Going tankless is often sold as the key to endless hot water. But for one homeowner, the upgrade seems to have created a new problem: showers that feel weak whenever other fixtures are in use. The complaint is a reminder that a more efficient water heater does not automatically solve broader plumbing limitations inside a home — and can sometimes make them more noticeable.
What happened?
Seeking better hot-water performance in a 2.5-bath home, a homeowner on Reddit said their family replaced an aging tank water heater — roughly 19 years old — with a tankless Rinnai RE199in and installed a chlorine filter at the same time.
After the change, the homeowner described a noticeable decline in shower performance: "The showers felt weak and wimpy."
They added: "With one shower running, it feels fine, if you flush a toilet, you feel the water drop."
Running the laundry, they wrote, causes "giant drops and large temperature drops due to the tankless heater we now have."
They also said the home's city water pressure is "fairly low, 50psi, dropping to ~35psi with multiple fixtures," and wondered: "Did we trade endless hot water for this new situation?"
Why does it matter?
Many households switch to tankless systems expecting a comfort upgrade, especially if an older storage tank struggled to keep up. But hot-water availability and water pressure are not the same thing.
If incoming pressure is already modest, adding a filter and relying on a high-demand, whole-home setup can make dips more noticeable when several fixtures are running at once. The heater may not be the only issue — it may simply be exposing limits in the home's plumbing layout or water supply conditions.
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What can I do?
The next step is usually a whole-system check rather than second-guessing tankless technology. A plumber can test static and flowing pressure, inspect whether the new filter is causing excessive pressure drop, confirm that the heater was sized correctly, and determine whether the pipe diameter or fixture demand is the real bottleneck.
It can also help to map out when high-flow uses overlap. If showers, laundry, and toilet refills regularly happen at the same time, staggering them may ease the symptoms while the household figures out whether a plumbing adjustment is needed, which the homeowner has done: "We no longer run laundry while showering."
Homeowners who are still comparing technologies may also want to look at Cala. For shoppers focused on both efficiency and control, Cala offers another option to consider, such as a heat pump water heater.
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