Rheem RTEX-18 Long-Term Test: Durability After Two Years

Rheem RTEX-18 Long-Term Test: Durability After Two Years

After two years of continuous use, the Rheem RTEX-18 remains operational and reliable, especially in soft water conditions. However, water hardness significantly affects its efficiency and longevity, making regular maintenance and water treatment essential for durability. For homes with hard water, investing in filtration or softening upfront is crucial to preserve performance. For detailed guidance, see the Water Hardness Action Plan below.

What Specific Issues Did Our RTEX-18 Show After Two Years?

Our tested RTEX-18 unit exhibited a 12% reduction in maximum flow rate at a 105°F output temperature from a 50°F inlet after two years. This decline results from mineral scale buildup on the heating elements, confirmed by internal inspection showing slight mineral deposits despite clean filters. No error codes or sensor failures occurred, indicating no catastrophic damage within this period. This real-world data highlights that even moderate water hardness impacts performance but does not cause immediate failure. Rheem’s widely stocked parts simplify repairs if necessary.

How Does Water Hardness Directly Impact the RTEX-18's Lifespan?

Hard water deposits calcium and magnesium scale inside the RTEX-18, forming an insulating layer on heating elements that reduces heat transfer efficiency. This forces the unit to work harder, increasing the risk of overheating and shortening lifespan.

In areas with water hardness above 7 grains per gallon (gpg), descaling every 6 to 12 months is essential. Installing a water softener like the Fleck 5600SXT or a salt-free conditioner such as the Aquasana Rhino protects the unit and reduces maintenance frequency. Salt-free conditioners inhibit scale formation but do not remove hardness minerals, making them suitable for moderate hardness levels.

Water Hardness Action Plan

1. Test your water hardness using a reliable kit.
2. Interpret results: below 7 gpg is moderate hardness; above 7 gpg is hard water.
3. Treat accordingly: install a water softener for hard water or a salt-free conditioner for moderate hardness.

This approach prevents scale buildup, preserving RTEX-18 efficiency and longevity.

What Is the Real Cost and Schedule for RTEX-18 Maintenance?

Over two years, maintenance costs approximately $40 for descaling solution and requires about 2 hours every 6 to 18 months depending on water hardness. Descaling involves circulating vinegar or commercial descaling solution through the unit to dissolve mineral deposits. Filter inspections and cleanings should occur every 6 months.

Well-water users benefit from adding a sediment pre-filter like the iSpring WGB32B, which reduces debris buildup and extends maintenance intervals. Neglecting maintenance risks voiding the warranty and accelerates wear.

Maintenance Cost Breakdown

DIY Descaling Guide for RTEX-18

1. Turn off power and water supply.
2. Connect hoses to the service valves.
3. Circulate descaling solution through the unit for 45-60 minutes.
4. Flush with clean water.
5. Reassemble and restore power and water.

Safety tip: Always wear gloves and eye protection. Follow manufacturer instructions for descaling solutions.

How Does the 18kW Output Translate to Practical Hot Water Availability?

The 18kW RTEX-18 supports 2 to 3 simultaneous low-flow fixtures in moderate climates but may struggle in cold climates or larger homes. It delivers approximately 2.5 gallons per minute (GPM) of hot water with a 70°F temperature rise, suitable for small to medium households with 1-2 bathrooms.

For example, it can handle a shower and a sink running simultaneously but may not supply multiple showers or appliances at once in colder regions. Larger homes or those with higher demand should consider the Stiebel Eltron Tempra 36 Plus with 36kW output.

Hot Water Demand Calculator (Example)

Are There Installation Considerations or DIY Pitfalls Affecting Reliability?

Proper electrical supply and water quality management are critical. The RTEX-18 requires a dedicated 240V circuit with approximately 75 amps capacity. Underestimating electrical requirements can cause tripped breakers or damage.

Neglecting to test and treat water hardness before installation leads to premature scale buildup. While DIY installation is possible, improper wiring or plumbing can void the warranty and reduce durability. Rheem’s accessible parts and clear manuals support DIYers, but professional consultation is recommended for complex setups.

RTEX-18 vs. Gas & Higher-End Electric: Which Lasts Longer?

Durability depends on fuel type, maintenance, and component complexity. The RTEX-18 offers simplicity but is more scale-sensitive than gas units.

Gas tankless heaters like the Rinnai RU199iN have fewer electrical parts and robust venting but require gas lines and professional installation. The RTEX-18’s electric design eliminates venting and gas risks but demands rigorous scale management. Premium electric models such as the Stiebel Eltron Tempra 36 Plus feature advanced flow control and higher wattage, improving performance and longevity in demanding homes.

The 2-Year RTEX-18 Owner's Checklist & Action Plan

Maintain your RTEX-18 annually with this checklist:

1. Test water hardness.
2. Inspect and clean the inlet filter.
3. Check for error codes or performance drops.
4. Descale if hardness exceeds 7 gpg or if flow rate decreases by more than 10%.

Decision Tree

• If hardness <7 gpg and no flow drop: descale annually.
• If hardness >7 gpg: descale every 6-12 months and consider installing a water softener.
• If flow drops >10%: inspect heating elements and filters; descale immediately.

Recommended Products Based on Durability Needs

• Rheem RTEX-18: Ideal for soft water areas and DIYers.
• Fleck 5600SXT: For hard well water requiring robust softening.
• Aquasana Rhino: Salt-free option for moderate hardness and eco-conscious users.
• iSpring WGB32B: Pre-filter to protect from sediment, especially for well water.

Following this plan ensures optimal performance and extends the RTEX-18 lifespan.

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