What is involved in installing a water heater to code?

If you smell gas

Stop here. Do not light anything or use switches or phones inside. Leave the building, then call the gas utility or 911 from outside^[14]. No installation question is more urgent than that.

What this section covers

A water heater install is plumbing, and for gas units it is also fuel gas and venting work. For electric and heat pump units it includes a 240-volt circuit in most cases. This section explains each part so you can read a quote, ask the right questions and know which jobs are licensed work. It does not give step-by-step instructions for gas, venting, relief valve or electrical work: those belong to an independent licensed plumber or electrician.

Guide	What it answers
Do you need a permit?	When a permit is required and who pulls it
Who can legally install a water heater, by state	Licensing and homeowner exemptions
What a replacement install includes	The scope a complete quote should list
Expansion tank requirements	Closed systems and thermal expansion
Drain pans and relief valve discharge	Where pans are required and how the discharge pipe must run
Venting requirements	Atmospheric, power vent, direct vent and condensing vents
Gas line sizing for tankless	Why tankless often needs a bigger gas line
Electrical requirements and breaker sizing	Circuits for tanks, tankless and heat pumps
Converting tank to tankless	Gas, vent, water and condensate changes
Switching gas to heat pump	Circuit, space and condensate needs
Moving a water heater	New lines, vent routes and costs
Attic, garage, closet and outdoor installs	Location-specific rules

Permits: set locally, and they differ

There is no national permit rule for water heaters. Three examples show the range:

• Houston requires a plumbing permit to install or replace a water heater, and the permit must be obtained by a master plumber registered with the city^[2].
• Chicago lists in-kind replacement of a hot water heater in a residential building up to 4 stories as work that does not need a building permit, though the work must still meet the city's codes^[3]. A change in type, size or location is not in-kind.
• Hamilton County, Ohio requires a plumbing permit and inspection for all new and replacement water heaters^[4].

Call your building or health department before work starts, or ask the plumber which office issues the permit for your address.

Who may do the work

Licensing is set by each state, and some states leave residential work to local governments.

• Texas. Plumbers are licensed by the Texas State Board of Plumbing Examiners (TSBPE)^[16]. State law lets a property owner do plumbing in their own homestead without a license^[1], but city permit rules still apply, such as Houston's master plumber requirement^[2].
• Illinois. An owner-occupant of a single-family home may do their own plumbing, to code and subject to inspection, and may not employ anyone but a licensed plumber to help^[5].
• Ohio. The state licenses commercial plumbing contractors; residential contractors are regulated by local building and health departments^[15].

Gas piping and new circuits often carry separate license and permit requirements. See who can legally install a water heater.

What inspectors commonly check

These are the model code items most often tied to water heaters. Your city may have adopted a different edition or local changes.

Item	What the model code says
Relief valve discharge pipe	No valve, no tee, no threaded end; drains by gravity; ends where people can see it[7]
Thermal expansion control	Required where a check valve, backflow preventer or similar device creates a closed system with a storage heater[8]
Drain pan	Required where a leak would cause damage[6]
Garage installs	Heaters with an ignition source must have it at least 18 inches above the garage floor, unless listed as flammable vapor ignition-resistant[9]
Electrical circuit	Storage heaters of 120 gallons or less are sized as continuous loads, with the circuit rated at least 125% of the heater's rating[10]
Gas units	Venting, combustion air, gas shutoff and connector; checked by the inspector and set by the fuel gas code your city uses

See expansion tanks and drain pans and relief valve discharge.

Gas, venting and electrical: explained, not DIY

Gas lines. A gas water heater needs a gas line sized for its input rating and for everything else on the same line. Tankless units have much higher burner inputs than tanks, which is why a conversion often needs a larger line. An undersized line is one of the causes makers list for flame-loss codes (see Rinnai codes). See gas line sizing for tankless.

Venting. Exhaust gases contain carbon monoxide. Atmospheric tanks use a draft hood and a metal vent; power vent, direct vent and condensing units use fans and specific pipe materials set by the maker's manual. A vent that is the wrong size, material or slope can spill exhaust into the home. See venting requirements.

Electrical. Electric tanks and most heat pump units need a dedicated 240-volt circuit sized to the heater's rating^[10]. Whole-house electric tankless units can need several large circuits and sometimes a panel upgrade. A new circuit is a job for a licensed electrician. See electrical requirements.

Changing type or fuel

Changing what you have is where installs get bigger:

• Tank to tankless: often a larger gas line, new venting and a condensate drain on condensing units. See converting tank to tankless.
• Gas to heat pump: a 240-volt circuit in most cases, enough space and air around the unit per its manual, and a condensate drain. See switching gas to heat pump.
• Moving the heater: new water, drain and vent or circuit runs. HomeGuide's January 2026 range for relocating a water heater is $500 to $2,500^[11]. See moving a water heater.

Plan ahead for the federal efficiency rule. DOE's 2024 standard applies to units made on or after May 6, 2029^[13], and for electric storage heaters in the most common sizes it sets efficiency at the level of an entry-level heat pump^[12]. It does not require replacing a heater you already own.

Location matters

Attics, closets, garages and outdoor spots each add rules: a pan where a leak would cause damage^[6], ignition-source height in garages^[9], access and clearance per the maker's manual, and freeze protection outdoors. See attic, garage, closet and outdoor installs.

What it costs

HomeGuide's January 2026 range for a standard tank installed is $600 to $3,100, with tankless at $1,400 to $5,600^[11]. Code upgrades, permits and location changes add to that. See installation cost for line items.

When to call a pro

• Any gas line, gas connector, venting or relief valve work.
• Any new or changed electrical circuit (a licensed electrician).
• A change in fuel, type or location, or an install in an attic or closet.
• When you are unsure whether your city requires a permit or who may pull it.