What it delivers
The Rheem RTEX-18 Electric Tankless Water Heater is a whole-house electric tankless rated at 18 kW on 240 volts. Its listing gives a maximum flow of 4.4 GPM.
Worked out from its input, it delivers roughly 2.7 GPM when the water only has to rise 45°F, and 1.8 GPM at a 70°F winter rise: 1 shower at 2 GPM in summer, less than one 2 GPM shower in winter. Check your house in the planner.
At 240 volts 18 kW is about 75 amps. A licensed electrician confirms the panel, the service and the wire before it goes in.
No flue, no gas line and a compact box on the wall; the trade-off is that a cold winter inlet cuts its flow sharply.
Other listed details: features: LED Display; connections: 3/4 inch NPT; material: Stainless Steel; model: RTEX-18.
The listing gives dimensions of 14.5 in (W) x 18.25 in (H), a weight of 14.8 lb and fittings, aerators in the box.
Right unit for this house?
Install it when
- One shower at a time in mild climates
- Homes with no gas service
Look at another unit when
- Panels without spare capacity
- More than 1 shower at once in cold winters
Strengths and trade-offs
Strengths
- 18 kW
- Up to 4.4 GPM
- No venting or gas line
Trade-offs
- Draws about 75 A
- Winter flow is much lower
- Breaker needs not stated
Install limits
- Figures are the maker's or seller's own. Flow at a rise is our estimate from the input; gas, venting and electrical work needs a licensed professional.
Rated performance
Every figure below comes from the source shown in brackets. Where the maker doesn't state something, we say so instead of estimating.
| Model number | RTEX-18 | Retailer |
|---|---|---|
| Dimensions (seller) | 14.5"W x 18.25"H | Retailer |
| Features (seller) | LED Display | Retailer |
| Power | 18 kW | Retailer |
| Voltage | 240 V | Retailer |
| Max flow (maker) | 4.4 GPM | Retailer |
| Product weight | 14.8 lb | Retailer |
| Material | Stainless Steel | Retailer |
| Connections | 3/4 inch NPT | Retailer |
Rival units at this flow
More electric tankless water heaters rated for similar demand
- Stiebel Eltron Tempra 20 Trend 19.2 kW Electric Tankless Water Heater
- Stiebel Eltron Tempra 24 Trend 24 kW Electric Tankless Water Heater
- WINTEMP WM27V 27 kW Electric Tankless Water Heater
- ThermoMate EH270 27 kW Electric Tankless Water Heater
Full electric tankless water heaters spec grid · Every Rheem unit in the catalog
Final verdict
A sensible whole-house electric tankless for one shower at a time in mild climates.
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