Comparison
40 vs 50 gallon water heater
Tank gallons are the wrong comparison. The spec sheets we checked put 40-gallon gas tanks at 64–84 gallons of First Hour Rating and 50-gallon electric tanks at 60–63. Pick the tank whose FHR covers your busiest hour, whatever its size.
Updated
Real First Hour Ratings from spec sheets
These are current residential models from Bradford White, Rheem and A. O. Smith, with the First Hour Rating printed on each manufacturer’s spec sheet. They are examples, not recommendations; ratings change as models are updated.
| Type | Model | Input | FHR |
|---|---|---|---|
| 40-gallon gas | Bradford White RG240T6N | 40,000 BTU/hr | 75 gal |
| Bradford White RG140T6N | 34,000 BTU/hr | 64 gal | |
| Rheem PRO+G40-40N RH62 | 40,000 BTU/hr | 84 gal | |
| A. O. Smith GCR-40 | 40,000 BTU/hr | 80 gal | |
| 50-gallon gas | Bradford White RG250T6N | 40,000 BTU/hr | 81 gal |
| Rheem PRO+G50-40N RH62 | 40,000 BTU/hr | 76 gal | |
| A. O. Smith GCR-50 | 40,000 BTU/hr | 84 gal | |
| 40-gallon electric | Bradford White RE340T6 | Elements | 53 gal |
| Rheem PROE40 T2 RH95 | Elements | 55 gal | |
| A. O. Smith ENT-40 | Elements | 53 gal | |
| 50-gallon electric | Bradford White RE350S6 | Elements | 60 gal |
| Rheem PROE50 T2 RH95 | Elements | 63 gal | |
| A. O. Smith ENT-50 | Elements | 62 gal | |
| 50-gallon heat pump | Rheem PROPH50 T2 RH400-SO | Heat pump | 67 gal |
| A. O. Smith HPTS-50 | Heat pump | 65 gal | |
| Bradford White RE2HP5010 | Heat pump | 65 gal |
Three things stand out:
- Every 40-gallon gas model rates higher than every 50-gallon electric model in this set: 64–84 gallons against 60–63.
- A bigger tank isn’t always more. Rheem’s 40-gallon PRO+G40-40N RH62 rates 84 gallons; its 50-gallon sibling on the same sheet rates 76. 50-gallon gas models overall: 76–84.
- Going from 40 to 50 gallons electric adds roughly 5 to 10 gallons of FHR (53–55 vs. 60–63), not 10.
Which busiest hours each covers
Here are the worked household examples from our household guide, with the FHR each needs. A tank covers a household when its FHR is at least that number.
| Household | Busiest hour | FHR at 50°F | FHR at 40°F | Covered by |
|---|---|---|---|---|
| 2 people | 2 standard showers, 2 bathroom faucets, 1 kitchen faucet | 38 | 39 | any 40-gal electric, any 40-gal gas listed |
| 3 people | 3 standard showers, 2 bathroom faucets, 1 kitchen faucet, a dishwasher load | 59 | 61 | any 50-gal electric, any 40-gal gas listed |
| 4 people | 4 standard showers, 3 bathroom faucets, 1 kitchen faucet, a dishwasher load | 76 | 78 | some 40-gal gas |
| 5 people | 4 standard showers, 3 bathroom faucets, 1 kitchen faucet, a bath, a dishwasher load | 103 | 106 | Larger or faster-recovering tank |
| 6 people | 5 standard showers, 4 bathroom faucets, 1 kitchen faucet, a bath, a dishwasher load, a hot/warm wash | 130 | 133 | Larger or faster-recovering tank |
FHR is rated with 58°F incoming water. In colder water a tank delivers less than its rating, so leave a margin, especially if you’re near the line.
How to decide
- Work out your peak-hour demand with the calculator.
- Look up the First Hour Rating of the specific models you’re considering on their EnergyGuide labels or spec sheets.
- Choose one whose FHR is at least your demand, with some margin if your incoming water is colder than 58°F.
- If no tank that fits your space and fuel covers it, look at a higher-input tank, a larger heat pump model, or tankless.
40 vs 50 gallon questions
Is a 40 or 50 gallon water heater better for a family of 4?
Compare First Hour Rating, not gallons. In our worked example a family of four needs about 76 gallons of FHR at 50°F incoming water. The 40-gallon gas models we checked rate 64–84 gallons and the 50-gallon electric models 60–63, so the answer depends on the specific model and your busiest hour.
How much more hot water does a 50 gallon tank give than a 40?
Less than the 10 gallons you might expect, and sometimes none. On Rheem's own spec sheet, the 40-gallon PRO+G40-40N RH62 rates 84 gallons First Hour Rating and the 50-gallon PRO+G50-40N RH62 rates 76, with the same 40,000 BTU/hr burner.
Why do electric tanks have lower First Hour Ratings?
Recovery. A typical residential electric tank heats with one 4,500 watt element at a time, about 15,000 BTU/hr, while the gas models we checked use 34,000 to 40,000 BTU/hr burners. The gas tank reheats much more water during the test hour.
Should I replace a 40 gallon with a 50 gallon?
Only if your busiest hour needs a higher First Hour Rating than your current heater has. If you run out of hot water, first check for a failed element, sediment or a lowered setpoint, then compare your peak-hour demand with the FHR of the replacement you are considering.
Sources
Water Heater Sizing Calculator for iPhone
Take the calculator to the job site
The app runs the same sizing engine as this site, offline. Basic tank and tankless sizing is free. Lifetime Pro, a one-time $4.99 purchase, adds tank vs. tankless comparison, custom fixtures, saved jobs with notes and PDF reports you can send to a customer.
