Best Size Water Heater for a Family of 5
Five people is where first-hour rating stops being a technicality and starts deciding whether the last shower is warm.
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A family of five needs 80 gallons or more in the peak hour. On gas that is still a 50-gallon tank, because a good one delivers 91 gallons in the first hour. On electric resistance it is an 80-gallon tank. On a heat pump, 66 gallons with a first-hour rating in the low 80s.
This is the page where the gas-versus-electric gap becomes concrete. A 50-gallon gas tank and an 80-gallon electric tank can serve the same five-person household. They are different physical sizes, different installs, and different prices, and the reason they are equivalent has nothing to do with volume.
Why a 50 gallon gas unit beats an 80 gallon electric one
Recovery rate. A 50,000 BTU gas burner reheats the tank while you are still drawing from it — that is how a 50-gallon tank ends up with a 91-gallon first-hour rating. An electric tank with two 4,500 W elements recovers about 21 gallons an hour at a 90°F rise, so its first-hour rating is barely more than its volume: an 80-gallon electric tank is rated at 78 gallons in the first hour.
| Unit | Capacity | First-hour rating | What it means |
|---|---|---|---|
| A. O. Smith Signature 100 gas, 50,000 BTU | 50 gal | 91 gal | Comfortable for five, with headroom |
| A. O. Smith Voltex MAX heat pump | 66 gal | 83 gal | Comfortable for five at a quarter of the running cost |
| A. O. Smith ProLine XE heat pump | 66 gal | 79 gal | Adequate for five, cheaper to buy than the MAX |
| Rheem Professional Classic electric | 80 gal | 78 gal | Adequate for five; note the rating is BELOW the tank volume |
| Rheem Gladiator electric | 50 gal | 63 gal | Not enough for five. This is the mistake people make |
Where 80 gallons comes from
Four showers plus a sink plus an appliance, inside one hour. At 14 hot gallons per 10-minute shower that is 56 gallons before anything else runs. Add a bath, a dishwasher or a laundry load on hot and you are past 80 quickly. Five-person households also tend to have two bathrooms genuinely in simultaneous use, which is the variable that matters most.
Quick picks
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| # | Product | Best for | Price |
|---|---|---|---|
| 1 |  A. O. Smith Signature 100, 50 gal gasThe straightforward 50-gallon gas replacement, and the reason to pay attention to the burner size: the 50,000 BTU version is rated at a 91-gallon first-hour rating against 77 gallons for the 40,000 BTU one. | Most gas tank replacements | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 2 |  A. O. Smith Voltex MAX, 66 galAn 83-gallon first-hour rating at a 3.84 UEF — the heat pump water heater for a household that runs several showers back to back and still wants the running cost of a heat pump. | Largest first-hour rating | Check price on Amazon No live price feed on this site, so we show none. #ad |
| 3 |  Rheem Professional Classic 80 gal electricThe big resistance tank: 80 gallons of storage and a 78-gallon first-hour rating, which is how you cover a six-person household when gas is not an option and a heat pump will not fit. | Large households on electric only | Check price on Amazon No live price feed on this site, so we show none. #ad |
What we would buy for five people
Pick 1 — Most gas tank replacements
A. O. Smith Signature 100, 50 gal gas
The straightforward 50-gallon gas replacement, and the reason to pay attention to the burner size: the 50,000 BTU version is rated at a 91-gallon first-hour rating against 77 gallons for the 40,000 BTU one.
| Capacity | 50 gallons |
|---|---|
| First-hour rating | 91 gallons (50,000 BTU model); 77 gallons (40,000 BTU model) |
| Burner | 50,000 BTU/h ultra-low NOx, or 40,000 BTU/h |
| Dimensions | 61 in H x 22 in dia (50,000 BTU); 60-3/4 in H x 22 in dia (40,000 BTU) |
| Warranty | 6-year tank and parts with 1-year labor (50,000 BTU); 9-year tank and parts with 2-year labor (40,000 BTU) |
What is good
- A 91-gallon first-hour rating from a 50-gallon tank covers back-to-back showers that empty an electric tank of the same size
- Widely stocked at Lowe's, so same-day replacement is realistic when the old one fails
- Ultra-low NOx burner meets the stricter air-district rules in California and Texas
- 22-inch diameter fits most existing alcoves without re-plumbing
What is not
- The longer 9-year warranty is on the smaller burner, so warranty and recovery pull in opposite directions
- Atmospheric venting needs a working chimney or B-vent
- Standing pilot and flue losses mean it idles energy away all day
Skip it if: Skip it if your water heater sits in a sealed closet or a space with combustion air problems. An atmospheric gas tank needs real combustion air and a real flue — the power-vent or direct-vent models exist for exactly that case.
No live price feed on this site, so we show none. #ad
Specifications above from Lowe's listing, Signature 100 50-gal 50,000 BTU; Lowe's listing, Signature 100 50-gal 40,000 BTU 9-year. We have not tested this unit ourselves.
Pick 2 — Largest first-hour rating
A. O. Smith Voltex MAX, 66 gal
An 83-gallon first-hour rating at a 3.84 UEF — the heat pump water heater for a household that runs several showers back to back and still wants the running cost of a heat pump.
| Capacity | 66 gallons |
|---|---|
| First-hour rating | 83 gallons |
| Efficiency | 3.84 UEF |
| Certification | ENERGY STAR certified |
What is good
- 83 gallons in the first hour beats an 80-gallon resistance tank
- 3.84 UEF is still roughly four times a resistance tank
- 66 gallons of storage plus fast recovery is the combination big households actually need
- ENERGY STAR certified for rebate eligibility
What is not
- Lower UEF than the Voltex AL at the same capacity — you are trading some efficiency for delivery
- Large footprint
- Wholesale distribution
Skip it if: Skip it if two people live in the house. You would be buying 66 gallons and an 83-gallon first-hour rating to serve a demand a 50-gallon unit covers, and paying standby losses on the difference every day for a decade.
No live price feed on this site, so we show none. #ad
Specifications above from First Supply listing, A. O. Smith HPTA-66 Voltex MAX. We have not tested this unit ourselves.
Pick 3 — Large households on electric only
Rheem Professional Classic 80 gal electric
The big resistance tank: 80 gallons of storage and a 78-gallon first-hour rating, which is how you cover a six-person household when gas is not an option and a heat pump will not fit.
| Capacity | 80 gallons |
|---|---|
| First-hour rating | 78 gallons |
| Elements | 4.5 kW, 2 elements |
| Voltage | 240 V |
| Efficiency | 0.93 UEF |
What is good
- Storage volume does the work that electric recovery cannot
- 78 gallons in the first hour genuinely covers four back-to-back showers
- Simple: two elements, two thermostats, parts available everywhere
- Nothing to service annually
What is not
- Physically large — it will not fit where a 50-gallon tank fit
- 80 gallons of standby loss, every hour of every day
- First-hour rating is lower than its own capacity, which tells you how slow the recovery is
Skip it if: Skip it if the space is tall enough for an 80-gallon heat pump model. You are choosing the version of the same tank that costs roughly three times as much to run, for no gain other than a lower sticker price.
No live price feed on this site, so we show none. #ad
Specifications above from Ferguson listing, Rheem Professional Classic 80 gal electric. We have not tested this unit ourselves.
The tankless option at this size
Five people is where gas tankless starts to look genuinely attractive, because the constraint stops being storage and becomes simultaneous flow — which is what tankless is good at. A 199,000 BTU condensing unit delivers 5.5 GPM at a 70°F rise, enough for two showers plus a sink in a cold-inlet climate, and it never runs out regardless of how many showers happen in sequence.
The honest caveat: the gas line has to be able to feed nearly 200,000 BTU/h, and upsizing it is frequently the biggest single cost in the conversion. Tankless vs tank has the cost-of-ownership comparison, and best tankless water heaters has the units.
If you cannot fit a bigger tank
- Raise the tank temperature and fit a mixing valve. Storing at 140°F and mixing down to 120°F at the outlet gives you more usable hot water from the same volume, and it is the standard trick for a space-constrained install.
- Fit low-flow shower heads. 2.5 GPM to 1.75 GPM is roughly a 30% cut in the biggest line item in your peak hour.
- Stagger the schedule. Unromantic, free, and genuinely effective — a 50-gallon electric tank serves five people fine if the draws are 40 minutes apart.
- Add a point-of-use heater at the far fixture. Removes the wait and the water wasted waiting. See point-of-use water heaters.
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.