The short answer: A conventional storage-tank water heater costs less to buy and install and easily supplies several hot-water taps at once, while a tankless (demand) unit lasts roughly twice as long, saves space, and delivers continuous hot water — but costs more up front and can be flow-limited. If your household uses a modest amount of hot water and you plan to stay in the home for many years, tankless usually pays off. If you need a large volume of simultaneous hot water on a tight budget, a tank is often the better buy. And if you heat water with electricity, a third option — a heat pump (hybrid) water heater — is dramatically more efficient than either.
How the two types work
A storage-tank water heater keeps 40 to 80 gallons of water hot around the clock so it is ready when you open a tap. Because it holds a reservoir, it can serve a shower, a dishwasher, and a washing machine at the same time. The tradeoff is standby heat loss: energy spent keeping the tank hot even when no one is using water.
A tankless (or demand-type) water heater has no reservoir. When you open a hot tap, cold water flows through the unit and a gas burner or electric element heats it on the spot. Because there is no tank losing heat between uses, the U.S. Department of Energy reports that tankless models are about 8%–34% more energy efficient than storage water heaters, with the larger savings in households that use less hot water.[1]
Side-by-side comparison
| Factor | Storage tank | Tankless (demand) |
|---|
| Typical lifespan | ~8–12 years, sometimes up to 15[7] | About 20 years or more[1] |
| Energy efficiency vs. tank | Baseline (loses standby heat) | ~8%–34% more efficient[1] |
| Simultaneous hot water | Excellent (draws from stored volume) | Limited by flow rate, ~2–5 GPM[1] |
| Typical installed cost | ~$600–$3,500[7] | ~$1,400–$5,600[8] |
| Space required | Large floor footprint | Compact, wall-mounted |
| Key maintenance | Flush tank, check anode rod yearly[10] | Descale yearly (more often in hard water)[10] |
What it costs
Installed prices vary widely by fuel type, local labor, and whether your home already has the right gas line, venting, or electrical capacity. As a planning range:
- Storage tank, installed: roughly $600–$3,500, with gas and electric models overlapping across that range.[7]
- Tankless, installed: roughly $1,400–$5,600, with electric units at the lower end and natural-gas units at the upper end because they often need larger gas lines and new venting.[8] Forbes puts tankless installation alone at about $1,000–$3,500 on top of the unit.[9]
- Heat pump (hybrid), installed: roughly $1,200–$3,500 for a replacement.[7]
Operating cost is where tankless earns back some of its higher purchase price, but the gap between a gas tankless and a gas tank is often modest. One important caveat from DOE: a higher efficiency rating does not always mean a lower annual bill, especially when you are comparing different fuels — the price of gas versus electricity in your area matters as much as the equipment.[4]
Understanding the efficiency label (UEF)
Water heaters are rated by Uniform Energy Factor (UEF), the Department of Energy's standard measure of how much of the energy a unit consumes actually ends up heating your water rather than being wasted.[3] Conventional gas and electric-resistance models typically fall in the 0.6–0.95 range, while heat pump water heaters can post UEF values above 3.0 because they move existing heat instead of generating it.[3]
One catch: DOE assigns UEF within "bins" based on a unit's first-hour rating, so a UEF number is only directly comparable to other heaters in the same bin.[4] Use UEF to compare like-for-like, not to compare a small unit against a large one.
Sizing matters — especially for tankless
A storage tank is sized by its first-hour rating (how many gallons it can deliver during a busy hour), which you match to your household's peak-hour demand.[2]
A tankless unit is sized instead by flow rate (gallons per minute) at the temperature rise you need. This is where households get caught out: DOE notes that a typical gas tankless unit can produce roughly a 70°F temperature rise at about 5 gallons per minute, while an electric tankless unit manages only about 2 gallons per minute at that rise.[2] To picture the limit, a shower uses about 2.5 GPM and a kitchen faucet about 0.75 GPM, so running both at once already requires a unit rated for at least ~3.25 GPM. If you regularly run several fixtures simultaneously in a cold climate, you may need a larger gas unit or more than one tankless heater.
The third option: heat pump (hybrid) water heaters
If your home uses electricity for water heating, the biggest efficiency prize is usually not tankless at all — it is a heat pump water heater. Instead of generating heat with an element, it uses electricity to move heat from the surrounding air into the water, which makes it two to three times more energy efficient than a conventional electric-resistance unit.[5] ENERGY STAR estimates a family of four saves around $550 a year and more than $5,600 over the unit's lifetime versus a standard electric model.[6]
The catch is the installation space. A heat pump water heater needs a location that stays roughly 40°F–90°F year-round with at least about 1,000 cubic feet of surrounding air to draw heat from, so a cramped closet usually will not work.[5] A basement or utility room in a temperate climate is ideal.
Maintenance you shouldn't skip
Both types last longer with a little attention. For a tankless unit, flush and descale the heat exchanger at least once a year — and about every six months if you have hard water — to keep mineral scale from choking performance.[10] For a storage tank, check the sacrificial anode rod each year and replace it when it is heavily corroded, and flush sediment from the tank annually; the manufacturer Rheem notes that an annual anode check alone "can add years to your water heater's lifespan."[10]
A note on tax credits
The federal 25C Energy Efficient Home Improvement Credit previously covered 30% of the cost of a qualifying heat pump water heater, up to $2,000 per year. That credit expired for equipment placed in service after December 31, 2025, so it is no longer available for new 2026 installations.[11] Before you buy, it is still worth checking for current state and local utility rebates, which often exist independently of the federal program.
Which should you choose?
Choose a storage tank if you want the lowest upfront cost, you frequently run several hot-water fixtures at the same time, or your home lacks the gas-line or electrical capacity a tankless upgrade would require.
Choose tankless if you value continuous hot water and long service life, you want to reclaim the floor space, and your household's simultaneous demand fits the unit's flow rate — and you plan to stay long enough for the energy savings and 20-year lifespan to pay back the higher install cost.
Choose a heat pump (hybrid) if you heat water with electricity and have a suitable, temperate space; it usually beats both other options on operating cost.
Questions to ask your installer
- Based on my household's peak-hour demand, what capacity (gallons or GPM) do you recommend, and why?
- Does my home already have the gas line size, venting, or electrical panel capacity this unit needs — or is that an added cost?
- What is the total installed price, including permits and any code-required upgrades?
- What UEF is this specific model, and how does it compare to alternatives in the same size class?
- What maintenance will it need, and do you offer a service plan?
Frequently asked questions
Does a tankless water heater really never run out of hot water?
It provides continuous hot water as long as demand stays within its flow-rate limit. If you exceed that limit — too many fixtures at once — the water gets cooler, not endless. Size the unit to your simultaneous demand.[2]
Is tankless always more efficient?
Tankless is more efficient than a comparable tank because it avoids standby losses, but a higher efficiency rating does not guarantee a lower bill across different fuels. Local gas and electricity prices affect the real-world outcome.[4]
How long will each type last?
A storage tank commonly lasts about 8–12 years (sometimes up to 15),[7] while a tankless unit is generally rated for about 20 years or more with proper descaling.[1]