How many amps does the Rheem RTEX-24 draw?

The RTEX-24 is rated 24 kW at 240 V, which is 100 A of continuous current using P = I x V. NEC 422.13's continuous-load rule adds a 125 percent factor for circuit and breaker sizing, which brings the design load to 125 A. An electrician sizes the wire and breaker to 125 A, not to the 100 A running current.

Can a 200 amp panel handle the Rheem RTEX-24?

Sometimes, but only after a licensed electrician runs a full load calculation. A 200 A panel needs 125 A of spare design-load capacity for this unit alone, which leaves only 75 A for every other circuit in the house before other continuous loads are even subtracted. Many existing panels with a range, dryer, and central air already installed will not clear that math.

How much flow does the RTEX-24 deliver at different temperature rises?

Calculated from its published 24 kW rating, the RTEX-24 works out to about 4.59 GPM at a 35°F rise, 2.92 GPM at a 55°F rise, and 2.14 GPM at a 75°F rise. These are calculated ceilings from the nameplate figure, not a manufacturer flow curve, so treat them as an upper bound rather than a guaranteed shower flow.

What is the difference between the RTEX-18 and the RTEX-24?

The RTEX-24 adds 6 kW over the RTEX-18, which raises current draw from 75 A to 100 A and NEC design load from 93.75 A to 125 A. In exchange, calculated flow rises across every temperature rise, for example about 2.92 GPM versus 2.19 GPM at a 55°F rise. The tradeoff is a meaningfully bigger ask of the panel.

How many circuits does the RTEX-24 need?

Rheem's installation manual specifies the exact circuit split for the RTEX-24, and that number is not published in the product listing. Electric tankless units above roughly 14 kW are commonly split across two or three smaller circuits rather than run on one, so plan for multiple breakers and confirm the precise count against the manual before an electrician wires it.

Does the RTEX-24 publish a UEF rating?

No. The product listing for the RTEX-24 does not state a Uniform Energy Factor figure. Electric tankless units as a category tend to score well on the DOE UEF scale since they have no standby or flue losses, but that is a category tendency, not a published number for this specific model.

Tankless Electric

Rheem RTEX-24 Review: Read the 100 Amp Draw Before the Price

Researched from the DOE test procedures, NFPA 54 and NEC code tables, and manufacturer specifications. Updated 2026-09-17.

Quick answer

The Rheem RTEX-24 is rated 24 kW at 240 V, which draws 100 A continuously and needs 125 A of design-load capacity under NEC 422.13's continuous-load rule. It suits a house with a confirmed 200 A or larger service and headroom already proven by an electrician's load calculation; it does not suit a panel that has not been checked, since 125 A is most of what a 200 A service has to give in the first place.

The RTEX-24 is one size up from Rheem's RTEX-18, and the step is not small. Six more kilowatts raises the continuous draw from 75 A to 100 A and the NEC design load from 93.75 A to 125 A, which on a 200 A panel is most of the service the moment every other circuit in the house is added back in.

This is not a unit to shop by price or by brand reputation first. It is a unit to shop by whatever number a licensed electrician's load calculation returns for the panel it would go on.

What do the RTEX-24's specifications actually say?

Rheem publishes 24 kW and 240 V for this model. The amperage and design load below are calculated from those two figures, not a separate published spec.

RTEX-24 electrical draw, calculated from the published nameplate rating
Specification	Value
Nameplate rating (published)	24 kW at 240 V
Current draw (I = P / V)	100 A
NEC 422.13 continuous-load factor	125 percent of nameplate draw
Design load for circuit and breaker sizing	125 A
Number of circuits	Specified in Rheem's installation manual, not published in this listing. Units above roughly 14 kW are typically split across two or three circuits.

Published standard Source: Nameplate kW and V from the product listing; amperage and design load calculated with P = I x V and NEC 422.13's 125 percent continuous-load rule.. 125 A of design load on a 200 A panel leaves 75 A for literally everything else in the house, before a load calculation even starts subtracting other continuous loads.

How much flow does the RTEX-24 deliver, and what does temperature rise cost you?

The extra kilowatts over the RTEX-18 buy real flow, but the same rise-versus-flow tradeoff still applies. Figures below are calculated from the nameplate rating, not a manufacturer flow curve.

RTEX-24 calculated flow by temperature rise
Temperature rise	Calculated flow (GPM)
35°F	4.59
45°F	3.57
55°F	2.92
65°F	2.47
75°F	2.14

Published standard Source: Calculated from the published 24 kW nameplate rating using GPM = kW x 3412 x 0.98 / (rise x 8.33 x 60). Not a manufacturer flow curve.. Run your actual inlet temperature through the temperature rise calculator before assuming a row on this table applies to your house.

Who does the RTEX-24 suit?

This unit suits a household that has already had a licensed electrician confirm 125 A of spare design-load capacity on the panel, which in practice usually means a 200 A service that is not already carrying an electric range, electric dryer, and central air simultaneously, or a larger service. It suits a two to three bathroom house in a mild to moderate climate, where a 35°F to 45°F rise puts calculated flow at 3.57 to 4.59 GPM, enough for two fixtures at once with margin.

Who should not buy the RTEX-24?

Anyone shopping this on price alone, before an electrician has looked at the panel, should not buy it yet. A cold-inlet household running a 65°F to 75°F rise should expect only 2.14 to 2.47 GPM calculated, which supports one shower well but not two at once. And a home already close to its panel's rated capacity from other continuous loads should treat 125 A as the number that likely forces a service upgrade rather than a simple circuit addition.

What does installing the RTEX-24 actually involve?

The starting point is the same load calculation described for the RTEX-18, scaled up: 125 A of design load has to fit the panel's remaining capacity after every other load is counted. Rheem's installation manual specifies how the unit's circuits split, and the electrician sizes conductor and breaker to that split under NEC Table 310.16. On a panel without the spare capacity, a subpanel or full service upgrade is the electrician's call to make and quote; houseprojectcalc.com covers that cost question, which this page does not.

Turn the breaker off and verify with a meter before opening the unit. A 24 kW electric tankless heater carries two or more energized 240 V circuits, and each one needs its own verification, not just the first breaker found.

How we researched this

We did not test this heater in person. This review is built from Rheem's published 24 kW and 240 V nameplate rating, current and design-load figures calculated from that rating with Ohm's law and NEC 422.13, and the flow table above, calculated the same way. We read the consensus of verified owner reviews for reliability and install feedback, and we say plainly where a figure, such as the circuit count or a UEF rating, is not published rather than guess at it.

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Frequently asked questions

How many amps does the Rheem RTEX-24 draw?: The RTEX-24 is rated 24 kW at 240 V, which is 100 A of continuous current using P = I x V. NEC 422.13's continuous-load rule adds a 125 percent factor for circuit and breaker sizing, which brings the design load to 125 A. An electrician sizes the wire and breaker to 125 A, not to the 100 A running current.
Can a 200 amp panel handle the Rheem RTEX-24?: Sometimes, but only after a licensed electrician runs a full load calculation. A 200 A panel needs 125 A of spare design-load capacity for this unit alone, which leaves only 75 A for every other circuit in the house before other continuous loads are even subtracted. Many existing panels with a range, dryer, and central air already installed will not clear that math.
How much flow does the RTEX-24 deliver at different temperature rises?: Calculated from its published 24 kW rating, the RTEX-24 works out to about 4.59 GPM at a 35°F rise, 2.92 GPM at a 55°F rise, and 2.14 GPM at a 75°F rise. These are calculated ceilings from the nameplate figure, not a manufacturer flow curve, so treat them as an upper bound rather than a guaranteed shower flow.
What is the difference between the RTEX-18 and the RTEX-24?: The RTEX-24 adds 6 kW over the RTEX-18, which raises current draw from 75 A to 100 A and NEC design load from 93.75 A to 125 A. In exchange, calculated flow rises across every temperature rise, for example about 2.92 GPM versus 2.19 GPM at a 55°F rise. The tradeoff is a meaningfully bigger ask of the panel.
How many circuits does the RTEX-24 need?: Rheem's installation manual specifies the exact circuit split for the RTEX-24, and that number is not published in the product listing. Electric tankless units above roughly 14 kW are commonly split across two or three smaller circuits rather than run on one, so plan for multiple breakers and confirm the precise count against the manual before an electrician wires it.
Does the RTEX-24 publish a UEF rating?: No. The product listing for the RTEX-24 does not state a Uniform Energy Factor figure. Electric tankless units as a category tend to score well on the DOE UEF scale since they have no standby or flue losses, but that is a category tendency, not a published number for this specific model.

Verify the panel with an electrician's load calculation before this unit is ordered, not after it arrives. Turn the breaker off and confirm with a meter before opening the box, since both legs of a 240 V circuit stay live even when one pole looks switched off, and never energize an element that is not fully submerged.