One is non-condensing, the other is condensing - that single difference drives most of the practical gap between these two lines.
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Quick answer
The RE series is a non-condensing tankless water heater while the SENSEI RU series is a condensing model, and that distinction drives nearly every practical difference between them - venting material, exhaust handling, and how each one fits into an existing home's setup. Neither is universally better; the right choice depends on your venting situation, whether you're doing a straight swap or a full new install, and your household's hot water demand.
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A non-condensing unit like the RE series exhausts combustion gases while they're still hot, which means it needs venting material rated for higher exhaust temperatures and doesn't produce acidic condensate that needs draining. A condensing unit like the SENSEI RU series captures additional heat from the exhaust with a secondary heat exchanger before venting it, which lets it use different venting material but also means it produces condensate that has to be managed with a drain. Neither approach is inherently better engineering - they're different ways of handling the same combustion process, with different practical requirements on the install side.
| RE series (non-condensing) | SENSEI RU series (condensing) | |
|---|---|---|
| Exhaust temperature | Higher, needs heat-rated venting material | Lower, different venting material permitted |
| Condensate | None produced | Produced, needs a drain path |
| Typical retrofit fit | Straightforward where existing venting matches | May need a condensate drain added |
| Equipment type | Non-condensing tankless line | Condensing tankless line |
If you're replacing an existing RE series unit in the same location, keeping the same non-condensing venting is often the simpler path. If you're doing a new install from scratch with no existing venting to match, that's when the condensing option becomes a genuinely open comparison rather than a constrained one.
For a straight swap of an existing RE series unit where the venting is already in place and in good condition, staying with the same non-condensing line often avoids the added complexity of routing a new condensate drain, particularly in an install location without an easy nearby drain point. For a new install with no existing venting constraints - a new build, a full mechanical room renovation, or a location with easy access to a floor drain - the condensing option opens up more flexibility on venting material and routing.
Household hot water demand is a separate question from condensing versus non-condensing, and it's worth having a technician size either option to your actual usage pattern rather than choosing based on venting convenience alone if demand and venting point in different directions.
We don't have manufacturer efficiency percentages, BTU ratings, or specific model figures to compare here, and we won't invent them - Rinnai publishes those specifications and they change across production runs, so the current numbers for your specific model belong in Rinnai's own documentation, not in a general comparison article. What we can speak to from the field is install practicality, venting fit, and what a technician actually sees when servicing each line over time.
CANRO is not an authorized or factory Rinnai dealer - we're a licensed Metro Vancouver gas contractor who installs and services both lines and can speak honestly to how each performs in the field.
Safety note
If you smell gas, hear a hissing sound near the water heater, or a carbon monoxide alarm sounds, leave the house immediately and call FortisBC at 1-800-663-9911 from outside before doing anything else. Do not try to relight a gas appliance yourself, and do not use the water heater again until a Technical Safety BC licensed gas fitter has cleared it.
Condensing technology is generally designed to capture more usable heat from the exhaust stream, but real-world efficiency also depends on install quality, venting, and maintenance - it's not a guarantee that plays out identically in every install regardless of those factors.
Not directly in most cases - condensing units typically use different venting material rated for lower exhaust temperatures, and existing non-condensing venting usually needs to be replaced or supplemented with a condensate drain. A technician assessment will confirm what your specific install allows.
We don't have manufacturer figures to compare here, and lifespan on either line depends far more on maintenance and water quality than on which technology it uses. Both require regular descaling to perform well long-term.
Usually yes, if you're changing from non-condensing to condensing venting, since that typically means new venting material and a condensate drain path rather than a straight swap. Ask for that scope explicitly in your assessment.
Both are part of Rinnai's current lineup as of this writing, but manufacturer lineups do shift over time - confirm current production status with your technician or Rinnai directly if that's a deciding factor for you.
We don't default to one over the other - the right choice depends on your venting situation, whether it's a swap or new install, and your household's demand, and a technician will walk through your specific home before recommending either.
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