Water Heater Dimensions

Dimensions matter twice: once when the new unit has to go through a doorway and into the alcove, and again when it has to leave enough clear space above and around it for the flue, the shutoff and the anode rod. The second one is where most jobs go wrong, because the cylinder fits and the install does not.

Published dimensions by capacity

Two patterns fall out of that table. Going up in capacity within one family usually costs you height rather than width. Going from tall to short at the same capacity costs you width instead — the Rheem 40-gallon short is nine inches lower and two inches fatter than the tall version of the same heater.

Quick picks

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Ranked picks with what each one is best for, our score and a link to check the current price on Amazon.

#	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	Rheem Performance 40 gal gasThe honest small-house gas tank: 36,000 BTU/h, around a 65-gallon first-hour delivery, and a recovery rate of about 36 gallons per hour — which is why a 40-gallon gas tank serves a family that would need a 50-gallon electric.	Smaller gas households	Check price on Amazon No live price feed on this site, so we show none. #ad
3	Rheem Performance Platinum 50 gal electricA plain, well-warranted 50-gallon electric tank: a 63 gallon-per-hour first-hour rating, 21 gallons per hour of recovery at a 90°F rise, and a 0.93 UEF.	Straight electric replacement	Check price on Amazon No live price feed on this site, so we show none. #ad

Tanks whose dimensions are published

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.

Published specifications for the A. O. Smith Signature 100, 50 gal gas

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.

Check price on Amazon

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 — Smaller gas households

Rheem Performance 40 gal gas

The honest small-house gas tank: 36,000 BTU/h, around a 65-gallon first-hour delivery, and a recovery rate of about 36 gallons per hour — which is why a 40-gallon gas tank serves a family that would need a 50-gallon electric.

Published specifications for the Rheem Performance 40 gal gas

Capacity	40 gallons
Input	36,000 BTU/h
First-hour delivery	65 gallons (Rheem PROG40-36N data); 68 gallons on the Performance retail model
Recovery	36.4 gallons per hour
Energy factor	0.62 (0.58 UEF on the retail Performance model)

What is good

• +Gas recovery means a 40-gallon tank behaves like a much larger electric one
• +Cheapest route to a working hot water supply for one or two bathrooms
• +Short and tall variants both exist, so it fits awkward spaces
• +Parts on the shelf at every supply house in the country

What is not

• −Published figures vary between the professional and retail versions of the same nominal unit — read the EnergyGuide label on the box you are buying
• −0.58 to 0.62 energy factor is the low end of current gas tanks
• −40 gallons is genuinely tight above three people

Skip it if: Skip it for a household of four or more with two bathrooms. The first-hour rating is adequate for one bathroom running at a time, and the complaint that follows a too-small tank is always the same: the last shower is cold.

Check price on Amazon

No live price feed on this site, so we show none. #ad

Specifications above from Young Supply listing, Rheem PROG40-36N; Rheem Performance 40 gal retail listing. We have not tested this unit ourselves.

Pick 3 — Straight electric replacement

Rheem Performance Platinum 50 gal electric

A plain, well-warranted 50-gallon electric tank: a 63 gallon-per-hour first-hour rating, 21 gallons per hour of recovery at a 90°F rise, and a 0.93 UEF.

Published specifications for the Rheem Performance Platinum 50 gal electric

Capacity	50 gallons
First-hour rating	63 gallons per hour
Recovery	21 gallons per hour at a 90°F rise
Efficiency	0.93 UEF
Voltage	240 V

What is good

• +Publishes recovery at a stated temperature rise, which most retail listings do not
• +0.93 UEF is at the top of what a resistance tank can do
• +Drop-in replacement dimensions for the previous generation
• +Available in short and tall variants

What is not

• −21 gallons per hour of recovery is a third of what a gas tank does
• −No leak detection on this model
• −Resistance heating is the most expensive way to make hot water in most of the country

Skip it if: Skip it if you have 7 feet of headroom and an unconditioned space to put it in. A heat pump model in that spot uses roughly a third of the electricity for the same hot water, and the payback is measured in a few years, not decades.

Check price on Amazon

No live price feed on this site, so we show none. #ad

Specifications above from Home Depot specification sheet, Rheem Performance Platinum electric (PDF). We have not tested this unit ourselves.

Tall, short and lowboy

• Tall is the default: roughly 57 to 62 inches for 40 and 50 gallons, and the narrowest diameter in the family.
• Short, sometimes sold as low-boy, holds the same water in a wider, lower cylinder — the trade is usually about two inches of extra diameter for nine or ten inches of height.
• Lowboy proper goes further still and is made for crawl spaces and under-counter installs. Expect a noticeably larger diameter again.
• Heat pump models are the tall exception. The compressor sits on top, so plan on around seven feet of clear height rather than five. Heat pump water heaters in a garage or basement covers the rest of the clearance picture.

The clearances nobody measures first

1. Above the tank. A gas unit needs room for the draft hood and the first length of flue; an electric unit needs room to pull the anode rod, which is roughly the height of the tank again unless you use a flexible rod.
2. In front. Enough to get a wrench on the cold inlet and the T&P discharge, and to get the old unit out without laying it down in a doorway.
3. Underneath. A drain pan adds its own depth. Camco's aluminium pans are 2-1/4 inches deep, which raises the connections by that much.
4. Around a gas unit. Combustion air is not a clearance you can measure with a tape; it is a volume requirement for the room. Water heater venting sets out which category you are in.
5. The route in. Measure the doorway, the stair turn and the hatch, not just the alcove.

When the tank will not fit

If the alcove was built for a 40 and you want a 50, you have four options before you start cutting drywall. Take the short version of the larger capacity. Stay at 40 gallons and move up in burner size instead — on gas that buys you more hot water than ten gallons of storage does, as 40 vs 50 gallon water heater sets out. Go tankless, which takes the problem off the floor entirely: the Rheem Prestige RTGH-95DVLN is 18-1/2 in W x 9-3/4 in D x 27-1/2 in H on a wall. Or serve the far fixture separately with a mini tank — the Eemax EMT6 is 18 in H x 15-3/4 in W x 15-1/2 in D inside a cabinet.

Footprints outside the tank category

Once you know the footprint, the sizing question is the one that actually decides what to buy: what size water heater do I need works through household size, and first-hour rating explained covers the number that matters more than capacity.