Rheem Performance 40-Gallon Short Gas Water Heater

The Rheem Performance 40-Gallon Short Gas Water Heater (XG40S06EC34U0) is the full-40-gallon short-form tank — the recovery and FHD of a standard 40G in a low-clearance form factor. Atmospheric venting, 6-year warranty, 34,000 BTU.

Headline specifications

• Model: XG40S06EC34U0
• Capacity: 40 gallons
• Fuel: Natural gas, atmospheric vent
• BTU input: 34,000 BTU/h
• First Hour Delivery: 67 GPH
• Recovery: 34 GPH at 90°F rise
• UEF: 0.60
• Warranty: 6-year
• Dimensions: 50" H × 22" diameter

Who this model is for

The 40G Short is the low-clearance alternative to the standard 60"-tall Performance Plus 40G. It preserves 40-gallon capacity while reducing height to 50" — enough clearance gain to fit basement rim-joist installs, manufactured-home closets, and finished basements with low ceilings.

For full-clearance installs, the standard 40G is the correct sizing — same warranty, slightly higher recovery (40 GPH vs 34 GPH), $30 less. For very low clearance (under 50"), drop to Performance 38G Short. For 18"-diameter constraint, see Performance 29G Compact.

Where it beats the alternatives

Vs Performance Plus 40G standard-height: short-form is 10" shorter for the same capacity. Trade is 5 GPH less recovery (34 vs 40) and slightly lower UEF (0.60 vs 0.63). Worth it only for low-clearance installs.

Vs Performance 38G Short: 40G Short adds 2 gallons of capacity for ~$30 more. If your install accommodates the slightly taller 50" form factor, choose 40G Short.

Vs all-electric short tank: gas operating cost is ~$300/year less for 2–3 person households at typical US natural gas rates. Gas wins where natural gas service is available.

Where it falls short

34,000 BTU recovery is slow for a 40G — full reheat after depletion takes ~70 minutes. Households with concentrated evening demand will notice.

67 GPH FHD trails standard 40G (75 GPH).

0.60 UEF is bottom of class. Operating cost ~$260–$320/year for 2–3 person households.

Atmospheric venting only.

The "short" form factor's flat-bottom geometry accumulates sediment faster than tall narrow tanks. Annual flushing matters more here.

Install considerations

50" height + 22" diameter. Verify floor-to-ceiling clearance includes ~6" above for connections. 1/2" gas line. Atmospheric flue inspection.

Install cost: $700–$1,300 like-for-like swap.

Maintenance

• Annual flush — important for short-form geometry
• Anode check year 3, replace year 5
• T&P valve test annually
• Burner inspection every 2 years

Bottom line

The Rheem Performance 40G Short Gas (XG40S06EC34U0) is the full-capacity low-clearance gas tank — 50" height with 40-gallon capacity. Right pick for basement rim-joist, manufactured-home, and low-ceiling installs needing 40G capacity. For full-clearance installs, choose the standard Performance Plus 40G. For tighter clearance, drop to Performance 38G Short.