Rheem Electric Tankless Water Heater: Complete Installation, Maintenance, and Troubleshooting Guide
A Rheem electric tankless water heater delivers continuous hot water using on-demand electric heating elements, eliminating storage tanks and reducing standby energy loss. These units typically require 120V-240V power, flow rates of 0.5–6.5 GPM, and precise electrical circuitry compliant with NEC Article 422. Proper sizing, installation, and maintenance are critical for efficiency and longevity. This guide covers technical specifications, installation procedures, cost analysis, troubleshooting, and safety compliance.
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What Exactly Is a Rheem Electric Tankless Water Heater?
A Rheem electric tankless water heater is a point-of-use or whole-house water heating system that heats water instantly as it flows through the unit, using electric resistance heating elements controlled by a microprocessor. Unlike traditional tank models, it contains no stored hot water, reducing energy consumption by 20–50% depending on usage patterns. The system activates when water flow exceeds 0.5 GPM, triggering temperature sensors and modulating power to maintain setpoint accuracy within ±2°F.
Rheem’s electric tankless models include the RTE Series (point-of-use) and RTG Series (whole-house), with power inputs from 3.5 kW to 28 kW. These units use copper-sheathed heating elements and stainless steel heat exchangers to resist corrosion. Internal flow sensors and thermistors provide real-time feedback to the control board, enabling precise temperature modulation. Units are UL 499 and CSA C22.2 certified for electrical safety and performance.
These heaters require dedicated 240V circuits (for models >3.5 kW) and must be installed in dry, accessible locations per NEC Article 422 and IRC Section P2803. They are not suitable for hard water without pre-treatment, as mineral buildup can reduce efficiency and void warranties. Rheem offers both single-phase and multi-phase models, with digital thermostats allowing temperature settings between 80°F and 140°F.
Installation must follow manufacturer clearances: 12 inches above, 6 inches below, and 1 inch on sides. Venting is not required, unlike gas tankless units, making them ideal for apartments, condos, or retrofit applications. However, electrical service panels must support additional load—upgrading from 100A to 200A is common for whole-house models.
How Does a Rheem Electric Tankless Water Heater Work?
A Rheem electric tankless water heater operates by activating heating elements when water flow is detected, using sensors to modulate power output and maintain precise outlet temperatures. Cold water enters through an inlet filter, passes through a flow sensor, and triggers the control board to energize heating elements based on the temperature difference between inlet and setpoint. The system adjusts wattage in real time to deliver consistent hot water at 0.5–6.5 GPM, depending on model and incoming water temperature.
The process begins when a faucet opens, creating water flow above the activation threshold (typically 0.5 GPM). A turbine or pressure sensor detects movement and signals the control board. Simultaneously, an inlet thermistor measures incoming water temperature, while the user-set thermostat determines target output (e.g., 120°F). The control board calculates required energy input using the formula:
kW = (GPM × ΔT × 500) ÷ 3412
For example, raising 3 GPM from 50°F to 120°F requires (3 × 70 × 500) ÷ 3412 = 30.8 kW. Rheem’s RTG-28 model provides exactly 28 kW, sufficient for two showers running simultaneously in moderate climates.
Heating occurs via multiple copper-sheathed elements arranged in parallel or series. Power is delivered through double-pole circuit breakers sized per NEC Table 240.6(A)—a 28 kW unit requires a 150A breaker and 1/0 AWG copper wire. The control board uses phase-angle firing or burst-fire modulation to adjust heat output, preventing temperature spikes.
Once flow stops, the unit de-energizes within 0.5 seconds. A built-in overheat protection switch (typically 180°F) cuts power if internal temperatures exceed safe limits. Some models include self-diagnostics, displaying error codes like E3 (flow switch failure) or E5 (overtemperature).
How Do You Install a Rheem Electric Tankless Water Heater Step-by-Step?
Installing a Rheem electric tankless water heater requires electrical upgrades, plumbing connections, and compliance with NEC and local codes. The process takes 4–8 hours for a licensed electrician and plumber, with labor costs of $400–$1,200 depending on panel capacity and wall modifications. Units must be mounted vertically on load-bearing walls using included brackets, ensuring 12 inches of clearance above for service access.
Step 1: Turn Off Power and Water Supply
Shut off main electrical power at the breaker and close the main water valve. Drain existing water lines by opening faucets. Verify power is off using a non-contact voltage tester at the work area. Failure to de-energize circuits risks electrocution due to 240V exposure.
Step 2: Mount the Unit
Use a level to mark mounting points on a stud-framed wall. Drill pilot holes and secure the mounting plate with 3-inch lag screws. Hang the heater, ensuring it sits flush. Do not mount on drywall alone—this violates UL 499 structural requirements.
Step 3: Run Electrical Circuit
Install a dedicated 240V circuit from the main panel. For a 28 kW unit, use 1/0 AWG THHN copper wire in 1.25-inch EMT conduit, protected by a 150A double-pole breaker. Bond the conduit to ground per NEC Article 250. Use wire nuts rated for aluminum if connecting to aluminum service lines.
Step 4: Connect Plumbing Lines
Attach ¾-inch copper or PEX lines to inlet and outlet ports using dielectric unions to prevent galvanic corrosion. Install a sediment filter on the cold inlet to reduce mineral buildup. Include isolation valves for future servicing. Pressure test at 80 PSI for 15 minutes to check for leaks.
Step 5: Power Up and Program
Restore power and water. Open faucets to purge air. Use the digital interface to set desired temperature (recommended: 120°F). Run hot water at a faucet to confirm activation. Verify no error codes appear. Calibrate temperature if necessary using Rheem’s RTG-19/21/24/28 Setup Guide.
Rheem’s official product documentation provides model-specific wiring diagrams and clearance requirements.
Why Does a Rheem Electric Tankless Water Heater Fail to Heat Water?
A Rheem electric tankless water heater fails to heat water primarily due to power supply issues, tripped breakers, failed heating elements, or flow sensor malfunctions. Each cause produces distinct diagnostic indicators: no display means power loss, blinking lights indicate error codes, and lukewarm output suggests partial element failure. Identifying the root cause requires systematic testing of electrical, mechanical, and control components.
Loss of power is the most common issue—check the double-pole breaker in the main panel. A tripped 150A breaker often results from circuit overload or shorted heating elements. Use a multimeter to test for 240V at the unit’s terminal block. If voltage is absent, inspect wiring for loose connections or damaged insulation.
Failed heating elements occur after 7–10 years of use, especially in hard water areas. Test resistance with a multimeter: a reading of infinity (OL) indicates an open circuit. Rheem elements typically measure 10–20 ohms. Replace in pairs if one fails to prevent imbalanced loads.
Flow sensor failure prevents activation. If water flows but the unit doesn’t ignite, remove and inspect the sensor for debris. Clean the turbine with vinegar or replace if the magnet is degraded. Error code E3 points directly to flow switch issues.
Control board failure—often from power surges—requires replacement. Surge protectors rated for 40,000 amps are recommended. Units installed without whole-house surge protection have a 3× higher failure rate in lightning-prone areas like Florida or Texas.
How Much Does a Rheem Electric Tankless Water Heater Cost?
A Rheem electric tankless water heater costs $500–$1,800 for the unit and $800–$2,500 for professional installation, totaling $1,300–$4,300. Prices vary by model, power rating, and electrical service requirements. The RTE-7 (7 kW) sells for $500–$650, while the RTG-28 (28 kW) ranges from $1,200–$1,800. Installation costs depend on panel upgrades—adding a 150A subpanel adds $1,000–$1,500.
| Model | kW | GPM @ Δ70°F | Unit Price | Install Cost |
|---|---|---|---|---|
| RTE-7 | 7 | 1.0 | $500–$650 | $400–$600 |
| RTG-19 | 19 | 3.0 | $900–$1,100 | $800–$1,500 |
| RTG-28 | 28 | 4.5 | $1,200–$1,800 | $1,200–$2,500 |
Labor costs rise in regions with high electrician rates—$85/hour in California vs. $55/hour in Texas. Retrofitting older homes (pre-1980) often requires panel upgrades from 100A to 200A, costing $1,500–$3,000. Return on investment occurs in 5–7 years due to 30% lower energy bills compared to 50-gallon electric tanks.
Energy.gov estimates that tankless heaters save $100/year on average, with electric models having lower upfront costs than gas but higher operating expenses.
What Problems Might You Encounter with a Rheem Electric Tankless Water Heater?
Common problems with Rheem electric tankless water heaters include insufficient hot water, error codes, mineral buildup, electrical tripping, and cold water sandwich. Each issue stems from installation errors, water quality, or component wear. Addressing them requires preventive maintenance, proper sizing, and adherence to electrical codes.
Insufficient hot water occurs when the unit is undersized for demand. A 19 kW model can heat 3 GPM with a 70°F rise—adequate for one shower. Simultaneous use of a shower and dishwasher (4.5 GPM) exceeds capacity, causing temperature drops. Solution: Install a 28 kW unit or use staggered appliance timing.
Mineral buildup in hard water areas (over 7 GPG) coats heating elements, reducing efficiency by 15–30%. Descaling every 6–12 months with a 1-gallon vinegar flush restores performance. Install a water softener if hardness exceeds 12 GPG.
Cold water sandwich—brief bursts of cold water between uses—happens when residual hot water cools in pipes. Fix by installing a recirculation pump with a dedicated return line or using point-of-use units near bathrooms.
Electrical tripping results from overloaded circuits or failing elements. A 28 kW unit draws 117 amps—exceeding a 100A service. Upgrade the panel before installation. Use AFCI/GFCI breakers per NEC 210.8 to prevent fire hazards.
Error codes like E1 (ignition failure), E3 (flow sensor), or E5 (overheat) require reset procedures and component testing. E5 often indicates poor ventilation or blocked inlet filters.
Which Rheem Electric Tankless Model Is Best for Your Home?
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Choosing the best Rheem electric tankless model depends on household size, water usage, inlet temperature, and electrical capacity. For 1–2 occupants with moderate use, the RTE-7 or RTG-13 suffices. For 3+ occupants, the RTG-19 or RTG-28 is required. Key factors include flow rate, temperature rise, and circuit availability.
In northern climates (inlet water 38–45°F), a 28 kW unit is essential to achieve 120°F at 4 GPM. In southern regions (inlet 60–70°F), a 19 kW unit may suffice. Use Rheem’s online sizing calculator or apply the formula:
Required kW = (Total GPM × ΔT) × 0.00208
Example: 4 GPM × (120°F – 45°F) × 0.00208 = 31.2 kW → choose RTG-28 (28 kW, closest available).
Point-of-use models (RTE-7, RTE-11) serve sinks or showers within 10 feet of the unit, reducing wait time and pipe heat loss. Whole-house models (RTG-19, RTG-28) centralize heating but require larger circuits.
Check electrical service: a 200A panel is mandatory for RTG-28. Older homes may need utility-approved upgrades. Consult a licensed electrician to evaluate load calculations per NEC Article 220.
The RTG-28 is available at Home Depot with professional installation options.
How Do You Maintain a Rheem Electric Tankless Water Heater?
Maintaining a Rheem electric tankless water heater involves biannual descaling, filter cleaning, visual inspections, and error code monitoring to ensure 15–20 year lifespan. Neglect reduces efficiency by 25% and increases failure risk. Follow Rheem’s PM-100 Maintenance Protocol for optimal performance.
Descaling requires a 1-gallon pump kit and 4 quarts of white vinegar. Shut off power and water. Connect hoses to inlet/outlet valves, circulate vinegar for 45 minutes, then flush with clean water. Perform every 6 months in hard water areas, annually in soft water.
Clean the inlet filter monthly by shutting off water, unscrewing the cold inlet union, and rinsing the mesh screen. Clogged filters trigger low-flow error codes and reduce output.
Inspect wiring annually for loose terminals or corrosion. Tighten lugs to 25 in-lbs torque. Check ground continuity with a multimeter—resistance must be <1 ohm.
Monitor for error codes after heavy usage. E3 (flow sensor) often clears after filter cleaning. Persistent E5 (overheat) requires professional diagnosis.
Keep installation area dry and unobstructed. Ambient temperatures must stay above 32°F to prevent freeze damage. Units have freeze protection down to 14°F if powered, but power loss risks burst pipes.
FAQ
#### Why does my Rheem electric tankless heater display error code E3?
Error code E3 indicates a flow sensor malfunction, typically caused by debris in the turbine, low water pressure, or a faulty sensor. Clean the inlet filter and check for minimum 20 PSI supply pressure. If the issue persists, replace the flow sensor assembly. Ensure water flow exceeds 0.5 GPM to activate the unit. Test with a multimeter for continuity—open circuit means replacement is needed.
#### How much does it cost to install a Rheem electric tankless water heater?
Installation costs $800–$2,500, including $500–$1,800 for the unit and $300–$700 for labor. Costs rise if electrical panel upgrades are needed—adding a 150A circuit to a 100A service costs $1,000–$1,500. Regional labor rates vary: $55/hour in Texas, $85/hour in California. Total project cost ranges from $1,300 to $4,300 depending on model and home infrastructure.
#### Are Rheem electric tankless water heaters safe for homes with children?
Yes, but set the thermostat to 120°F to prevent scalding. Water above 125°F can cause third-degree burns in 30 seconds. Rheem units have built-in anti-scald protection and overheat sensors. Install thermostatic mixing valves at showers for added safety. Keep digital controls locked to prevent tampering. Units are grounded and require GFCI protection per NEC 210.8.
#### How does a Rheem electric tankless compare to gas tankless models?
Electric models have lower upfront costs ($1,300 vs. $2,500) and no venting requirements, but higher operating costs—$550/year vs. $270 for gas. Gas units provide higher flow rates (up to 11 GPM) and perform better in cold climates. Electric models are easier to install in apartments but require 200A service for whole-house units. Choose electric for retrofits, gas for high-demand homes.
#### Can I install a Rheem electric tankless water heater myself?
DIY installation is not recommended due to 240V wiring, load calculations, and permit requirements. Mistakes risk fire, electrocution, or code violations. Only licensed electricians should handle circuits over 30A. Plumbers must ensure dielectric connections and pressure testing. DIY voids Rheem’s warranty unless done by a professional. Hire a Rheem Pro Partner for warranty validation.
#### How often should I descale my Rheem electric tankless water heater?
Descaling is required every 6–12 months, depending on water hardness. In areas over 7 GPG, flush every 6 months using 1 gallon of vinegar and a circulation pump. In soft water (under 3 GPG), annual maintenance suffices. Signs of scale include reduced flow, error codes, and longer wait times. Use only food-grade vinegar—avoid muriatic acid, which damages sensors.
#### What size circuit breaker do I need for a Rheem RTG-28?
The RTG-28 requires a 150A double-pole circuit breaker and 1/0 AWG copper wire. This complies with NEC Table 310.16 and Article 422. The unit draws 117 amps at 240V. Use a UL-listed breaker rated for continuous loads. Install in a 200A panel—older 100A services must be upgraded. Conduit must be 1.25-inch EMT for wire fill compliance.
#### Do Rheem electric tankless water heaters have a warranty?
Yes, Rheem offers a 10-year limited warranty on heat exchangers and 1–3 years on parts, depending on model registration. Labor is covered for 1 year. Warranty requires professional installation and annual maintenance. Register online within 60 days. Exclusions include hard water damage without filtration and DIY installations. Extended warranty options are available through dealers.
Conclusion
A Rheem electric tankless water heater provides energy-efficient, continuous hot water when properly sized, installed, and maintained. Key success factors include accurate load calculation, 200A electrical service for whole-house models, and biannual descaling in hard water areas. Units like the RTG-28 deliver 4.5 GPM at Δ70°F, suitable for 3–4 occupants. Installation must follow NEC Article 422, IRC P2803, and manufacturer clearances.
Prioritize professional installation to ensure code compliance and warranty validity. Monitor for error codes, maintain inlet filters, and schedule vinegar flushes every 6–12 months. Compare operating costs—electric models cost more to run than gas but have lower installation complexity. For optimal performance, pair with a water softener in high-mineral areas.
Upgrade from a traditional tank to save 30% on energy bills, reclaim floor space, and gain endless hot water. Consult a Rheem Pro Partner for site evaluation, load calculation, and permit handling.
Placement: After “How Do You Maintain…”