A tank water heater costs less to buy and install. A tankless water heater costs less to run and takes far less space, but it needs a bigger upfront budget and, in many houses, upgrades to the gas line, venting or electrical service. Neither is better for every home. Your hot water habits, your existing utilities and how long you plan to stay decide the winner.
This guide compares the two on the points that change the bill: purchase and installed cost, operating cost, capacity, space, maintenance and lifespan. It also covers gas vs electric, the real downsides of tankless, and how to decide before you call a plumber.
TL;DR
- Tank heaters are cheaper upfront. Good Housekeeping puts installed cost at $900 to $1,800 for storage tanks and $1,200 to $3,500 for tankless.
- Tankless units cost less to run. Consumer Reports lists gas tankless at $195 a year against $245 for a gas tank, and electric tankless at $535 against $580.
- Tankless can be limited by flow, and retrofits often need a larger gas line, new venting or more electrical capacity.
- Gas heaters generally cost about half as much to run as electric ones, though gas models cost more to buy.
- Hard water means regular flushing for either type. Ask for a site-specific quote before you decide.
Table of Contents
- How the two heaters work
- Side-by-side comparison
- Cost: what you pay now
- Cost: what you pay over time
- Gas vs electric: the fuel decision
- Hot water capacity and speed
- Space and layout
- Maintenance and lifespan
- The real downsides of each type
- Perspective: why some plumbers are cautious about tankless
- When it is worth replacing a tank with tankless
- Book a water heater replacement in Rogers, AR
- How to compare quotes
- FAQ
- Sources
How the two heaters work
A storage tank heater holds a large volume of water and keeps it hot all day. Consumer Reports describes tanks as storing and continuously heating roughly 30 to 80 gallons. When you open a tap, hot water leaves the top of the tank and cold water enters at the bottom to be heated.
A tankless heater, also called an on-demand heater, has no reservoir. When water flows, a heat exchanger heats it as it passes through. When the tap closes, the unit stops. Because it only runs when water is moving, it avoids the standby heat loss that a tank has while it keeps water hot around the clock.
That one difference drives everything else in this comparison: a tank gives you a fixed supply that runs out and then recovers, while a tankless unit gives you a steady flow limited by how much water it can heat per minute.
Side-by-side comparison
| Factor | Tank water heater | Tankless water heater |
|---|---|---|
| Installed cost | $900 to $1,800 | $1,200 to $3,500 |
| Annual operating cost (gas) | $245 | $195 |
| Annual operating cost (electric) | $580 | $535 |
| Hot water supply | Limited to tank volume, then recovery time | Continuous, limited by flow rate |
| Space | Floor space for a large cylinder | Compact, often wall-mounted |
| Retrofit complexity | Usually a straight swap | Often needs gas, venting or electrical upgrades |
| Maintenance | Annual sediment flush, periodic T&P valve test | Periodic descaling and flushing |
| Lifespan | Shorter | Longer |
Installed cost ranges come from Good Housekeeping's water heater buying guide. Operating costs come from Consumer Reports' tank vs tankless testing. That test was published in 2019, so energy prices today will move the dollar figures, but the gap between the two types is the useful part.
Cost: what you pay now
Tankless units cost more to buy and more to install. Consumer Reports found tankless models tend to cost more up front, and the gap widens when the house needs work to support the unit.
A tank swap is usually simple. The old unit comes out, the new one goes in the same spot, and the existing gas line, vent or electrical circuit is reused. A tankless install is more involved. Good Housekeeping notes it often needs a gas line with a larger diameter, new venting, or an electrical service upgrade, such as to 200 amps.
Those extras explain why quotes for the same unit can differ by thousands. The Alliance for Residential Building Innovation advises using site-specific cost estimates in retrofits, because implementation costs vary widely with the existing home infrastructure. In plain terms: a national average tells you little. Your house tells you more.
If you want to see what an itemized quote should contain, read our breakdown of what a real tankless water heater quote includes. For tank units, our water heater replacement cost guide has a quote checklist.
Cost: what you pay over time
Running costs favor tankless. In Consumer Reports' figures, a gas tankless unit costs about $195 a year to operate and a gas tank about $245. For electric, it is about $535 for tankless and $580 for a tank.
Do the math on the gap. Gas saves about $50 a year. Electric saves about $45. Even if the tankless unit costs $1,000 more to install, that is a payback measured in decades, not years, at those figures. Consumer Reports quoted an expert who said it does not make financial sense to replace a working tank with tankless when the payback can be longer than the typical 12 to 15 year warranty.
Savings grow when you use less hot water in a day, since a tank loses heat whether you draw water or not. They shrink in a busy household that draws hot water constantly. Tankless is not a money-saving machine in most retrofits. It is a space, supply and efficiency choice that may or may not pay back.
Gas vs electric: the fuel decision
This choice often matters more than tank vs tankless.
Consumer Reports says gas water heaters generally cost about half as much to run as electric ones, though gas models cost more at purchase. The pattern holds in both types: the cheaper the fuel, the lower the yearly bill, and the higher the starting price.
What that means in practice:
- Gas tank: higher purchase price than electric, lowest running cost of the tank options. Needs a gas line and a vent.
- Electric tank: lowest purchase price, highest running cost. Needs a dedicated circuit and no vent.
- Gas tankless: best running cost, but the unit needs a gas line sized for its higher burst of demand and proper venting.
- Electric tankless: no venting, but it draws a large amount of power. Panel capacity is the question.
The practical rule: use the fuel your home already has. Switching fuel adds gas line or electrical work to the project. If you are weighing a new gas run, see our guide to gas line installation costs.
Hot water capacity and speed
A tank gives you a fixed reserve. A large household that showers back to back can run it empty, then wait for recovery. A tankless unit does not run out, but it has a ceiling on flow. Run a shower, a dishwasher and a washing machine at once, and a unit that is too small will struggle to keep temperature. Consumer Reports lists limited flow for simultaneous high demand as a known drawback.
Sizing is what separates a good tankless install from a disappointing one. Natural Resources Canada's Water Heater Guide points out that incoming water is much colder in winter, which affects how much flow a tankless unit can heat to temperature. It is a Canadian document, but the physics apply anywhere winters run cold. Northwest Arkansas winters are milder than Canadian ones, yet cold-season sizing is still the number to check, not the summer one.
There is also a delay issue. Consumer Reports notes some tankless units take longer for hot water to reach the tap, because the unit has to fire up and the pipe run still has to clear.
Space and layout
If floor space is your constraint, tankless wins. A wall-mounted unit frees a closet, a garage corner or a utility room. That matters in small homes, condos, finished basements and remodels where every square foot counts.
A tank needs a footprint, a drain pan and clearance for service. It also needs a place for the vent, if gas. If your water heater sits in a spot you are happy with, space alone does not justify the switch.
Maintenance and lifespan
Both types need upkeep. The Spruce says tankless units generally last longer but need periodic descaling and flushing, while tank heaters need an annual sediment flush and periodic testing of the temperature and pressure relief valve.
Hard water is the common thread. Consumer Reports says that in hard-water areas, a tankless heater's heat exchanger needs periodic flushing to clear mineral deposits. Skip it, and scale cuts efficiency and flow. Tanks suffer too: sediment builds at the bottom, the burner or element works harder and the tank wears out sooner.
If your water is hard, treat the water as well as the heater. A softener or whole-house system protects any water heater. See our water softener installation options and our guide to whole house filter costs.
If your current heater is not heating at all, do not shop yet. Run through five quick checks for a water heater that is not heating first. It may be a thermostat, breaker or pilot problem, not a dead unit.
The real downsides of each type
Tankless downsides
Consumer Reports lists the main ones:
- Higher purchase and installation cost.
- Possible gas line, venting or electrical upgrades.
- A delay before hot water arrives.
- Limited flow when several fixtures run at once.
- Regular maintenance in hard-water areas.
Tank downsides
- A finite supply. When it empties, you wait.
- Standby heat loss, because the water stays hot all day.
- A bigger footprint.
- A shorter life than most tankless units, and a tank failure can flood the space around it. That is why a drain pan and a leak check matter.
Perspective: why some plumbers are cautious about tankless
People ask why plumbers do not always push tankless. Our answer is practical, not ideological.
We install both. What we see on the job is that a tankless unit is only as good as the house around it. The unit may be fine, but the gas line may be too small, the vent run may not work, the panel may have no room, or the water may be hard and the owner may never flush the heat exchanger. When those pieces are not checked before the sale, the customer gets a surprise bill and a unit that underperforms.
So we start with the house. We check the gas line capacity, the electrical service, the venting and the water hardness, the same checks Consumer Reports lists before a switch. Then we size the unit to the household's peak demand, not its average. If a tank is the better fit, we say so and quote the tank. If a tankless unit will serve the home well, we quote the full scope, including upgrades, so the number you see is the number you pay.
Our view: tankless makes the most sense in new builds, major renovations, tight spaces and homes where long, continuous hot water matters and the infrastructure is ready. A straight like-for-like tank swap makes the most sense when the budget is tight, the old unit is failing and nothing else needs to change.
— Jonathan
When it is worth replacing a tank with tankless
Use these questions as a filter.
- Is your tank leaking or failing now? Then the decision is urgent. A tank swap is usually quickest and cheapest. Tankless may need parts and permits that take time.
- Is the house under renovation or new construction? This is the best moment for tankless. Gas lines, vents and circuits are easy to run while walls are open.
- Do you need floor space? If yes, tankless earns its price.
- Does the house have the capacity? Check gas line size, electrical service, venting and water hardness.
- How long will you stay? With savings near $50 a year in Consumer Reports' figures, long ownership helps. A short stay rarely pays back the extra cost.
- How many fixtures run at once? Large households with simultaneous demand need a larger unit, or two.
If you answered yes to the renovation, space and capacity questions, tankless is a strong fit. If most answers point to cost and speed, buy a quality tank.
Book a water heater replacement in Rogers, AR
We install and replace both types in Rogers and the surrounding area. Our water heater replacement and installation service covers tank units, and our tankless water heater installation and replacement covers on-demand units. Every job starts with a check of your gas, venting, electrical and water conditions, and a quote that lists the work in full. If your heater has failed and you cannot wait, use our emergency plumbing repairs line. You can also start from joco.plumbing.
How to compare quotes
Whichever type you choose, get the same details from every contractor:
- Unit brand, model, capacity or flow rate, and fuel type.
- Whether the quote includes gas line, vent, electrical, permit and haul-away work.
- Expansion tank, drain pan and shutoff valves for tank installs.
- Water hardness plan: softener, scale filter or flush schedule.
- Warranty terms for parts and labor.
- A written line for any upgrade that might be needed once work begins.
A low bid that leaves out the gas line or vent is not a low bid. It is an estimate with a gap. Ask for the scope in writing.
FAQ
Is a tankless water heater worth it?
It can be, in the right house. It is most worthwhile in a new build or renovation, in tight spaces, and where the gas or electrical service is already sized for it. In a simple replacement where upgrades are needed, the savings may not repay the extra cost within the warranty period.
What is the downside of a tankless water heater?
The main downsides are the higher purchase and installation cost, possible gas line, venting or electrical upgrades, limited flow when many fixtures run together, and a delay before hot water arrives. Hard water adds a maintenance need, since the heat exchanger must be flushed on schedule.
Is gas or electric cheaper?
Gas generally costs about half as much to run as electric, though gas models cost more to buy. If your home already has a gas line, a gas heater usually gives the lowest running cost. If it does not, the cost of adding a line should be part of the comparison.
Do tankless water heaters last longer than tanks?
Generally yes. The Spruce reports that tankless units have a longer lifespan, as long as they are descaled and flushed on schedule. Tanks need an annual sediment flush and periodic testing of the relief valve to reach their full life.
Can I replace my tank heater with a tankless one myself?
We do not recommend it. A tankless install often involves gas line sizing, venting and electrical service, which are safety work. Have a licensed plumber check the house and install the unit.
Sources
- Save Money with an Energy-Efficient Water Heater, Consumer Reports
- Tankless Water Heaters vs. Storage Tank Water Heaters, Consumer Reports
- Water Heater Buying Guide: Everything to Consider, Good Housekeeping
- Tankless vs. Tank Water Heater: What's the Difference?, The Spruce
- Strategy Guideline: Proper Water Heater Selection, Alliance for Residential Building Innovation
- Water Heater Guide, Natural Resources Canada