Tankless gives endless hot water, lasts ~20 years, and is 8–34% more efficient (the higher figure only for low-use homes, per DOE) — but costs roughly double upfront and often needs gas-line, venting, or major electrical upgrades. Tank is cheaper to buy and install, simpler, and better for short simultaneous bursts, but lasts ~8–15 years and loses standby heat. If you keep running out of hot water, tankless solves it; if your tank is just old, a right-sized tank is the cheaper fix. One 2026 note: the federal 25C tax credit for water heaters expired December 31, 2025.
The two types are sized completely differently, which is why one calculator can't do both. Size a tank by First Hour Rating and a tankless by GPM and temperature rise. This guide compares everything else — cost, efficiency, lifespan, and the catches nobody mentions until install day.
⚖️ Tank vs. Tankless at a Glance
Head to Head
| Factor | Storage Tank | Tankless |
|---|---|---|
| Installed cost | Lower | ~75–100% higher |
| Lifespan | ~8–15 years | ~15–20+ years |
| Hot water | Finite (tank volume), then recovery | Endless, but flow-rate (GPM) limited |
| Efficiency (vs tank) | Baseline; standby loss | 8–34% better (usage-dependent) |
| Sizing basis | First Hour Rating (gallons) | GPM at temperature rise |
| Space | Bulky floor unit | Wall-mounted, compact |
Directional comparison — the right pick depends on your usage pattern, fuel, and existing infrastructure.
💵 Upfront Cost & the Hidden Adders
The sticker gap is real but it's the install adders that decide the true cost of a tankless conversion:
Typical Installed Cost Ranges (2026)
| Type | Installed range |
|---|---|
| Gas storage tank (50-gal) | $1,700–$3,200 |
| Gas tankless | $3,000–$6,500 |
| Heat pump water heater (unit only) | $1,500–$3,000+ |
Prices last reviewed July 2026. Water-heater and install costs vary widely by fuel, venting, gas-line and electrical work, and region — treat these as wide relative ranges, not quotes, and get itemized local bids.
The adders that catch people converting tank → tankless:
- Gas line upsizing — a tankless fires at 150,000–199,000 BTU/hr and often needs a ¾" gas line the old tank never required.
- Venting — Category III stainless or PVC/concentric venting, not the old atmospheric flue.
- Electrical service upgrade — for electric tankless, frequently the biggest cost of all (see below).
- Condensate drain for condensing units, and water treatment if you have hard water (tankless heat exchangers scale up).
🔋 Efficiency & the Honest Payback
The DOE figure is precise and usage-dependent — not a flat number: tankless heaters are 24–34% more efficient for homes using ≤41 gallons/day, but only 8–14% more efficient for high-use homes around 86 gallons/day. The efficiency comes from eliminating standby loss (a tank reheats itself around the clock whether you use it or not).
On operating cost that's roughly $44–$108 a year saved (electric vs gas). Do the honest math: because a tankless conversion costs meaningfully more upfront, simple payback commonly runs 6 to 20+ years — and for a low-use household it can exceed the unit's own lifespan. Buy tankless for the endless hot water and the 20-year life, not as a money-saver, unless your usage and fuel prices genuinely pencil out.
⚡ The Electric Tankless Catch
If you don't have gas, electric tankless looks appealing — until you see the electrical demand. Whole-home electric tankless units draw 54 to 150 amps across multiple double-pole breakers:
- A Stiebel Eltron Tempra 36 draws 3 × 50 A (36 kW). An EcoSmart ECO 27 or Rheem RTEX-24 pulls 112–150 A across three or four circuits.
- Even a mid-size Tempra 20 needs 80 A (2 × 40 A); a Tempra 15 needs 60 A.
- A home on a 100-amp service almost certainly needs a 200-amp upgrade before a whole-home electric tankless is even possible.
🏦 Rebates & Tax Credits in 2026
This changed sharply, so ignore older advice:
- The federal 25C tax credit expired December 31, 2025. Under the One Big Beautiful Bill Act (signed July 2025), there is no federal tax credit for water-heating equipment placed in service on or after January 1, 2026. Equipment placed in service by the end of 2025 can still be claimed on the 2025 return.
- HEEHRA/HEAR rebates are still active in 2026 in a growing number of states — up to $1,750 for a heat pump water heater, within a $14,000 household cap. But they're income-qualified (full amount only below 80% of area median income; nothing above 150%) and funding is limited — California's single-family rebates were fully reserved as of February 2026.
- State and utility rebates vary widely and change fast. Check your state energy office and utility before assuming any incentive.
Incentive programs change frequently — verify current status with your state energy office and utility, not a blog, before you buy.
🎯 Which One Should You Buy?
- You keep running out of hot water → tankless (endless supply is its whole point).
- Your tank just died and budget is tight → a right-sized replacement tank is cheaper and simpler.
- You have gas and stay put 15+ years → gas tankless's longer life and efficiency have time to matter.
- You're all-electric → price a heat pump water heater (best efficiency by far) before electric tankless, which may force a service upgrade.
- Big simultaneous demand (several showers at once) → a large tank or a properly sized tankless; don't undersize either.
Estimate your Water Heater Size materials
Free water heater size calculator using the DOE first-hour-rating method — count your busiest hour's hot-water uses and get the FHR to shop for.
Estimate with the Water Heater Size Calculator →