Tankless repair: when to fix it, when to walk away
Most tankless "repairs" fall into a few buckets, and the right call is usually decided by age, warranty, and the specific fault — not the repair quote alone. Scale / limescale is the number-one killer: hard water deposits choke the heat exchanger and throw error codes long before the unit truly fails — an annual descaling flush ($100–200, or DIY) fixes or prevents it, and is almost always worth doing before you condemn a unit. Ignition / flame-sensor faults, fan or flow-sensor errors, and igniter replacements are typically $150–500 parts-plus-labor and worth it on a unit under ~8 years or still in heat-exchanger warranty (the HX is the expensive part — if it's covered, repair almost always wins). The walk-away signal is a cracked or leaking heat exchanger on an out-of-warranty unit: that repair runs $500–1,000+ and you're sinking it into a unit near end-of-life. Rule of thumb: if the repair is more than half the cost of a new unit and the heater is past its warranty, replace. If you land on replace, the tool above is already weighted toward efficiency and running cost so you can pick the best-value swap — every slider is yours.
What about installation cost?
Sticker price is only half the story — condensing units need special venting, electric units may need a panel upgrade. The tool ranks on unit value; use the fuel filter to compare within an install type (all-gas vs all-electric) so you're not comparing a cheap electric against a gas unit that costs $1,500 to vent. (A dedicated installation-cost calculator — the highest-demand tankless search — is live.)
Condensing vs non-condensing: the choice that drives both your bill and your install
This is the first real fork. A non-condensing unit (e.g. the Rinnai V75iN, ~0.81 UEF) is cheaper up front (~$780) but vents hot exhaust through expensive stainless-steel or Category III venting and wastes more heat. A condensing unit (Navien NPE, Rinnai RX, Rheem Prestige — 0.93–0.98 UEF) captures a second pass of heat from the exhaust, running cool enough to vent through cheap PVC and cutting gas use meaningfully. Rule of thumb: condensing costs $300–600 more for the unit but is usually cheaper to vent and pays back the difference in gas savings within a few years — especially if you run a lot of hot water. The tool's UEF axis is where this shows up; sort by it to see the efficiency spread directly.
Gas vs electric tankless: which one fits your house
The honest limiter on electric tankless isn't efficiency — electric units hit ~0.99 UEF — it's flow in cold climates and your electrical panel. The best electric units here (Stiebel Eltron Tempra 29, Rheem RTEX-27) top out around 2.9–3.1 GPM at a 70° rise and can demand 100+ amps of dedicated service, often forcing a panel upgrade. That's fine for a warm climate, a point-of-use application, or a small household — and electric wins on up-front price ($430–850) and needs no venting at all. Gas (natural gas or propane) is what a cold-climate whole-house family wants: 4.5–5.7 GPM at rise, no panel upgrade, but it needs a gas line and venting. Use the fuel filter above to compare like-for-like instead of pricing a $430 electric against a $1,500 gas unit that solves a different problem.
Why we don't just name a winner
"Best tankless" depends entirely on your fuel, climate and household size. A cold-climate family cares about flow; a bill-watcher cares about UEF; a landlord cares about warranty. One name buries that — the Value Score keeps it in your hands, formula in the open right above. (Sizing for a specific household? See our tankless sizing for a family of 4 walkthrough.)
The specs, briefly
UEF = efficiency, how much energy reaches the water (higher = lower bills). Flow @ 70° rise = real cold-weather simultaneous-shower capacity. HX warranty = years on the heat exchanger, the part that fails. Recirculation = instant hot water at the tap (built-in pump only — "recirc-capable" without a factory pump doesn't count here). Min-flow = how little flow fires it (low = no cold-water sandwich).
Specs verified Aug 2026 against manufacturer spec sheets + ENERGY STAR product finder. Prices are approximate street prices (unit only, not installed) pending live-retailer verification. Some links may be affiliate; that never changes the Value Score — the math runs on published specs, not payouts.