Replacing a water heater in Illinois: what to know first

Who regulates plumbing in Illinois

The Illinois Department of Public Health (IDPH) licenses plumbers, plumbing contractors and apprentice plumbers under the Illinois Plumbing License Law (225 ILCS 320)^[2]. IDPH runs an online plumbing license verification tool, so you can check a plumber's license before you hire^[2]. The law also requires plumbing contractors to be registered, and requires at least one licensed plumber among the members or officers of any company engaged in plumbing work^[1].

Who may install or replace a water heater

Licensed plumbers. The law states that all planning and designing of plumbing systems and all plumbing shall be performed only by licensed plumbers and licensed apprentice plumbers working under supervision^[1]. Replacing a water heater means disconnecting and reconnecting the home's water supply, so treat it as licensed plumbing work.

The owner-occupant exception, read carefully. Section 3(2) of the law lets the owner-occupant or lessee-occupant of a single-family home plan, install, alter or repair the plumbing of that home, with conditions^[1]:

• The work must meet the Illinois State Plumbing Code and is subject to inspection.
• The owner may not employ anyone other than a licensed plumber to assist.
• "Occupant" means you live there as your sole residence and intend to keep living there for at least 6 months after the work. Moving out sooner creates a presumption you did not intend to stay.

That is narrower than the "anyone can install their own water heater" advice you see online. It does not cover rentals you do not live in, multi-unit buildings, or paid unlicensed helpers.

Gas and electrical. Gas connections, venting, and any new 240-volt circuit add their own requirements. A licensed plumber handles the gas side; a new circuit needs a licensed electrician.

Permits

Permit rules are set locally in Illinois, and they differ.

Chicago. The City of Chicago's Department of Buildings lists "repairing or replacing (in-kind) a hot water heater" among work that does not require a building permit in a residential building up to 4 stories above grade^[3]. In-kind means the same type, size and shape. The city adds that work done without a permit must still comply with all Chicago Construction Codes^[3]. Changing the type (tank to tankless), size or location is not in-kind and should be checked with the Department of Buildings first. Several websites say a permit is always required in Chicago; the city's own page says otherwise for in-kind swaps.

Elsewhere. Outside Chicago, each village or city sets its own permit rules for water heater replacement. Call your building department before work starts. Where a permit is required, the licensed plumber usually pulls it.

Rebates in Illinois (as of October 2026)

Utility	Rebate	Conditions
ComEd	$750 for an ENERGY STAR heat pump water heater	Purchased July 1 to December 31, 2026; apply within 60 days of purchase or by February 28, 2027, whichever comes first; installed at your ComEd service address; higher amounts for income-eligible customers[4]
Nicor Gas	$225 for an ENERGY STAR gas tank with UEF .86 or higher; $150 for an ENERGY STAR tankless with UEF .95 or higher	Available January 1 to December 31, 2026; one rebate per account; instant discounts through participating contractors[5]

We have not yet confirmed current water heater rebates from Peoples Gas or Ameren Illinois; check their own rebate pages. The federal 25C credit does not apply to water heaters placed in service after December 31, 2025^[7].

Hard water

Chicago's Lake Michigan water typically runs 130 to 150 mg/L as calcium carbonate, or 7.6 to 8.8 grains per gallon, per the city^[6]. At that level, flush tanks on the maker's schedule and descale tankless units when they ask for it. Suburbs on well water or other sources can differ; check your utility's water quality report.

When to call a pro

• Any replacement if you rent, do not live in the home, or would need a helper.
• Changing from tank to tankless, or changing size or location (not in-kind).
• Gas line, venting, relief valve or electrical work.
• To claim a utility rebate that requires a contractor invoice or instant discount.