Rheem RTGH-S84I
0.96 UEF DOE CCD · 2026-09-19Grade A: where this UEF sits among the 397 models in its class, lowest (G) to highest (A). A position, not an official label. How the grade is set
A gas tankless unit, high draw pattern (a larger household, or one where showers and laundry overlap).
If you are checking the Rheem RTGH-S84I, this gas tankless unit uses 176 therms of natural gas a year. That figure is for the high draw pattern, the standard daily hot-water usage DOE tests against. It sits 6 therms below the class median of 182 therms and ranks 12th lowest in energy use of 397 comparable models.
Energy use per year
176 therms a year
Computed by this site from the registry's UEF and the federal test's daily hot-water draw for this draw pattern. What it costs depends on the natural gas rate where you live.
That is below the median of 182 therms for the 397 models registered in the same heater type and draw pattern; it ranks 12 of 397, lowest energy first.
Solid line: this model (176 therms). Dashed line: the class median.
Min 173 therms Median 182 therms Max 209 therms
What it costs to run where you live
What the registry files
- UEF (Uniform Energy Factor) how much hot water you get for each unit of energy the heater uses
- 0.96 DOE CCD · 2026-09-19 Compared only with other models registered as a gas tankless unit at the high draw pattern.
- Draw Pattern the standard daily usage profile DOE tests the unit against
- High DOE CCD · 2026-09-19
- Maximum Gallons Per Minute how many gallons a minute it can heat while running continuously
- 4.6 gal/min DOE CCD · 2026-09-19
- On the market since (ENERGY STAR) the date the manufacturer told ENERGY STAR the model went on sale
- 2023-01-01 ENERGY STAR · 2026-09-19
- Connected / demand response (ENERGY STAR) whether the unit can take signals from your utility to shift when it heats, and by which standard (such as CTA-2045)
- No ENERGY STAR · 2026-09-19
What it costs to install
$2,405–$3,460 installed
Not a quote — a modeled range of what installers have charged for this class of unit; your price will vary with labor rates, access, and local code requirements.
Escalation indexes: equipment (BLS PPI) latest available: August 2026; labor (BLS ECI) latest available: April 2026 to June 2026.
NLR REMDB (BLS PPI/ECI escalated) · 2026-04-01Safety record
No CPSC recall names this model.
Checked against the CPSC recall database. CPSC does not publish a model-level match for this product category, so this list is curated by hand from the manufacturer's recall filings.
CPSC · 2026-09-24Does it fit your space?
Enter your own numbers below — this compares them to what ENERGY STAR publishes for this model, it does not tell you what to buy.
- Dimensions (ENERGY STAR)
- the unit's filed height, width, depth or tank diameter, in inches
- Input voltage and maximum current (ENERGY STAR)
- the circuit voltage the unit is certified on and the most current it draws
- Vent type and size (ENERGY STAR)
- how a gas unit is vented, the vent's diameter and the height of its vent connector
What these figures mean
How this compares
The closest models in the same class — same fuel, type and draw pattern.
Keep going
How every figure on this page is calculated
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Find what replaces your water heater
Enter the model number off your old unit and see what is on file today, with the yearly cost difference.
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Find a water heater that fits
Three questions — fuel, hot water need, install space — narrow every model on file to the ones that fit.
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What a water heater costs to run
Prices a unit's efficiency against your own utility's filed tariff for your ZIP code.
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How to size a tankless water heater by GPM
Answered from what models in this size actually file.
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Water heaters
Every model on file with the Department of Energy, by heater type.
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All gas tankless water heaters
Gas-fired instantaneous units, sized by flow rate rather than tank gallons.
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Every Rheem model on file
What this brand files, by heater type.
UEF 0.96 · Grade A Price it on your ZIP
The registry does not publish a yearly energy figure; this site computes 176 therms from the registry's own data. The input is the UEF, the ratio of hot water delivered to energy used, which is 0.96 for this model. That ratio is applied to the DOE test's daily hot-water draw for the high draw pattern. The source is the DOE CCD, retrieved 2026-09-19. A household that draws more hot water than the test assumes will use more gas than 176 therms, and one that draws less will use less. The 6 therms gap to the class median is measured under the same test draw. It compares models under identical conditions rather than predicting a given home's use. Each step is set out in how the annual cost is calculated.
The high draw pattern stands for a larger household, or one where showers and laundry overlap. Among the 397 gas tankless units registered at that pattern, this model ranks 12th lowest in energy use. Its maximum flow rate in gallons per minute is 4.6, as listed in the registry. The rank and the 176 therms figure do not describe a smaller household, whose daily draw is lower than the test assumes. Figures for other draw patterns are not available for this model. Whether 4.6 covers a given set of fixtures running together is not in the registry data. Readers outside the high pattern can compare units with the selector by fuel, space and size. To match this class from a model number, use the same-class replacement search.
The running cost is not stated in this text because it depends on your state's average residential gas price. The page computes it from your ZIP, applying that price to 176 therms a year. The same rate decides what the 6 therms difference from the 182 therms median is worth in your state. The registry gives no single figure for that difference in cost. Enter your ZIP in the cost calculator for your own ZIP to see both results. The installed-cost range appears in its own block on this page, with its source and date. That range is a modeled estimate, not a quote. It is kept separate from the 176 therms figure, which covers only gas use at the test draw.
DOE CCD · 2026-09-19