What tankless installation actually involves — and why fuel decides the bill
The sticker price of a tankless unit is the small part of what you'll pay — installation is where the money goes, and it's driven almost entirely by fuel type. A gas tankless usually needs new stainless venting (condensing units vent in cheap PVC; non-condensing need pricier Category III stainless), often a larger gas line (tankless burns far more BTU on demand than a tank), and sometimes a gas-meter upgrade — which is why a gas swap commonly runs $1,500–$3,500+ installed. An electric tankless skips the venting entirely but needs serious electrical — often multiple 40–60A double-pole breakers and a panel with the capacity to feed them, which can mean a service upgrade in an older home. The honest rule: if you're replacing a gas tank with a gas tankless, the venting + gas line dominate; if you're going electric, the panel is the gatekeeper. The tool below factors install-relevant specs — condensing venting (cheaper to vent), fuel, recirculation — into a value ranking; every slider is yours. For a full line-item breakdown see our installation cost calculator.
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.