40-gallon is the small standard residential size — appropriate for 1-2 person households or 2-3 person households with low simultaneous demand. Smaller than the volume 50-gallon class, it costs less, takes up less floor space, and recovers faster between uses.
When 40-gallon is right
- 1-2 person household
- Single bathroom homes with 2-3 occupants
- Apartments and condos
- Mobile homes (lowboy 38-gallon also viable)
- Like-for-like replacement of existing 40-gallon
When 40-gallon is too small
- 3-4 person household with 2 bathrooms
- Back-to-back showers
- Large soaking tub
- Simultaneous laundry + shower
For 3-4 person households, step up to 50-gallon. For 4-5 person, consider 66 or 75-gallon.
Top 40-gallon picks by category
Gas (40-gallon natural gas)
- Volume budget: Rheem Performance 40-gal ($649-849)
- Mid-tier: AO Smith Signature Select 40-gal ($749-949)
- Premium plumber-channel: Bradford White RG240T6N 40-gal ($849-999)
Electric (40-gallon electric)
- Volume budget: Rheem Performance 40-gal electric ($549-749)
- Lifetime composite: Marathon MR40 ($1,199-1,499)
- Lifetime stainless: Westinghouse WER040 ($1,149-1,449)
Install requirements (40-gallon)
- Footprint: typically 19-22" diameter, 50-60" tall
- Gas: standard B-vent chimney, ½" gas line adequate for 30-40k BTU
- Electric: 240V 30A dedicated circuit, 10/2 NM cable
- T&P relief and drain pan per code
First-hour delivery
- 40-gallon gas: ~70-72 GPH
- 40-gallon electric: ~54 GPH
- 40-gallon heat pump (HPWH): ~50 GPH
Typical cost installed
| Type | Installed cost |
|---|---|
| 40-gal gas tank, like-for-like swap | $1,000-1,700 |
| 40-gal electric tank, like-for-like swap | $900-1,500 |
| 40-gal HPWH electric (after IRA credit) | $1,000-1,700 net |
Bottom line
40-gallon is the small standard size. For 1-2 person households, this is the right capacity. Verify your simultaneous-demand profile — if back-to-back showers or simultaneous laundry are common, size up to 50-gallon instead.