When your water heater starts showing its age, the replacement conversation usually turns into one question: stick with another tank, or finally make the switch to tankless?
For Southeastern Wisconsin homeowners comparing a tankless vs tank water heater, the short answer is that tankless usually costs more up front and less to run, while a conventional tank costs less up front and wears out sooner. A like-for-like tank replacement often lands around $1,500 to $3,000 installed, while converting from a tank to a gas tankless system commonly runs $3,500 to $7,000 or more once gas, venting, and plumbing changes are included.
Whether tankless actually saves more long-term depends on how much hot water your household uses, what your existing setup looks like, and how long you plan to stay in the home.
Here’s how the numbers tend to shake out.
For budgeting purposes, most water heater projects fall into one of these categories:
| Project Type | Estimated Install Cost | What Can Affect the Price |
|---|---|---|
| Gas tank replacement (40–50 gal.) | $1,500–3,000 | Tank size, efficiency rating, venting condition, code updates, haul-away |
| Electric tank replacement (40–50 gal.) | $1,200–2,500 | Tank size, electrical condition, accessibility |
| Tankless replacing an existing tankless | $2,500–4,500 | Unit capacity, condensing vs. non-condensing, reusable venting and gas line |
| Tank-to-tankless conversion (gas) | $3,500–7,000+ | Gas line upsizing, new venting, condensate drain, electrical outlet, wall mounting |
| Whole-home electric tankless | $2,000–5,500+ | Amperage required, panel capacity, possible electrical service upgrade |
These are planning ranges, not flat-rate quotes. The biggest swing usually isn’t the unit itself – it’s how much of your existing gas, venting, and water piping can be reused.
That’s why a tankless quote for one home can be double the quote for the house down the street.
Upfront price is only part of the picture. Several factors decide which system comes out ahead over 15 or 20 years.
A tank water heater keeps 40 or 50 gallons of water hot around the clock, even when nobody is using it. That standby heat loss is where tankless units gain their advantage – they only heat water when a tap is open.
According to the U.S. Department of Energy, tankless (demand) water heaters can be roughly 24% to 34% more energy efficient than storage tanks in homes that use about 41 gallons of hot water or less per day, and around 8% to 14% more efficient in homes that use much more, around 86 gallons per day.
In other words, the savings are real, but they’re a percentage of your water heating bill, not your whole utility bill. For many households, that works out to a modest annual savings rather than a dramatic one.
This is where tankless systems often make up ground. A conventional tank water heater typically lasts around 8 to 12 years. A well-maintained tankless unit can often last 20 years or more.
Over a 20-year period, a homeowner with a tank may pay for two installations, while a homeowner with tankless may pay for one.
Both systems need care. Tanks benefit from periodic flushing to clear sediment, and their anode rods eventually need replacement. Tankless units need regular descaling – typically once a year, sometimes more often with hard water – to protect the heat exchanger.
Skipping tankless maintenance is one of the fastest ways to lose the long-term savings you paid for.
Many gas tankless units need significantly more gas input than a standard tank while they’re running. If your gas line or meter wasn’t sized for that demand, the line may need to be upgraded.
Venting changes too. Many high-efficiency tankless units use dedicated PVC venting and need a condensate drain, which means your old flue may not be reusable. Most gas tankless units also need a nearby electrical outlet, and whole-home electric tankless models can require substantial electrical capacity.
These conversion costs are usually a one-time expense, but they’re the main reason a tankless project costs more the first time.
A few regional factors are worth building into your decision.
A properly sized system should reflect how your home uses water on the coldest day of the year, not the average one.
Consider a representative situation we commonly see.
A family of four in Franklin has a 12-year-old, 50-gallon gas tank in the basement. It still works, but the burner is getting noisy and the family occasionally runs out of hot water after back-to-back showers. They ask whether they should replace it with another tank or go tankless.
A like-for-like tank might cost around $2,000 installed, with another replacement likely needed in 10 to 12 years. A tankless conversion might cost around $5,000 because the gas line needs to be upsized and new venting installed, but the unit could last 20 years and trim their water heating costs every month.
Over 20 years, the gap between those two paths can narrow considerably once you account for a second tank purchase and lower energy use. For a household that plans to stay put, uses a lot of hot water, and wants endless hot water for back-to-back showers, tankless may be the better long-term fit. For a household planning to sell in a few years, a new tank is often the more practical choice.
That’s the point: neither option is automatically cheaper. It depends on the home and the household.
Incentives can change the math, but they change often. The federal energy efficiency tax credit that previously applied to many qualifying water heaters ended for equipment placed in service after 2025, so don’t count on a federal credit for a 2026 installation without confirming with a tax professional.
Wisconsin’s Focus on Energy program and local utilities periodically offer rebates on qualifying high-efficiency equipment. It’s worth checking current offers before you buy, since eligibility depends on the specific model and installation.
Some water heater problems can wait for a planned replacement. Others shouldn’t.
Call a professional if you notice:
A tankless conversion in particular isn’t a DIY project. It typically involves gas piping, venting, electrical, and permit and inspection requirements that vary by municipality. A licensed plumber can confirm what your home needs and handle the work to code.
In the tankless vs tank water heater debate, tankless often saves more over the long run for households that use a lot of hot water, plan to stay in their home 10 years or longer, and keep up with annual maintenance. A new tank often makes more financial sense when the budget is tight, the existing setup is in good shape, or you may move in the next few years.
The only reliable way to compare the two for your home is to look at your existing gas, venting, and water lines and price both options side by side.
Dr. Plumber II provides water heater services – including tank and tankless installation, replacement, repair, and maintenance – throughout Oak Creek, Franklin, South Milwaukee, Cudahy, Greenfield, Greendale, Muskego, Caledonia, and the surrounding Southeastern Wisconsin communities. Our licensed, bonded, and insured plumbers can inspect your current system, explain the real cost of each option, and recommend the setup that fits your home and your budget.
Don’t wait for a cold shower – or a flooded basement – to make the decision for you.
Thinking about tankless or ready to replace your tank? Call Dr. Plumber II at (414) 698-4528 to schedule a service call or request a water heater estimate.