The 40-gallon and 50-gallon tanks are the two most common residential water heater sizes in the US. They look almost identical on a spec sheet, and they often share the same burner or elements. The right choice depends on how many people use hot water at the same time, whether the heater is gas or electric, and whether the bigger tank will fit where the old one sits.
The short answer
- Choose 40 gallons for one to three people, one or two bathrooms, and a gas heater, or when space is tight.
- Choose 50 gallons for three to five people, back-to-back morning showers, a large tub, or an electric heater serving three or more people.
If you are replacing a tank that has always kept up, replacing it with the same size is usually the safe choice. If you have been running out of hot water, moving from 40 to 50 gallons is one of the simplest fixes.
How the two sizes compare
| 40 gallon | 50 gallon | |
|---|---|---|
| Typical household | 1–3 people | 3–5 people |
| Weight of the water alone | About 334 lb | About 417 lb |
| Physical size | Smaller footprint or shorter height | Wider or taller; measure first |
| Standby heat loss | Lower | Slightly higher (more stored water) |
| First-hour rating | Lower | Higher with the same burner or elements |
| Purchase price | Lower | Usually somewhat higher |
Water weighs about 8.34 pounds per gallon, which is where the weights above come from. Add the weight of the tank itself, and a full 50-gallon heater is a heavy load for the floor, the stand and the person carrying it down the stairs.
Gas vs electric changes the math
Recovery rate is how quickly a heater reheats water after you use it. Gas burners recover much faster than electric elements, so the fuel type matters as much as the tank size.
Gas
Residential gas tanks with inputs around 36,000–40,000 BTU/h reheat roughly 35–40 gallons per hour at a 90°F rise. Because of that fast recovery, a 40-gallon gas tank often serves a family of three or four well. Higher-input models recover even faster. For example, Rheem's PROP-G40-50U 40 gallon has a 50,000 BTU/h input.
Electric
A standard 4,500-watt element reheats only about 20 gallons per hour at a 90°F rise. With slower recovery, the stored volume does more of the work. That is why many electric homes with three or more people choose 50 gallons. One example is the Rheem PROE50-T2-RH95.
Five questions to decide
1. How many showers run back to back?
A shower uses about 10 gallons of hot water on average. Count the showers in your busiest hour, add the dishwasher or laundry if they run at the same time, and compare that total with each model's first-hour rating on the EnergyGuide label.
2. Do you have a large tub?
Soaking tubs can hold far more hot water than a shower uses. If you fill one regularly, the 50-gallon tank is the safer choice.
3. Will the 50-gallon tank fit?
Measure the height, diameter and doorway widths, plus the clearances the manual requires. A 50-gallon tank is usually either taller or wider than a 40. Many electric models come in short, medium and tall versions, so you can often fit a 50 into a space that once held a 40.
4. Does the gas line and vent match?
For gas, keep the same fuel (natural gas or propane) and vent type: atmospheric, powered damper, power vent or direct vent. A higher-input heater may need a larger gas line. Moving to a different vent type adds cost.
5. Are you planning to add people or bathrooms?
A water heater usually stays in service for many years. If a growing family or a basement bathroom is likely, size for that now.
When neither size fits
- More than 50 gallons: 75-gallon gas tanks and larger electric tanks exist. Under federal efficiency standards in effect since 2015, residential tanks above 55 gallons generally use condensing (gas) or heat pump (electric) technology, which affects price and venting.
- Endless hot water: a tankless water heater is sized by flow rate rather than gallons and does not run out the same way.
- High efficiency electric: a heat pump water heater uses far less electricity than a standard electric tank, but it needs space and airflow around it.
Shop by size
Browse every 40-gallon Rheem we carry, gas and electric, in our Rheem 40 gallon water heaters collection. The 50-gallon models are together in Rheem 50 gallon water heaters.
Safety note: Water heater replacement involves gas piping, venting or a 240V circuit, plus a T&P relief valve that must be piped correctly. Have a licensed plumber, gas fitter or electrician do the installation, and follow local code for expansion tanks, drain pans and seismic straps.
Frequently asked questions
Is a 40 gallon water heater enough for a family of four?
Often yes with gas, because gas recovers quickly. With electric, a family of four is usually better served by 50 gallons. Check the first-hour rating against your busiest hour.
Does a 50 gallon water heater cost more to run?
Slightly, because more stored water means a little more standby heat loss. The difference is small compared with the hot water you actually use. Compare UEF ratings to see the real gap between two models.
Can I replace a 40 gallon with a 50 gallon?
Usually, if the larger tank fits the space and the gas line, venting or electrical circuit matches. Check the manufacturer's clearances and your local code before buying.
How long does a 50 gallon tank take to reheat?
A typical 40,000 BTU/h gas model reheats a full tank in roughly an hour or a little more. A 4,500-watt electric model takes much longer, often a few hours. The exact time depends on the incoming water temperature.