Water Heater comparison
Tankless vs Tank Water Heater: Size & Cost Comparison
By the WhatSize editorial team 5 min read Standards-reviewed
The fundamental question for any water heater upgrade is tank vs tankless. The trade-offs span upfront cost, operating cost, lifespan, footprint, and recovery capability. Tank heaters are sized by FHR (First Hour Rating) per DOE 10 CFR 430 — measured in gallons delivered in the first hour. Tankless units are sized by GPM at 67°F rise per the same DOE standard — flow rate at the federal test condition.
For 1–2 person households, tank is cheaper upfront. For 3+ person households, tankless saves 24–34% on water heating energy over a 20+ year lifespan with breakeven at 6–10 years.
Tank Water Heater vs Tankless Water Heater: Side-by-Side
| Factor | Tank Water Heater | Tankless Water Heater |
|---|---|---|
| Sizing method | FHR (First Hour Rating) in gallons | GPM at 67°F rise |
| First cost (installed) | $800–$1,500 (gas), $400–$900 (electric) | $1,500–$3,500 (gas), $800–$2,000 (electric) |
| Operating cost / yr | $275 (gas), $400–$600 (electric) | $250 (gas), $600 (electric) |
| Lifespan | 10–15 years | 20+ years |
| Energy efficiency | UEF ~0.60–0.92 | UEF 0.85–0.98 (gas), UEF ~0.98 (electric) |
| Hot water supply | Limited to tank capacity | Endless (GPM-limited) |
| Footprint | Floor space 4–8 sq ft | Wall-mounted, near zero floor space |
| Install complexity | Simpler (existing connections) | Gas line upgrade, venting, condensate drain |
When to choose Tank Water Heater
When to choose a tank water heater
- You have 1–2 people in the household — operating cost difference is small
- Budget is tight — $800–$1,500 installed vs $1,500–$3,500
- You want simpler installation with no gas line or venting upgrades
- You have limited wall space for a tankless unit and venting
When to choose Tankless Water Heater
When to choose a tankless water heater
- You have 3+ people and need endless hot water for multiple simultaneous showers
- You want to save 24–34% on water heating energy (DOE) over the 20+ year lifespan
- Floor space is limited — wall-mount saves 4–8 sq ft
- You're in for the long term — breakeven vs tank at 6–10 years
- You have an existing natural gas line (or can upgrade) — gas tankless dominates the 3+ person segment
Frequently asked questions
Is tankless really better than tank?
For 3+ person households, yes. Tankless saves 24–34% on water heating energy, lasts 20+ years vs 10–15 for tank, and provides endless hot water. Per DOE Energy Saver, the energy savings are real but smaller in high-use homes (8–14%). For 1–2 person households, tank is more cost-effective upfront.
Why is tankless more expensive than tank?
Tank heaters are cheaper upfront ($800–$1,500) due to simpler heat-exchanger technology. Tankless has a complex heat exchanger + control electronics + condensing tech = $1,500–$3,500. Installation also costs more: gas line upgrade ($300–$800), venting ($300–$800), condensate drain ($150–$400). Energy savings + longer lifespan offset the higher upfront cost over 6–10 years.
Can I convert from tank to tankless?
Yes, but requires: (1) gas line upgrade (1/2" to 3/4" for 199k+ BTU); (2) venting installation (direct-vent or power-vent); (3) condensate drain for high-efficiency units; (4) electrical upgrade if adding a recirculation pump. Budget $2,500–$5,000 for full gas conversion, $1,500–$3,000 for electric conversion.
How much does a tankless water heater cost?
Gas tankless: $1,000–$2,500 for the unit, $1,500–$3,500 installed. Electric tankless: $500–$1,500 for the unit, $800–$2,000 installed. Installation costs vary by region and existing infrastructure.
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- Electric Tankless Water Heater Sizing Guide
- Gas Tankless Water Heater Sizing Guide
- Electric vs Gas Tankless Water Heater: Which Size & Type?
- Heat Pump vs Tankless Water Heater: Size & Efficiency
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- Propane Tankless Water Heater Sizing Guide
- RV Tankless Water Heater Sizing Guide
- Tankless Water Heater Installation Cost Guide
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