Whole house electric tankless
Rheem RTEX-13 13kW Specifications
Researched from the DOE test procedures, NFPA 54 and NEC code tables, and manufacturer specifications. Updated .
Quick answer
This page collects what is actually published about the Rheem RTEX-13 13kW and shows what those figures produce, computed rather than transcribed. Anything the listing does not publish is not filled in with an estimate.
Published specifications
Everything here is taken from the listing or the manufacturer, and nothing is inferred.
| Specification | Value |
|---|---|
| Kw | 13 |
| Volts | 240 |
Published standard Source: Manufacturer listing data. A specification not listed here is one this listing does not publish. Check the installation manual for the full data plate.
Flow across the temperature rise range
Computed from the published input rating with the energy relation, so these figures cannot disagree with the calculators on this site.
| Temperature rise | Flow | Inlet needed for a 120 F outlet |
|---|---|---|
| 35 F | 2.5 GPM | 85 F |
| 45 F | 1.9 GPM | 75 F |
| 60 F | 1.4 GPM | 60 F |
| 70 F | 1.2 GPM | 50 F |
| 80 F | 1.1 GPM | 40 F |
| 90 F | 1 GPM | 30 F |
Published standard Source: Energy relation applied to the published 13 kW input at 98 percent efficiency. An electric unit converts essentially all its input to heat, so these figures track the manufacturer curve more closely than a gas unit does.
What circuit it needs
At 13 kW and 240 volts this draws 54.2 amps. NEC 422.13 treats it as a continuous load, so the circuit is sized at 125 percent, giving 67.7 amps of design load.
That means a 70 amp double pole breaker and 4 AWG copper. Confirm the circuit count against the installation manual, and see the breaker and wire page for 13 kW, the nearest rating worked through in full.
How it sits against the rest of its category
Other whole house electric tankless in this catalog: Rheem RTEX-18 18kW, Rheem RTEX-24 24kW, Rheem RTEX-27 27kW, Rheem 8kW Multi Fixture.
Compare them on input rating and on the figures the manufacturer actually publishes rather than on the headline number in the listing title, which in this category is frequently a maximum measured under conditions the listing never states.
Other whole house electric tankless
Rheem RTEX-18 18kW
$438.00Eighteen kilowatts draws 75 amps across two circuits. This is the largest electric tankless a typical 200 amp service absorbs without a load calculation fight.
Best for: The realistic ceiling on a 200 amp service
Check price on Amazon
Rheem RTEX-24 24kW
$549.00Twenty four kilowatts is 100 amps of continuous load. Read that number before reading the price, because the service upgrade costs more than the heater.
Best for: Houses with service capacity already proven
Check price on Amazon
Rheem RTEX-27 27kW
$689.99Three heating chambers and 112.5 amps of draw. A unit like this is a service upgrade with a water heater attached to it.
Best for: Cold inlet regions with a 400 amp service
Check price on AmazonFrequently asked questions
- What are the specifications of the Rheem RTEX-13 13kW?
- The listing publishes kw, volts and related figures, shown in full in the table on this page. Anything not shown is something the listing does not publish, and this page does not estimate it.
- What circuit does the Rheem RTEX-13 13kW need?
- It draws 54.2 amps at 240 volts, which becomes 67.7 amps of design load under the NEC continuous load rule. That means a 70 amp double pole breaker with 4 AWG copper. Confirm against the installation manual.
- Is this page based on hands-on testing?
- No, and we never claim otherwise. Everything here is compiled from the manufacturer listing, published specifications and the energy relations that turn those specifications into flow and recovery figures. We do not test products in person. Where a figure is not published, this page says so rather than estimating it.
- Are the prices on this page current?
- They come from verified catalog data at the time the page was built, and prices in this category move often. Treat any price shown as a guide and check the listing itself before deciding. Availability moves even faster than price does on water heater accessories in particular.
Turn the breaker off before touching an element. Both legs of a 240 volt circuit are live, so switching one of them off is not enough, and testing with a meter before you touch anything is the habit that matters. Never energise an element that is not submerged: dry firing destroys an element in seconds and can crack the tank lining around it.