Hot water is one of those things nobody thinks about until it's gone. The shower runs cold on a January morning in Oak Forest, or the tank starts rumbling in a Schaumburg basement, and suddenly the water heater is the most important appliance in the house.
If you're facing a replacement, the choice usually comes down to a traditional storage tank or a tankless (demand-type) system. This guide covers both, plus the regional wrinkles: hard water, basement installs, busy-household demand, permits, and whether you plan to stay or sell.
24–34%: the energy efficiency advantage of tankless over storage tank water heaters for homes using 41 gallons of hot water or less per day, according to the U.S. Department of Energy.
How each type works
Standard storage tank
A tank stores hot water, usually 40 or 50 gallons for a typical family home, and keeps it at temperature around the clock. When you open a tap, hot water leaves the top and cold water refills the bottom, and the burner or element kicks back on.
The downside is standby heat loss: it uses energy to keep water hot even when nobody's using it. The upside is simplicity. Tanks are predictable, familiar to plumbers and less expensive to install. More on the mechanics: how a water heater works.
Tankless (demand-type)
A tankless water heater doesn't store water. When you open a hot tap, water flows through a heat exchanger where a gas burner or electric element heats it on the fly. When the tap closes, the burner shuts off.
With no stored water losing heat, standby losses drop to near zero. The tradeoff is flow rate. A single gas unit typically delivers 2 to 5 gallons per minute, enough for one shower plus one other fixture. Push past that and it can't keep up.
Key differences at a glance
| Item | Standard tank | Tankless |
|---|---|---|
| Typical lifespan | 10–15 years | 20+ years |
| Hot water supply | Limited to what's stored | Continuous, up to its flow rate |
| Flow limit | Tank size and first-hour rating | About 2–5 GPM per gas unit |
| Standby heat loss | Yes | Near zero |
| Installed cost | Lower | Higher |
| Space | Floor space | Wall-mounted |
Lifespan figures come from the U.S. Department of Energy and assume proper maintenance. A neglected tank may fail in 7 or 8 years, and a tankless unit that skips annual descaling can lose years off its life.
Rule of thumb: a tankless unit usually outlasts one and a half to two storage tanks. If you plan to stay 15+ years, the math starts tilting toward tankless before energy savings even enter the picture.
Sizing for a Chicago home
Picking the right capacity matters as much as picking the type. A well-sized tank that gets used hard beats an undersized tankless unit struggling to keep up, and an oversized tankless unit costs more without a real benefit.
Sizing a storage tank
Focus on the First Hour Rating (FHR), how much hot water the unit delivers in its busiest hour, not just what it stores. A 50-gallon tank with a high FHR can outperform a 65-gallon tank with a low one.
| Household | Rough starting point |
|---|---|
| 1–2 people | 40 gallons |
| 3–4 people | 50 gallons |
| 5+ people, or a soaking tub | 65–75 gallons |
Sizing a tankless unit
Add up the gallons per minute of every fixture you might run at once during your busiest moment, usually a weekday morning. Then size up from there.
| Fixture | Typical flow |
|---|---|
| Low-flow shower | About 2 GPM |
| Bathroom faucet | 1–1.5 GPM |
| Kitchen faucet | 1.5–2 GPM |
| Dishwasher or washer (hot fill) | 1.5–2.5 GPM |
The Chicago wrinkle is winter inlet temperature. Tankless ratings are quoted at a set temperature rise, often 70°F. When January water comes in at 40°F and you want 120°F, that's an 80°F rise, and the unit's effective flow drops. A unit rated 9.4 GPM at a 70°F rise might deliver only 6.5 GPM at 80°F. Size for the cold months, not the summer brochure number.
For bigger households, two tankless units plumbed in parallel, or one dedicated to a high-demand primary bath, solve the flow ceiling without an oversized commercial unit. A licensed plumber can map your fixtures to a configuration before you commit.
Upfront costs: what drives the gap
Prices change and every home is different, so we won't quote dollar figures here. What we can explain is why the installed gap between tank and tankless is often bigger than people expect.
A like-for-like tank swap is usually simple: pull the old tank, set the new one, reconnect gas or electric and water, set the thermostat. Venting stays the same. A gas tankless install typically needs:
- A larger dedicated gas line for the bigger burner
- New venting (stainless steel, or PVC for condensing models) to an exterior wall
- Electrical service for the ignition and control board
- Mounting on a load-bearing wall
Whole-home electric tankless units often need a 200-amp panel and several high-amperage circuits, which can mean a panel upgrade. For a straight answer on your home, King will walk through it and give you a written quote. See our water heater installation and replacement page.
Manufacturer rebates, federal tax credits and utility incentives sometimes apply to high-efficiency models. Ask your plumber what's currently available in Chicago or Northwest Indiana when you get your quote.
Long-term costs and break-even
Three things shift the long-term math toward tankless: lower monthly energy use, longer life and fewer replacements.
- Energy use. Per the DOE, tankless is 24–34% more efficient for homes using 41 gallons a day or less, and 8–14% for high-use homes (around 86 gallons a day).
- Replacements. Over 20 years, most homeowners replace a tank at least once. A well-maintained tankless unit often lasts the whole stretch.
- Break-even. For most homes, the tankless premium is recovered somewhere between years 10 and 15. Moving within 5 years? A standard tank usually wins. Staying 10+ years? Tankless tends to make sense.
We won't promise exact savings, since they depend on usage and energy prices. The DOE numbers are a solid starting point for your own math.
If you have a recirculation pump
Hot water recirculation, common in larger or older homes with long pipe runs, changes the math. An always-on loop creates near-constant demand that can wear a tankless unit faster. The fix is a recirculation-ready tankless unit plus a pump that runs on demand or on a schedule. Mention an existing loop when you get quotes.
Which one is right for your home?
| Choose… | If… |
|---|---|
| A standard tank | You're on a tighter budget, may sell within 5 years, your gas line or venting would make tankless expensive, or your demand is moderate and predictable. |
| Tankless | You're staying long-term, tired of running out of hot water, want the floor space back, or you're remodeling and the gas and electrical work is already happening. |
| Two tankless units | You have 5+ people, bathrooms used at the same time, or high-demand fixtures like a soaking tub. |
| Replace sooner rather than later | Your tank is 10+ years old, rumbling, leaking at the base, making rusty water or needing repeat repairs. |
One safety component worth knowing: the pressure-relief valve.
Chicago-area considerations
- Hard water. Much of Chicago and Northwest Indiana has moderately hard to hard water, the biggest cause of early water heater failure here. In a tank, scale insulates the burner and can crack the liner. In a tankless unit, it coats the heat exchanger. Both need annual flushing, and a whole-home water softener helps either one last longer.
- Basement installs. Most local water heaters are in an unfinished basement. Tankless frees floor space, but gas units vent outside, so the location needs to be near an exterior wall.
- Older housing stock. Many homes were built before modern gas line sizing. Going tankless sometimes means upsizing the gas line from the meter. Factor it in when comparing quotes.
Permits and code
- City of Chicago. Installation and replacement generally require a plumbing permit, and the work must be done by a licensed Chicago plumber. Homeowners can't pull plumbing permits for their own properties.
- Suburbs and Northwest Indiana. Rules vary by municipality. Check with your local building department.
- Gas line sizing. Fuel gas code requires piping sized for all connected appliances at once. Tankless units draw much more gas, so a 1/2" line that worked for a tank often needs upsizing.
- Venting. Improper venting can create carbon monoxide hazards, a key reason this work is reserved for licensed pros.
- Resale. Unpermitted installs can complicate home sales and insurance claims.
Annual maintenance and flushing typically don't need a permit. Replacing a thermostat, anode rod or relief valve usually doesn't either, though gas valve and venting work generally does.
Keeping either system running longer
| Task | How often | What it involves |
|---|---|---|
| Tank flush | Yearly | Drain sediment, inspect the anode rod, test the relief valve. Step-by-step guide. |
| Tankless descaling | Yearly, more in hard water | Circulate descaler through the heat exchanger and clean the inlet filter. Tankless maintenance guide. |
| Anode rod check (tank) | Yearly, replace as consumed | Often used up in 3–5 years in hard water, sooner with a softener. |
| Temperature check | Each season | Keep it around 120°F to limit bacteria, scald risk and standby loss. |
Between visits, call a plumber promptly for standing water near the unit, a rotten-egg smell from hot water, a sudden drop in hot water, or any new error code. Slow leaks at the base of a tank often come days or weeks before a full failure.
Signs you're past repair
- The tank is 12+ years old and having problems
- Visible rust or water pooling at the base
- Hot water runs out noticeably sooner than it used to
- Loud rumbling or banging from the tank
- Rusty or metallic hot water that doesn't clear after flushing
- A repair estimate that's more than half the cost of a new unit
What a King water heater service call includes
- Visual inspection of the unit, gas or electric supply and connections
- Pressure-relief valve test
- Tank flush or tankless descaling, as appropriate
- Anode rod check on tank units
- Thermostat and burner or element check
- Inspection for leaks, corrosion and venting issues
- A written assessment of any recommended repairs or replacement timing
Parts (anode rod, thermostat, element, expansion tank, relief valve) are billed separately when needed. Softener installs and gas line upsizing are separate projects. We always quote them in writing before starting.
