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Why Plumbers Hesitate on Tankless Water Heaters

Why do plumbers not recommend tankless water heaters?

Plumbers often don’t “recommend against” tankless water heaters across the board—many install them every day. The hesitation usually comes from a few practical headaches that show up in real homes: higher upfront costs, installation complexity, maintenance needs, and performance that depends heavily on proper sizing and water quality.

1) Upfront price and installation can be steep

Tankless units typically cost more than standard tank heaters, and the install can require extras like new gas lines, upgraded venting, electrical changes, or condensation drainage (for condensing models). If a home’s utilities weren’t designed for high-demand on-demand heating, a plumber may steer customers toward a simpler tank replacement to avoid surprises.

2) Flow rate limits can feel like “not enough hot water”

A tankless heater doesn’t store hot water—it must heat it as it flows. If multiple showers, appliances, or fixtures run at once, a unit that’s undersized (or faced with very cold incoming water) may not keep up. That can lead to fluctuating temperatures or reduced flow, which homeowners often blame on the heater rather than the sizing.

3) Maintenance matters more than many homeowners expect

Tankless heaters commonly need periodic descaling to prevent mineral buildup, especially in hard-water areas. Skipping maintenance can reduce efficiency, cause noise, trigger error codes, and shorten lifespan. Plumbers know that many people won’t keep up with it—so they may recommend a tank model that’s more forgiving.

4) Retrofitting can expose “hidden” compatibility issues

Older homes may need gas supply upgrades, larger venting pathways, or electrical changes. Some installs also require careful placement to meet clearance and code rules. When the project scope grows, plumbers may prefer a tank heater as the lower-risk option.

If you’re considering a propane indoor model and want help matching flow rate to your household, see this detailed guide: 7.4 GPM Indoor Propane Tankless Water Heater Instant Hot Water Guide.

FAQ

Do tankless water heaters work well with hard water?

They can, but hard water increases scale buildup, so regular flushing/descaling and a water softener (or scale-reduction system) may be needed to maintain performance and reliability.