The essentials
- Storage tank units typically cost $300 to $480 while tankless units run $800 to $1,000 before installation.
- Tankless heaters are 24 to 34 percent more efficient in homes using 41 gallons of hot water or less per day.
- Tanks last 10 to 15 years; a well-maintained tankless unit can last 20 years or more.
- Tanks are sized by first hour rating in gallons; tankless units are sized by flow rate in gallons per minute.
- Plan a replacement before your heater fails, since most installations happen during an emergency.
When a water heater fails, you usually have to make a decision fast, often with a plumber standing in the basement waiting for an answer. The two most common choices are a conventional storage tank heater and a tankless, or on-demand, unit. They heat water differently, cost different amounts up front and over time, and place different demands on your gas line, electrical service and venting. This comparison walks through each factor so you can decide which one fits your home before an emergency forces the choice.
How Each Type Heats Water
A storage tank heater does exactly what the name suggests. It heats water with a gas burner or electric elements and holds that water at a thermostatically controlled temperature until a faucet, shower or appliance calls for it. Most residential tanks hold 30 to 80 gallons. The tradeoff is standby loss: the unit reheats water around the clock, whether or not anyone uses it.
A tankless heater warms water directly as it flows through the unit. When you turn on a hot water tap, cold water travels through a pipe into the heater, where a gas burner or electric element brings it up to temperature. There is no stored supply to deplete, so a tankless unit can deliver hot water continuously for as long as the shower runs. By definition, these units hold almost no water, no more than one gallon for every 4,000 Btu per hour of input. The catch is flow rate: the unit can only heat so many gallons per minute, which we cover in the sizing section below.
Upfront and Installation Costs Compared
Tankless units cost more to buy and more to install. Published price ranges put a standard storage tank water heater at $300 to $480 for the unit itself, while tankless heaters range from $800 to $1,000. Installation widens the gap. One national cost guide puts the average water heater installation between $1,600 and $5,800 overall, with electric tank installs running $920 to $1,177 and gas tank installs averaging around $2,607. Tankless installations average roughly $2,791 to $3,236 per heater, largely because gas models often need a new electrical outlet, larger gas piping and an upgraded ventilation system.
Here is the comparison at a glance:
| Factor | Storage Tank | Tankless |
|---|---|---|
| Typical unit price | $300 to $480 | $800 to $1,000 |
| Typical installed cost | $920 to $1,177 (electric), about $2,607 (gas) | $2,791 to $3,236 |
| Typical lifespan | 10 to 15 years | 20 years or more with proper maintenance |
| Capacity measure | First hour rating, in gallons | Flow rate, in gallons per minute |
| Hot water supply | Can run out until the tank reheats | Continuous, but limited by flow rate |
| Best fit | Budget replacements and high simultaneous demand | Long-term savings and tight spaces |
A like-for-like tank swap is usually the cheapest job because the gas line, venting and plumbing stay where they are. Any switch of fuel type or technology adds cost.
Energy Use and Monthly Bills
Water heating is the second largest energy expense in most homes. The average household spends $400 to $600 a year heating water, which works out to 14 to 18 percent of utility bills. Both tankless and high-efficiency tank options attack that number, just from different directions.
Because a tankless unit only heats water on demand, it skips the standby losses entirely. Federal energy data shows tankless heaters are 24 to 34 percent more efficient than tank models in homes that use 41 gallons or less of hot water per day, and 8 to 14 percent more efficient in homes using around 86 gallons a day. A household that installs multiple tankless units to cover simultaneous demand can reach 27 to 50 percent in energy savings. Fuel matters too: gas water heaters generally cost about half as much to run as electric ones, though gas models cost more at purchase.
One more option belongs in the conversation. Heat pump water heaters, which move heat from the surrounding air into the tank instead of generating heat directly, use about one-quarter of the energy of a standard electric model. An ENERGY STAR certified heat pump unit can save a household of four roughly $600 a year on electric bills, with the upfront premium paid back in about three years. For habits that cut costs regardless of which unit you own, see 7 Ways to Lower Your Water Heating Bill.
Lifespan, Warranties and Maintenance
Longevity is where tankless units earn back some of their higher price. A conventional tank typically lasts 10 to 15 years, which means most homeowners replace one more than once while living in a house. A tankless unit that receives proper maintenance can last 20 years or longer, and because its parts are easy to find and replace, service can extend the life well beyond that.
Maintenance differs between the two. A tank needs periodic flushing to control sediment, an annual check of the temperature-pressure relief valve and occasional anode rod service. A tankless unit needs periodic descaling, especially in hard water areas, to keep mineral buildup from clogging the heat exchanger. If you already own a tank, our water heater care timeline lays out what to do each month and each year to reach the upper end of that 10 to 15 year range.
Warranty terms vary by model and manufacturer, so read them before you buy and note what maintenance the warranty requires you to perform.
Sizing: First Hour Rating vs. Flow Rate
The two types are measured in different units, and mixing them up leads to undersized installations.
A storage tank is sized by its first hour rating, or FHR: the maximum volume of hot water, in gallons, the heater can supply in an hour that starts with the tank fully heated. A household that draws a lot of hot water in the morning needs an FHR that covers that combined demand.
A tankless unit is sized by gallons per minute, or GPM, the flow of hot water it can sustain at a given temperature rise. Federal energy data shows tankless heaters typically deliver 2 to 5 gallons per minute, with gas-fired models producing higher flow rates than electric ones. That limit matters in real life. If someone is showering while the dishwasher runs, even a gas-fired tankless unit can struggle to keep up. Possible fixes include installing multiple tankless units connected in parallel, or dedicating separate small units to high-demand appliances. An experienced plumber can estimate your household’s simultaneous hot water demand and confirm the right GPM before you buy.
Gas, Electric and Venting Requirements
Fuel type shapes the installation as much as the technology. Consumer gas storage heaters operate at 75,000 Btu per hour or less, while gas tankless units can draw up to 200,000 Btu per hour, which is why a tankless conversion often requires larger gas piping than the old tank used. Electric tankless units can draw up to 12 kilowatts, sometimes forcing an upgrade to your electrical service. Electric tanks, by contrast, need no venting at all and are often the simplest and cheapest to install where electrical capacity exists.
Gas units, whether tank or tankless, burn fuel inside the home and must vent combustion gases safely outdoors. The installer should confirm how those gases will be vented and whether your existing gas line can supply the new unit. Because gas appliances are one potential indoor source of carbon monoxide, working alarms matter; see our guide to smoke and carbon monoxide alarms for placement and testing. Switching fuels, adding gas lines or upgrading electrical service all require permits and a licensed professional.
Safety first
Most water heater replacements happen during an emergency, which leaves you little time to compare options or negotiate price. If your tank is more than a decade old, start researching now so you can choose a unit on your schedule, not the tank’s.
Which One Fits Your Household
Neither type wins across the board. The better choice depends on your budget, your usage patterns and what your home’s utilities can support.
A storage tank makes sense if you:
- Need a fast, affordable like-for-like replacement
- Often run the shower, dishwasher and washer at the same time
- Prefer the lowest purchase price and simplest installation
- May move within a few years and want the shorter payback horizon
A tankless unit makes sense if you:
- Plan to stay in the home long enough to recover the higher upfront cost
- Use modest amounts of hot water, where the efficiency gains are largest
- Want continuous hot water for long showers or back-to-back baths
- Are short on space, since a tankless unit is roughly the size of a suitcase
- Are building new or doing a major remodel, when running the right gas, electric and venting infrastructure is easiest
Before you commit, get written estimates from a licensed installer for both options. The installer should confirm the correct first hour rating or GPM for your household, check whether your gas line and electrical service can support the unit, and explain the venting plan. Check for rebates on certified high-efficiency models in your area, and keep your current heater running well until you are ready; the care timeline above will help with that. A planned replacement costs less, goes smoother and ends with a unit you actually chose.
Related guides
- A Timeline for Water Heater Care: monthly and yearly tasks that stretch a tank’s lifespan toward the top of its range.
- 7 Ways to Lower Your Water Heating Bill: settings and habits that cut costs no matter which heater you own.
- Smoke and Carbon Monoxide Alarms: Where to Put Them and How to Test Them: essential backup if you keep a gas-burning heater in the house.
Common questions
Is a tankless water heater cheaper to run than a tank?
Usually, yes. Tankless units avoid the standby losses of keeping a tank hot, and studies report 8 to 34 percent energy savings depending on how much hot water your household uses each day.
Can a tankless water heater run out of hot water?
It never runs out the way a tank does, but its flow rate is limited, typically 2 to 5 gallons per minute. Running a shower and dishwasher at the same time can exceed that, so some homes install two units.
Do I need a professional to install either type?
Yes. Water heaters involve gas lines, high-amperage electrical circuits, venting and plumbing that must meet code. A licensed plumber or contractor should handle the installation.
How long does each type last?
A storage tank water heater typically lasts 10 to 15 years. A tankless unit that gets proper maintenance can last 20 years or longer, and replaceable parts can extend its life further.
This guide is general information, not professional advice. Follow the manufacturer’s instructions and your local building codes, and hire a licensed professional for electrical, gas, structural or roofing work.