Rheem tankless · updated October 26, 2026
Rheem tankless water heaters: what the box says, what winter delivers
The RETEX-27 and RETEX-36 are sold as “7 GPM” and “8 GPM”. Those flows assume the water only rises 26 °F (14 °C) and 31 °F (17 °C). With water coming in at 3 °C and 41 °C at the tap, Rheem’s own tables give 2.7 gpm and 3.6 gpm. Here is how to choose with the right numbers.
The label against cold water
Flow in US gallons per minute, 105 °F (41 °C) at the tap. Source: Rheem.
Maximum flow, for a rise of only 26 °F (14 °C)
Rheem’s table, coldest zone (37 °F)
One shower according to Rheem: 2 gpm. At this water temperature, the RETEX-27 handles one shower (2 gpm), not two.
01 · The winter check
Pick the incoming water, open your taps: Rheem’s table tells you which one keeps up
Flows from Rheem’s RH-TE-WH-SS sheet (Rev. 1, 7/26), calculated for 105 °F (41 °C) at the tap. Incoming water changes with the season and the place: pick yours.
Incoming water temperature
The 9 zones of Rheem’s table, from the coldest (37 °F) to the warmest (77 °F).
What runs at the same time
Average flow per fixture published by Rheem (2024 and 2026 sheets). Yours may differ.
What you are asking for
3.5 gpm
that is 13.2 L/min, with water coming in at 3 °C
Verdict: You need the RETEX-36: the 27 kW cannot keep up.
Bar: Rheem’s flow at this water temperature. Yellow line: your demand.
02 · The electrical service
The water heater alone draws 113 or 150 amps. Can your service keep up?
Rheem recommends a 200 A service for the 27 kW and 300 A for the 36 kW. Pick yours to see the share the water heater takes.
Your electrical service
Building voltage
A house is usually on 240 V; some buildings are on 208 V.
On a 200 A service
3 double-pole 40 A breakers, 3 circuits in 8 AWG copper wire (75 °C)
Meets the 200 A Rheem recommends4 double-pole 40 A breakers, 4 circuits in 8 AWG copper wire (75 °C)
Below the 300 A Rheem recommendsRheem values at 240 V, RH-TE-WH-SS sheet Rev. 1 (7/26); in Canada, sizing is checked at 125% of the current.
03 · The two Rheem units
Same slim cabinet, same front-panel control: the 36 kW has one more heating chamber
Each chamber has its own 9 kW element and its own breaker. Everything else is much the same.
27 kW · 3 chambers
RETEX-27
- 113 A at 240 V, 3 × 40 A double-pole
- 200 A service recommended by Rheem
- 2.7 to 6.6 gpm at 105 °F depending on incoming water
36 kW · 4 chambers
RETEX-36
- 150 A at 240 V, 4 × 40 A double-pole
- 300 A service recommended by Rheem
- 3.6 to 8.8 gpm at 105 °F depending on incoming water
| Spec | RETEX-27 | RETEX-36 |
|---|---|---|
| Power at 240 V | 27 kW | 36 kW |
| Total current at 240 V | 113 A | 150 A |
| Breakers | 3 × 40 A double-pole | 4 × 40 A double-pole |
| Wire (75 °C insulation) | 3 × 8 AWG | 4 × 8 AWG |
| Recommended electrical service | 200 A | 300 A |
| Heating chambers | 3 | 4 |
| UEF | 0.93 | 0.94 |
| Dimensions (H × W × D) | 17 × 17 × 3.625 in | 17 × 21 × 3.625 in |
| Shipping weight | 17.8 lb | 22.7 lb |
| Activation flow | 0.3 gpm | 0.3 gpm |
| Water pressure | 25–150 psi | 25–150 psi |
| Temperature setting | 26–60 °C | 26–60 °C |
| Water connections | 3/4 in NPT | 3/4 in NPT |
04 · On site
Two trades, two licences, and Rheem’s installation rules
Rheem calls for a qualified electrician and a qualified plumber. In Québec, those are two separate RBQ licence subclasses.
The electrical work
Work reserved to an electrical contractor. AirGreen holds this subclass.
- One circuit and one breaker per heating chamber: 3 for the 27 kW, 4 for the 36 kW
- A ground for every circuit, per Rheem’s manual
- Rheem lists 40 A per circuit; its manual notes that the Canadian Electrical Code generally requires 125% of the current (37.5 A per chamber, i.e. 46.9 A). Final wire and breaker sizes are the master electrician’s call.
- At start-up, water must flow before power is turned back on (Rheem)
The water connection
This part must be done by a 15.5 licence holder: AirGreen does not hold this subclass.
- 3/4 in NPT connections, inlet and outlet at the bottom
- 25 to 150 psi; a pressure-reducing valve above 150 psi
- T&P valve: not required for most installations according to Rheem, but local code may require one
- ASSE 1017 mixing valve recommended by Rheem above 125 °F (52 °C)
What Rheem requires and recommends for the installation
- Indoors only, protected from freezing: freeze damage is not covered.
- Mounted upright, with 12 in of clearance above and below, and 6 in in front and on the sides.
- No chimney or venting: it is an electric appliance.
- A drip pan or leak detector is recommended.
- Factory set at 120 °F (49 °C), adjustable from 26 to 60 °C. Chapter III – Plumbing of Québec’s Construction Code limits shower and bathtub water to 49 °C (art. 2.2.10.7).
- Hard water: water treatment is recommended, the heat exchanger is flushed regularly and the connections are inspected at least once a year. Rheem gives no set descaling interval.
05 · Warranty and programs
5 years on leaks, 1 year on parts, labour excluded
Rheem’s limited warranty for its electric tankless water heaters (form EX52, Rev. 12/19), read on October 20, 2026.
- Leaks: 5 years from the original purchase (or from moving into a new home, whichever is later).
- Parts: 1 year for a mechanical or electrical failure.
- Without a receipt, both coverages start at the manufacturing date.
- Labour, removal and on-site repair: paid by the owner.
- Original owner only. Form EX52 requires no registration; rheem.ca invites owners to register their products.
- Notable exclusions: freezing, installation not per the instructions or codes, dry firing, pressure or flow problems, unit moved from its original location.
- Warranty EX52 exists in English only; we found no Canadian version.
Programs in October 2026: none covers this water heater
Each program checked on its own site on October 26, 2026. An electric resistance water heater does not qualify, for the reasons below.
ENERGY STAR
NoWater heater specification 5.0 excludes electric resistance water heaters.
LogisVert
NoGuide v1.10 (Sept. 15, 2026) has no water heater measure.
Hilo
NoThe Hilo controller is for a tank of 30 imperial gallons or more, 50 A maximum load.
Rénoclimat
NoSince October 1, 2026, the energy-efficiency stream covers insulation, windows, backup power connection and batteries: no measure targets water heaters.
Greener Homes
ClosedThe Canada Greener Homes Grant is closed; the last day to upload documents was December 31, 2025.
Rheem at a glance
According to Rheem (rheem.com, rheem.ca, centennial e-book), read on October 20, 2026.
06 · Questions
The questions we get about Rheem tankless units
AirGreen
The right Rheem comes down to three numbers
Your electrical service, the incoming water and what runs at the same time. Send them to us: the quotation is free.
Sources checked October 20, 2026; programs rechecked October 26
Technical figures come from Rheem’s documents; programs and rules come from their official sites.
- Rheem, “Professional Classic RTEX”, sheet RH-TE-WH-SS Rev. 1 (7/26), rheem.ca
- Rheem, “PERFORMANCE RETEX Tankless Electric”, sheet THD-PTE 18-36 Rev. 1 (11/24), rheem.com
- Rheem, Canadian French sheet TK-101F (07/17): 208 V values and certifications
- Rheem, electric tankless water heater installation and owner’s manual (EN/FR/ES)
- Rheem, limited warranty for electric tankless water heaters, form EX52 Rev. 12/19
- Rheem, About page (rheem.ca), centennial e-book (rheem.com/100) and Eemax acquisition release (Dec. 14, 2015)
- ENERGY STAR, Residential Water Heaters specification 5.0 (effective April 18, 2023)
- Hydro-Québec, LogisVert guide v1.10 (September 15, 2026) and Hilo water heater controller conditions
- Government of Québec, Rénoclimat program, rules in force October 1, 2026
- Natural Resources Canada, Canada Greener Homes Grant (ended December 31, 2025)
- Québec Construction Code, Chapter III – Plumbing (NPC 2020 as amended), art. 2.2.10.7
- Québec Construction Code, Chapter V – Electricity (CEC 2021), in force March 26, 2026; RBQ subclasses 15.5 and 16
Price on quotation
Free quotation for the two models below.
