Water heater sizing Last reviewed June 30, 2026
Tank vs Tankless Water Heater: Which Size Is Right?
By the WhatSize editorial team 4 min read Standards-reviewed
Choose a tank water heater for lower upfront cost ($400-900) and simpler installation. Choose tankless ($500-2,300) for unlimited hot water, longer lifespan (15-20 years), and 20-30% energy savings.
Tank vs Tankless: The Key Differences
The fundamental difference is how each type stores and delivers hot water. A tank water heater stores 30-80 gallons of pre-heated water and reheats it as needed. A tankless unit heats water on demand — it has no storage tank and provides continuous hot water as long as the flow rate doesn't exceed its capacity.
For sizing: tank units are sized by gallon capacity (how much they can store). Tankless units are sized by GPM (how much they can heat per minute). A 7.5 GPM tankless unit can handle 2-3 showers simultaneously — equivalent to a 60-80 gallon tank.
Which is right for you depends on household size, fuel type (gas vs electric), climate (incoming water temperature affects GPM), and budget.
Top picks for this size
These Amazon-available picks meet the calculated spec. For region-specific or licensed contractor-installed options, consult a local professional. See our Disclaimers.
Tank vs Tankless Decision Guide
- Choose tank (40-80 gal, $400-900) if: lower upfront cost matters, easier installation, existing compatible electrical/gas hookup, household size consistent
- Choose tankless (4.3-7.5+ GPM, $500-2,300) if: energy savings matter (20-30% vs tank), unlimited hot water desired, longer lifespan important, you have natural gas available
- Hybrid tank: Best of both worlds — Rheem 50 Gal Hybrid ($1,099) uses 60% less electricity than standard tank
Frequently asked questions
Tank vs tankless water heater — which is better?
Yes, but it requires significant modifications. Tankless units need larger gas lines (for gas models), 220V electrical circuits (for electric models), and upgraded venting. Budget $1,000-2,000 for conversion in addition to the unit cost.
Do tankless water heaters save enough money to justify the cost?
Tankless units save $80-150 per year in energy costs compared to standard tanks. At a $800-1,000 premium, it takes 6-10 years to break even — about halfway through the unit's 20-year lifespan. If you stay in your home long-term, tankless pays off.
You might also need
More water heater sizing guides
- What Size Water Heater for a 1-2 Person Household?
- What Size Water Heater for a 3-4 Person Household?
- What Size Water Heater for a Family of 5?
- What Size Water Heater for Electric vs Gas Homes?
- Water Heater FHR Chart: First Hour Rating by Household Size
- Tankless Water Heater GPM Chart by Household Size
- Water Heater UEF Rating Explained: Energy Factor vs FHR Chart
- What Size Water Heater for a 2-Bathroom House?
- 40 vs 50 Gallon Water Heater: Which Size Do You Need?
Still choosing between sizes? Compare: tank vs tankless