Best 40 Gallon Water Heaters
The right size for a smaller household, and a 15-gallon gap between fuels at the same badge number.
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A 40-gallon tank suits two to three people on gas and one to two on electric. The Rheem Performance 40 gallon gas unit delivers around 65 gallons in the first hour from 36,000 BTU/h with a recovery of 36.4 gallons an hour — which is what makes a 40-gallon gas tank behave like a much larger electric one.
Forty gallons is the smallest size we would put in a whole house, and it is genuinely the right choice for a lot of homes: a couple, a one-bathroom house, an apartment, an accessory dwelling. It is also frequently the largest tank that physically fits a closet install, where height clearance rather than floor space is the constraint.
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 |
The picks in full
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.
40 gallons, two very different appliances
| Fuel | Input | First-hour rating | Recovery |
|---|---|---|---|
| Natural gas | 36,000 BTU/h | 65 gal (Rheem PROG40-36N); 68 gal on the retail Performance model | 36.4 gal/hr |
| Electric resistance | 4,500 W x 2 | About 50 gal | 21 gal/hr at a 90°F rise |
Fifteen gallons of difference at the same badge number. In practice that is the difference between two comfortable showers and three, which is the difference between a 40-gallon tank working for a three-person household and not.
Our electric recommendation is a 50
You will notice the second pick on this page is a 50-gallon unit. That is deliberate. For one or two people a 40-gallon electric tank is fine, but the price difference to a 50 is small, the footprint difference is a few inches, and the capacity difference is the whole of your margin for a guest, a long bath, or a third person moving in.
If a 40-gallon electric tank is what fits, buy one — plenty of good ones exist. If a 50 fits, buy the 50. 50 gallon water heaters.
Who a 40 gallon tank suits
| Household | Gas 40 gal | Electric 40 gal |
|---|---|---|
| 1 person | Generous | Comfortable |
| 2 people | Comfortable | Adequate |
| 2 people, soaking tub | Adequate | Too small |
| 3 people, staggered | Adequate | Too small |
| 3 people, overlapping | Tight | Too small |
| 4+ | Too small | Too small |
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.
The install envelope
Forty-gallon tanks are commonly 18 to 20 inches in diameter where a 50 is 22. Three things that follow:
- A 20-inch drain pan fits a 40-gallon tank; a 50-gallon tank needs 22. Drain pan sizing.
- Short and tall variants of the same capacity exist. In a crawlspace or under a stair, the short version is the one that fits.
- Height clearance above the unit matters more than people expect: the flue connection on gas, and the cold inlet tee plus an expansion tank on anything. The Amtrol ST-12 expansion tank alone is 15 inches tall.
How we chose
Published first-hour rating and recovery at a stated rise, then warranty, then availability. We have not tested these units. How we pick.