Yes, if you are swapping a gas storage tank for a tankless or on-demand gas unit. Mesa's residential FAQ lists that change as permit required. A like-for-like replacement of equal or lesser rating does not need one, but the gas utility must be told before the new appliance is energized.
What does Mesa say about tank to tankless?
The city's Residential Construction FAQ has a short entry on replacing a water heater. It gives three lines.
- No permit required: residential replacements of gas and electric water heaters of equal or lesser rating using a like for like model.
- Permit required: "For residential replacement of a traditional (storage) gas water heater with a tankless or on-demand gas water heater."
- Notification required: "Notify the serving Gas Utility before placing gas appliances into service."
So the answer for your project depends on what goes in. A tank for a matching tank has no permit. A gas tank for a gas tankless needs one. The notice to the gas utility applies to gas appliances either way.
Phoenix has its own rule for this job, and it is not the same. Our page on water heater permits in Phoenix explains it. Scottsdale lists a gas or electric water heater replacement as Minimum Permit work. If you own property in more than one city, look up each one. Do not assume the rule carries over.
What does the Mesa City Code say?
The FAQ is a summary. The rule sits in Mesa City Code Section 4-1-4, "Permits." Subsection (A) says that anyone who intends to install, alter, repair, remove, convert or replace any electrical, gas, mechanical or plumbing system covered by the code must first apply to the Building Safety Director and get the required permit or permits.
Subsection (B) then lists work that does not need a permit. Two entries matter for water heaters.
Gas water heaters. The fuel gas list exempts "Replacement of gas water heating appliances of equal or less Btu/cfh rating and minor modification to electrical, plumbing, and mechanical connections necessary to serve the new appliance" in homes and other dwelling units. The exemption has a condition: "provided the serving Gas Utility is notified prior to the appliance being energized."
Electric water heaters. The plumbing list exempts "Replacement of electric water heating appliances of equal or less amperage rating, and minor modification to electrical, plumbing, and mechanical connections to serve the appliance" in the same kinds of dwellings.
Both exemptions use the words "equal or less." They cover a replacement that matches the old unit or is smaller. The FAQ treats a tank to tankless change differently. It lists that change as permit required. If you are moving from an electric tank to an electric tankless unit, compare the amperage on the two nameplates. If the new unit is rated for more amperage than the old one, it does not fit the exemption, and you should ask the city before you start.
The code also says that an exemption "shall not be deemed to grant authorization for any work to be done in any manner in violation of the provisions of this Chapter or the technical codes." In other words, work that needs no permit still has to meet the plumbing, gas and mechanical codes.
How do you apply, and what does the city check?
The code says an applicant files a written application on a form furnished by the Building Safety Division, with a description of the work, the address and the use of the space. The city's FAQ lists Permit Services at 480-644-4273 for construction permit and building code questions, so call there if you are not sure which permits your job needs.
Two parts of the code shape the process.
- Contractor license. The application section, 4-1-4(H), says each applicant for a building permit "shall affirm by affidavit compliance with ARS Title 32, Chapter 10, and ARS 42-5005." If an applicant claims an exemption from licensing, the affidavit has to give the basis and the name and license number of the contractors doing the work.
- Inspection before connection. Section 4-1-5 says that building service equipment regulated by the technical codes "shall not be connected to the water, fuel, or power supply, or sewer system until authorized by the Building Safety Director." For a tankless heater, that means the gas and water hookups are approved through inspection, not just installed and used.
The same section says construction or work for which a permit is required "shall remain accessible and exposed for inspection purposes until approved," and that the permit holder or an authorized agent must notify the city when work is ready for inspection. Plan your install so the gas piping, venting and connections are visible when the inspector arrives.
If a permit is issued and the work never starts, section 4-1-4 says the permit becomes invalid if the work is not commenced within 180 days after issuance, or if the work is suspended or abandoned for 180 days after it begins.
How do the gas line and the gas utility notice fit in?
A tankless heater may call for a different gas line than the tank did, so the permit is a good time to check it. We cannot say what your line can handle without looking at it, but the manufacturers explain the method.
Rinnai says its tankless water heaters are designed to use either a 3/4 inch or 1/2 inch gas line "as long as sufficient gas flow is available." It adds that an undersized gas line can stress a tankless system and possibly reduce its lifespan. Its steps for sizing a gas line include the type of gas, the inlet pressure, the allowed pressure drop, and "what other types of gas appliances are sharing the gas line," along with the maximum loads for the whole system as stated in the National Fuel Gas Code.
Navien's installation manual says installation and service "must be performed by a qualified installer, service agency or the gas supplier," and that the installation "must conform with local codes or, in the absence of local codes, the National Fuel Gas Code." Mesa is a local code jurisdiction, so the city's rules come first.
The gas utility notice. The notice is easy to miss. Both the FAQ and the code say the serving Gas Utility must be notified before a gas appliance is put into service. In the code, that notice is a condition of the exemption for a like-for-like gas water heater. If you skip it, the exemption does not apply. The FAQ lists it as its own line, "Notification required," on top of the permit rule. Ask your installer who makes the call and when. Do not light or energize the new unit until it has happened.
Our guide to gas vs. electric water heaters covers fuel choice, and how tankless water heaters fail in the Valley covers what to expect after the install. If your home is all electric, see our page on whether electric tankless water heaters work in Arizona.
When should you call a plumber?
Call a plumber for any tank to tankless swap. The job touches the gas piping, the venting, the water connections and often the electrical supply, and the city inspects permitted work. A licensed installer can also tell you whether your existing gas line can feed the unit, and how the vent has to run.
If your old heater fails on a weekend and you need hot water fast, read can I fix a Mesa plumbing emergency before a permit first. It explains Mesa's emergency repair rule.
Talk through a tankless upgrade with HQ Plumbing and Air before you apply for the permit. We are licensed and insured, and we give free estimates with the price up front.