Quick answer
A like-for-like water heater replacement in a house usually needs no building permit in Ontario, but the municipality decides: Toronto lists hot water tanks among work that needs none, while Burlington and Mississauga do not name them. A fuel switch, a relocation or a new vent through a wall can change the answer. Gas work always needs a TSSA-licensed technician, and new electrical circuits need an ESA notification.
Whether you need a permit to replace a water heater in Ontario depends on what is changing and which building department you fall under. There is no single province-wide line that says water heater swaps are exempt. The Building Code Act is enforced municipality by municipality, each building department publishes its own list of work it does and does not ask a permit for, and the gas and electrical rules apply whatever that list says.
Like-for-like replacement versus changes that pull in other rules
Same fuel, same location, same venting and similar size is the simple case, and it is the one municipalities generally leave alone. The jobs below are not simple swaps, and each is worth a call to the building department before work starts.
- Fuel switch: electric to gas brings a new gas line and a vent; gas to electric or to a heat-pump water heater brings a new electrical circuit.
- Relocating the tank: moving it across the basement means new water piping and sometimes a new drain connection. Mississauga, for one, asks for a permit when a plumbing fixture is added, removed or relocated.
- A new vent termination through a wall: going from a chimney-vented tank to a power-vent or direct-vent model puts a new hole in the building envelope, and CSA B149.1 sets how far that termination must sit from windows, doors, air intakes and the gas meter.
- Tank to tankless: a tankless unit draws far more gas at once, so the line often has to be upsized (typically +$400–$1,200) and the venting is all new.
What is always required, permit or no permit
- Gas work by a TSSA-registered contractor: the connection, venting and start-up of a gas water heater are done by a certified gas technician, G2 or higher, to the CSA B149.1 natural gas and propane installation code. A building permit exemption does not change that.
- ESA notification for new electrical circuits: a new or upsized circuit for an electric or heat-pump tank is electrical work that has to be filed with the Electrical Safety Authority, normally by the licensed electrical contractor doing it.
- The manufacturer's installation instructions: clearances, vent lengths and the relief valve discharge pipe are part of the certified installation, not options.
What TSSA licensing means for the person in your basement, and why it matters for insurance, is covered in can I install my own water heater in Ontario.
What local building departments publish (checked October 2026)
- City of Toronto: its list of work that does not need a building permit includes installing hot water tanks in a house. Installing or modifying heating or plumbing systems is on the list that does.
- City of Burlington: exempts like-for-like replacement of heating and cooling equipment in a house, and replacing plumbing fixtures of the same type in the same location. Water heaters are not named, and the city treats anything not on its exemption list as needing a permit, so confirm a non-standard job.
- City of Mississauga: no permit for a plumbing fixture replaced in the same location. Water heaters are not named on either list, and the city does ask for a permit when a furnace is replaced with a higher-efficiency one, so do not assume every mechanical swap is exempt there.
- Town of Oakville, City of Hamilton, Town of Milton and others: we did not find a published line that names water heaters. Ask the building department before a relocation, a fuel switch or a new wall vent.
These pages change, and a counter clerk's answer for your address beats any summary. Our city guides, such as HVAC permits in Burlington, go further into each department's process.
Who applies, and what to keep on file afterwards
When a permit is needed, either the owner or the contractor can apply; settle which before the job is booked, and have the fee shown on the quote. For every installation, permit or not, keep the invoice showing the contractor's TSSA registration, the technician's name, and the ESA certificate if electrical work was done. A buyer's lawyer, a home inspector or your insurer may ask for them years later.
For budgeting, a straight tank-for-tank replacement is $1,200–$2,500 installed and a tankless conversion $3,500–$6,500; permit fees, where they apply, are set by the municipality. ZK Mechanical's technicians are TSSA-licensed, and we tell you at the quote stage whether your job is a simple swap or one that needs the building department. Start with the water heater service page or describe the job to us.