The single most repeated phrase across verified Rheem RTEX-24 reviews isn’t about hot water at all, it’s about breakers. Reviewer after reviewer describes checking their panel, discovering they didn’t have room, and bringing in an electrician before ever turning the unit on. This article exists because that step deserves more attention than a single bullet point on a product listing.
The Rheem RTEX-24 requires three 40-amp double-pole breakers on a 240V circuit, with Rheem recommending 200-amp household electrical service to support the load safely. This is a substantial electrical requirement compared to most household appliances, and confirming your panel can support it before purchase is the single most important step in avoiding a costly surprise.
Why Electric Tankless Heaters Need So Much Power
Unlike a tank water heater, which heats water slowly over time and stores it, a tankless unit has to heat water instantly as it flows through, which requires a large burst of power on demand. The RTEX-24’s 24kW rating reflects that: it’s built to raise the temperature of up to 5.9 gallons of water per minute, and doing that requires serious electrical capacity.
Rheem’s three-element design splits that load across three separate double-pole 40-amp circuits rather than one massive circuit, partly for safety and partly to enable the self-modulating feature, where the unit only activates the elements needed for current demand rather than always running at full power.
What “3 x 40 Amp Double Pole” Actually Means
A double-pole breaker protects a 240V circuit (as opposed to a standard single-pole breaker for 120V household outlets). The RTEX-24 needs three of these, each rated for 40 amps, meaning your panel needs three open slots specifically capable of accepting double-pole breakers of that rating, not just three generic open spaces.
This is different from adding a single new appliance circuit. You’re effectively adding the electrical equivalent of three separate 240V circuits, which is why Rheem explicitly recommends 200-amp household service, a standard many homes already have, but not universal, particularly in older houses.
Checking Your Panel Before You Buy
Before purchasing, physically open your electrical panel (or have an electrician do it) and confirm:
Your total household service rating. Rheem recommends 200-amp service; if your home has 100 or 150-amp service, adding this load may require a service upgrade from your utility company, a bigger and more expensive project than just adding breakers.
Available double-pole breaker slots. You need three open slots specifically rated for 40-amp double-pole breakers, or a way to safely add them, sometimes by adding a sub-panel or auxiliary breaker box.
Your panel’s total amperage headroom. Even with open slots, your panel needs enough unused capacity across your total electrical load to safely add another 100 amps of potential draw (the RTEX-24’s rated amperage per Rheem’s own product listing) without exceeding the panel’s overall rating.
What Happens If Your Panel Isn’t Ready
Based on real verified reviewer experiences, the most common solutions when a panel doesn’t have adequate capacity include:
Adding an auxiliary breaker box or sub-panel specifically for the new circuits, which one detailed reviewer needed alongside their main electrical work.
Upgrading your main electrical service entirely, a larger project involving your utility company, needed if your home’s total service rating (not just panel slots) is insufficient.
Running larger gauge wire and larger conduit than a simpler appliance would need. One verified reviewer specifically used 8-gauge wire and 1-inch conduit to accommodate the nine total wires required for three double-pole circuits.
General Electrical Code Context
The National Fire Protection Association (NFPA), which publishes the National Electrical Code (NEC) used as the basis for electrical codes across the United States, notes that residential electrical services must be sized based on total home load, with major appliances factored into that calculation directly (NFPA, “5 Key Considerations for Single Family Residential Electrical Services Based on the 2020 NEC,” Corey Hannahs, 2022). This is general code context rather than RTEX-24-specific guidance, but it explains why adding a high-draw appliance like a whole-home tankless heater often triggers a broader look at your total panel capacity, not just a simple breaker swap.
When to Call an Electrician vs Do It Yourself
Given the amperage and voltage involved, this is not a reasonable DIY project unless you are a licensed electrician yourself. Multiple verified reviewers, including ones with significant general handiness, specifically describe bringing in professional electricians for this exact reason, with one stating plainly they “would have been afraid to try and do this myself even with all my experience.”
For the full step-by-step installation process beyond just the electrical piece, see our complete installation guide.
Rheem RTEX-24 24kW 240V Electric Tankless Water Heater - Check Current Price on Amazon
The Bottom Line
The Rheem RTEX-24’s electrical requirements, three 40-amp double-pole breakers on 240V circuits with 200-amp service recommended, are substantial enough that confirming your panel’s capacity before purchase should be your very first step, not an afterthought discovered mid-installation.
Frequently Asked Questions
How many amps does the Rheem RTEX-24 need? The RTEX-24 requires three 40-amp double-pole breakers, with Rheem recommending 200-amp household electrical service overall.
Can my existing electrical panel handle a Rheem RTEX-24? It depends on your panel’s total capacity and available double-pole breaker slots. Check with a licensed electrician to confirm before purchasing, since insufficient capacity may require a panel upgrade.
What is a double-pole breaker? A double-pole breaker protects a 240V circuit by using two connected breaker switches, as opposed to a single-pole breaker used for standard 120V household outlets.
Do I need 200 amp electrical service for the Rheem RTEX-24? Rheem recommends 200-amp household service to safely support the RTEX-24’s electrical demand, though your specific home’s total load calculation should be confirmed by an electrician.
What wire gauge does the Rheem RTEX-24 need? Based on verified installations, 8-gauge copper wire is commonly used for each of the three required circuits, though your electrician should confirm the exact specification for your installation.
What happens if my panel doesn’t have enough capacity for the Rheem RTEX-24? You may need to add an auxiliary breaker box, install a sub-panel, or in some cases upgrade your main electrical service, all of which add cost beyond the unit price itself.
Can I add the required circuits myself? This work involves high-voltage, high-amperage circuits and is not recommended as a DIY project unless you are a licensed electrician, given the safety risks involved.
Why does the Rheem RTEX-24 need three separate breakers instead of one? The unit uses three separate heating elements to enable self-modulating power draw, meaning it only activates the elements needed for current demand, which requires three separate circuits.
How much does it cost to add the required electrical capacity? Real reviewer-reported costs for the full electrical installation, including labor, commonly range from $500 to $900, more if a panel upgrade or sub-panel is required.
Is it safe to install a tankless water heater without checking electrical capacity first? No. Confirming adequate electrical capacity before purchase is the most important step in avoiding costly complications, since undersized panels can require significant additional electrical work to correct.
References
- Rheem RTEX-24 official electrical requirements, Amazon.com manufacturer content, accessed July 2026: https://www.amazon.com/dp/B01MS9DVEE
- NFPA, “5 Key Considerations for Single Family Residential Electrical Services Based on the 2020 NEC,” Corey Hannahs, January 6, 2022: https://www.nfpa.org/News-Blogs-and-Articles/Blogs/2022/01/06/Considerations-for-Single-Family-Residential-Electrical-Services-Based-on-the-2020-NEC
- Verified Amazon customer reviews detailing real electrical installation experiences, accessed July 2026