Water Heater comparison
Tank vs Tankless Water Heater: Which Size and Type is Right for Your Home?
By the WhatSize editorial team 5 min read Standards-reviewed
The debate between tank and tankless water heaters comes down to more than preference — it's about your household size, usage patterns, energy source, and budget. This guide breaks down sizing for both types so you can make the right choice.
Tank vs Tankless: Side-by-Side
| Factor | Tank | Tankless |
|---|---|---|
| Sizing metric | Gallons (40-80 gal) | Flow rate (GPM) |
| 3-4 person household | 50 gal tank | 6-8 GPM unit |
| Upfront cost | $300 - $900 | $500 - $2,000+ |
| Installation | Simple replacement | May need gas line upgrade |
| Energy efficiency | 0.60-0.67 EF | 0.82-0.98 EF |
| Lifespan | 10-15 years | 20+ years |
| Endless hot water | No (runs out) | Yes (on-demand) |
When to choose Tank
- You have a budget under $1,000 for the unit itself
- Your household rarely runs out of hot water with your current tank
- You want a simple, proven technology with lower repair costs
- You don't have space for a gas line upgrade (for gas tankless)
When to choose Tankless
- You frequently run out of hot water with a tank
- You want energy savings of 24-34% over a tank (for gas models)
- You have the budget for higher upfront cost and potentially a gas line upgrade
- You want 20+ year lifespan and don't mind annual descaling maintenance
- You have a large household (5+ people) or high simultaneous usage
Top pick for each option
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Frequently asked questions
What GPM do I need for a tankless water heater?
For a 3-4 person home, you need a tankless unit rated for 6-8 GPM. This allows for 2-3 simultaneous uses: one shower (2.0 GPM), dishwasher (1.5 GPM), and a faucet (1.0 GPM) running at the same time.
Does a tankless water heater save money?
Gas tankless water heaters save $100+ per year for a family of four compared to a standard tank. Electric tankless savings are smaller because electricity costs more per BTU. The payback period is typically 5-10 years.
Can I replace my 50-gallon tank with a tankless?
Yes, but it's not a straightforward swap. Tankless units may require a larger gas line (3/4" instead of 1/2"), upgraded venting, and a dedicated electrical circuit. Installation can cost $1,200-3,500 in addition to the unit.
All Water Heater sizing guides
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?
- Tank vs Tankless Water Heater: Which Size Is Right?
- 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?
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