Depot listing, Rheem Gladiator XE50T12CS55U1. We have not tested this unit ourselves.
When to size up instead
- You have a soaking tub. A deep tub fill can take 60 to 80 gallons of mixed water. One fill empties a 40-gallon tank and most of its recovery.
- Your inlet water is cold. A northern winter inlet means a larger rise, which slows recovery on every fuel and eats into the first-hour rating.
- You are replacing electric with electric and the household has grown. This is the commonest case for sizing up, and it is usually a 50 or 65 gallon decision.
- You are switching to a heat pump. A 50-gallon heat pump unit is barely larger in footprint than a 40-gallon resistance tank and has a far better first-hour rating, so there is rarely a reason to buy a 40-gallon heat pump.
When 40 gallons is the right answer
A one or two-person household, a rental unit, an apartment, an accessory dwelling, or a second bathroom served by its own heater. Forty gallons is also the practical maximum in a lot of closet installs, where height clearance for the flue or the cold inlet and expansion tank is the real constraint rather than floor space.
What goes in with it
A water heater is a system, not a box. These are the parts that go in with it, and the ones people discover they need halfway through the job.
- Expansion tank
Required by code on a closed system, which is most homes with a pressure-reducing valve.
- Drain pan
Cheap insurance anywhere the tank sits above something you care about.
- Anode rod
The part that decides when the tank leaks. Replacing it is the highest-value hour of maintenance there is.