Short answer
Usually for one or two people, a small home or apartment, or a tight space. Rheem recommends 30 to 40 gallons for one to two people. Check the first-hour rating, not just the gallons: it is the hot water the tank delivers in your busiest hour. HomeGuide puts a 30-gallon tank at $500 to $1,900 installed.
Key facts
- Rheem's sizing guide recommends a 30 to 40 gallon tank for households of 1 to 2 people.[1]
- HomeGuide's January 2026 range for a 30-gallon tank is $300 to $900 for the unit and $500 to $1,900 installed.[2]
- DOE's Building America guide notes that 58% of U.S. households have one or two people, and estimates average use at about 17 gallons per person per day.[3]
Who a 30-gallon tank fits
A 30-gallon tank is the small end of the standard range. It usually fits:
- One or two people. Rheem recommends 30 to 40 gallons for households of 1 to 2 people[1]. HomeGuide's sizing chart lists 23 to 30 gallons for the same household size[2].
- Small homes, condos and apartments with one bathroom.
- Tight spaces, where a taller or wider 40 or 50 gallon tank will not fit.
- Manufactured homes, where 30-gallon models certified for that use are common (see below).
It is a good match for more households than people expect. DOE's Building America guide notes that 58% of U.S. households have one or two people, and that average use runs about 17 gallons per person per day, or about 50.6 gallons for a typical single-family home[3]. DOE rates hot water loads as low (about 20 gallons per day), moderate (45), above average (65) or high (110)[3].
Size by first-hour rating, not tank gallons
The tank size on the box is only part of the story. The number that predicts whether you run out is the first-hour rating (FHR): the most hot water, in gallons, the heater can supply in an hour that starts with a fully heated tank. ENERGY STAR notes the FHR is measured at a 125 F outlet temperature in the federal test[8]. Rheem describes it as how many gallons the unit can deliver during your busiest hour[1].
FHR depends on tank volume plus how fast the burner or elements reheat. That is why two 30-gallon heaters can perform very differently. One example: Rheem's 30-gallon Professional Classic direct vent gas model for manufactured housing lists an FHR of 49 gallons and a recovery of 30.3 gallons per hour at a 90 F rise[4].
How to use it: add up your household's busiest hour (for example, two showers back to back plus a dishwasher run) and pick a heater whose FHR meets or beats it. Our sizing guide walks through the math.
Gas vs electric at 30 gallons
| Gas 30-gallon | Electric 30-gallon | |
|---|---|---|
| Recovery | Faster: burner reheats quickly | Slower: elements reheat more slowly |
| What that means | Higher FHR for the same tank | May need a bigger tank to match a gas FHR |
| Install needs | Gas line, venting, combustion air | 240-volt circuit |
| 2029 DOE rule | Moderate efficiency increase | Depends on class and draw pattern (below) |
HomeGuide notes that electric water heaters have a slower recovery rate and need a larger tank than gas models for the same household[2]. If your home is electric and you are on the edge between 30 and 40 gallons, the larger tank is the safer pick.
What a 30-gallon tank costs
HomeGuide's January 2026 national ranges[2]:
| Tank size | Unit only | Installed |
|---|---|---|
| 30 gallon | $300 to $900 | $500 to $1,900 |
| 40 gallon | $400 to $2,000 | $600 to $3,000 |
| 50 gallon | $500 to $2,100 | $700 to $3,100 |
The gap between 30 and 40 gallons is often small once labor is included. Venting changes, a new expansion tank, code upgrades or a hard-to-reach space move the price more than tank size does. These ranges are national and not quotes.
Manufactured and mobile homes need a listed model
Standard residential gas heaters are not built for manufactured homes. A State residential gas manual says on its cover: "Not for use in manufactured (mobile) homes"[7]. Models for that use are certified for it. Rheem's 30-gallon Professional Classic direct vent unit, for example, is "certified for manufactured (HUD) and modular construction"[4]. If you live in a manufactured home, make sure the replacement carries that certification.
The 2029 DOE rule and 30-gallon electric tanks
DOE's efficiency standard for water heaters made on or after May 6, 2029 raises most electric tanks of 20 to 55 gallons to a heat pump level (a uniform energy factor of 2.30)[5]. The same table keeps a separate class, "small electric storage water heaters," for 20 to 35 gallons. That class has standards only for the very small and low draw patterns, and they stay close to today's resistance-heater level[5].
The draw pattern comes from the FHR. A heater with an FHR of 18 to under 51 gallons is tested on the low-usage pattern, and 51 to under 75 gallons on the medium pattern[6]. So some 30-gallon electric tanks may stay available as standard resistance units after 2029, while others would need to meet the heat pump level. Whether a given model qualifies depends on DOE's class definitions and the maker's certification. Gas tanks of 20 to 55 gallons get a moderate increase, not a ban[5]. See DOE water heater rules.
Checks before you buy
- Read the FHR on the yellow EnergyGuide label or the spec sheet of both your old and new heater.
- Measure height, width and door or closet clearances. Small spaces are the main reason people choose 30 gallons.
- Confirm the fuel, venting type and, for gas, that the replacement is listed for your home type.
- Compare warranty length. The same tank size often comes in several warranty tiers at different prices.
When to call a pro
- Any replacement: water heater swaps generally need a permit, and gas or 240-volt work is licensed.
- Switching fuel, changing vent type, or moving the heater to a new spot.
- Replacing a heater in a manufactured home, where the model must be certified for that use.
- Running out of hot water often on a 30-gallon tank: a pro can confirm whether size, sediment or a failed part is the cause.
More questions
Can I replace a 40-gallon tank with a 30-gallon one?
You can if your household's peak-hour use fits the smaller tank's first-hour rating. Compare the FHR on both labels. Gas tanks recover faster than electric ones, so a gas 30 may come closer to a 40 than you expect. Check the actual numbers.
Is a 30-gallon tank cheaper to run than a 50?
A smaller tank has less surface to lose heat through, so it generally loses less heat while it sits. Your hot water use matters more than tank size. Running out and reheating is not wasteful in itself, but an undersized tank that leaves you without hot water is a poor trade.
Sources
- What size gas water heater do I need for my home? (Sep 2, 2026), Rheem Manufacturing. Accessed 2026-10-06.
- How much does water heater installation or replacement cost? (Jan 2, 2026), HomeGuide. Accessed 2026-10-06.
- Strategy Guideline: Proper Water Heater Selection (rev. Apr 2015), U.S. Department of Energy, Building America. Accessed 2026-10-06.
- Professional Classic Direct Vent for Manufactured Housing (PROG30-30N RH63 MH DV), Rheem Manufacturing. Accessed 2026-10-06.
- 10 CFR 430.32(d), energy conservation standards for water heaters, Legal Information Institute, Cornell Law School. Accessed 2026-10-06.
- 10 CFR Part 430, Subpart B, Appendix E: Uniform test method for water heaters, Legal Information Institute, Cornell Law School. Accessed 2026-10-06.
- Instruction Manual for Residential Gas Water Heaters (184115-000), State Water Heaters. Accessed 2026-10-06.
- ENERGY STAR water heater key product criteria (glossary), ENERGY STAR (U.S. EPA). Accessed 2026-10-06.
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