One verified RTEX-24 owner mentioned adding an Aqua-Pure AP430SS water filter specifically to reduce how often they needed to flush their system, cutting their maintenance frequency from every few months down to roughly twice a year. That’s a small, practical detail that doesn’t show up in most spec sheets but matters a lot once you’re the one doing the maintenance.
Adding an inline water filter ahead of a Rheem RTEX-24 can reduce sediment and mineral intake into the unit, potentially extending the interval between descaling maintenance cycles, particularly in areas with hard or sediment-heavy water. This isn’t a required accessory, the unit functions without one, but it’s a low-cost addition that several verified owners specifically credit with reducing their long-term maintenance burden.
Why a Filter Helps a Tankless Unit Specifically
Unlike a tank water heater, where sediment settles at the bottom of a large reservoir and gets flushed out periodically, a tankless unit’s heating elements sit directly in the flow path, meaning any sediment or mineral content in your water passes directly across the elements every time you use hot water. Over time, this contributes to the same scale buildup that regular descaling is meant to address.
An inline filter installed ahead of the unit catches sediment before it ever reaches the heating elements, reducing (though not eliminating) the mineral load the elements are exposed to, and correspondingly reducing how quickly scale accumulates.
What Kind of Filter Makes Sense
A sediment filter designed for whole-house or point-of-use installation ahead of a water heater is the most directly relevant type for this purpose. These filters are rated by micron size (how fine a particle they can catch) and by flow rate capacity, which matters given the RTEX-24’s own flow demands of up to 5.9 GPM, an undersized filter could itself become a bottleneck restricting your water flow.
The Aqua-Pure AP430SS mentioned by the verified reviewer is one specific example of a sediment filtration product used successfully ahead of a tankless unit, though it’s not the only option, and your specific water conditions should guide the exact filter and micron rating you choose.
Filter vs Water Softener: Different Jobs
It’s worth being clear that a sediment filter and a water softener solve different problems. A sediment filter primarily catches physical particulate matter (sand, rust, debris) from your water supply. A water softener specifically addresses water hardness, the dissolved calcium and magnesium that cause scale buildup on heating elements, through an ion exchange process.
For hard water areas specifically, a water softener addresses the root cause of scale buildup more directly than a sediment filter alone, though many households benefit from using both together, a softener for hardness and a sediment filter for particulate matter.
Installation Considerations
An inline filter typically installs on your main water line ahead of the tankless unit, requiring basic plumbing work similar to installing any standard water filtration fitting. If you’re already having isolation service valves installed as part of your original RTEX-24 setup, it’s worth planning the filter installation at the same time to avoid a second round of plumbing work later.
Maintenance Reminder
A filter itself requires periodic replacement or cleaning, depending on the specific product, generally every few months depending on your water quality and usage volume. Don’t treat a filter as a set-and-forget solution, check manufacturer guidance for your specific filter’s replacement schedule.
For the full picture of whether a water softener specifically makes sense for your household, see our dedicated water softener guide.
Rheem RTEX-24 24kW 240V Electric Tankless Water Heater - Check Current Price on Amazon
The Bottom Line
An inline sediment filter isn’t required for the Rheem RTEX-24 to function, but several verified owners credit it with meaningfully reducing how often they need to descale the unit. It’s a modest, low-cost addition worth considering, especially in areas with sediment-heavy or hard water.
Frequently Asked Questions
Do I need a water filter for my Rheem RTEX-24? It’s not required for the unit to function, but an inline sediment filter can reduce mineral and particulate buildup on the heating elements, potentially extending the interval between descaling cycles.
What type of filter works best with a tankless water heater? A sediment filter rated for adequate flow capacity (at least matching the RTEX-24’s up to 5.9 GPM demand) installed ahead of the unit is the most directly relevant type for this purpose.
Is a water filter the same as a water softener? No, a sediment filter catches physical particulate matter, while a water softener specifically addresses water hardness through ion exchange, a different process solving a different problem.
How often does an inline water filter need to be replaced? This varies by specific product and your water quality, generally every few months, check your specific filter’s manufacturer guidance for an exact schedule.
Can a water filter reduce how often I need to descale my Rheem RTEX-24? Based on at least one verified owner’s account, yes, adding an inline filter reduced their flushing frequency from every few months to roughly twice a year.
Where does a water filter get installed relative to the tankless unit? Typically on your main water line ahead of the unit, so filtered water enters the tankless system before reaching the heating elements.
Will an undersized filter restrict my water flow? Yes, if a filter’s flow rate capacity is lower than your tankless unit’s demand, it can become a bottleneck. Choose a filter rated for at least your unit’s maximum flow rate.
Should I install a filter and a water softener together? Many households in hard water areas benefit from both, a softener addressing water hardness directly and a sediment filter catching particulate matter, working together for more comprehensive protection.
Is it worth adding a filter if I already have a water softener? It can still help catch sediment and particulate matter that a softener alone doesn’t address, particularly in areas with sediment-heavy municipal or well water.
Can I install a water filter myself? For most inline filter housings, this is a manageable DIY plumbing task similar to other common water filtration installations, though your specific setup and comfort level should guide that decision.
References
- Verified Amazon customer review describing inline water filter use with the Rheem RTEX-24, accessed July 2026: https://www.amazon.com/dp/B01MS9DVEE