Knob and Tube Wiring in Ontario: Code Status, Risks, Assessment and Replacement

Knob and tube wiring in Ontario sits in an odd legal spot. Nobody is allowed to install it any more, yet a house that still has it is not automatically out of compliance. Insurers, buyers and renovation contractors all react to it differently, and the advice homeowners read online often comes from other provinces or from the United States. This guide sticks to what Ontario's own regulators say: the Electrical Safety Authority (ESA), which administers the Ontario Electrical Safety Code, and Natural Resources Canada, which publishes the federal guidance on insulating older houses. It then walks through how the wiring is found, assessed, replaced in phases and priced.

What knob and tube is and when it went into Ontario homes

Knob and tube is the earliest form of permanent house wiring. Instead of a cable that bundles conductors inside one jacket, each wire runs on its own. White ceramic knobs hold the conductors away from joists and studs, and ceramic tubes protect them where they pass through framing. The conductors are wrapped in a rubber-like insulation that, according to ESA, can turn brittle as it ages. There is no bonding conductor, which is why so many of these houses still have two-slot receptacles.

ESA dates the method to homes built from the early 1900s to the 1940s and notes that it is no longer used. Age of construction is therefore the first clue. In the City of Toronto, the 2021 Census ward profiles show how concentrated older housing is: Beaches-East York counts 55.3% of its 45,710 private dwellings in the "1960 or before" bracket, and University-Rosedale counts 40.1% of 53,505, against 29.3% for the city as a whole. That bracket runs well past the 1940s, so the numbers do not tell you how many homes still carry knob and tube, but they do show where a pre-war house is most likely to turn up on a listing.

Code status: what the 2021 Ontario Electrical Safety Code changed

The 28th edition of the Ontario Electrical Safety Code, published in 2021, deleted the rules for installing knob and tube. ESA is clear that the Code is not retroactive, so removing those rules did not order existing wiring out of Ontario homes.

ESA's Flash 25-05-FL (May 2025) spells out when concealed knob and tube may stay in service. Conductors hidden in walls and floor spaces that feed general lighting and receptacle circuits can remain in place if three conditions hold:

1. The circuit is protected by a 15 A fuse or breaker. 2. No outlets have been added that overload the circuit. 3. The conductors you can see are in sound condition.

The same flash notice adds a practical point about receptacles. Where a three-prong receptacle is needed on a knob and tube circuit, only a GFCI receptacle should be used. Removing the ground pin from a plug or power bar to fit a two-slot outlet is not permitted, and two-pin to three-pin adapters are not allowed. A GFCI receptacle does not create a ground; it trips when current leaks, which is a different kind of protection.

The dangers ESA and NRCan describe

ESA's position is measured: it calls knob and tube safe when a Licensed Electrical Contractor maintains it properly. The risks it lists come from age and from what later owners did to the system, not from the original design alone.

The unsafe practices named in Flash 25-05-FL are worth reading as a checklist for your own house:

- 20 A or 30 A fuses screwed in where a 15 A fuse belongs, which lets the old conductors carry more current than they were sized for; - extension cords used as permanent wiring, or cords too small for the load; - ground pins snapped off so three-prong plugs fit two-slot receptacles; - two-pin to three-pin adapters.

Insulation contact is the other hazard, and it matters most during energy retrofits. Natural Resources Canada's Keeping the Heat In guide warns against letting loose-fill insulation touch old knob-and-tube wiring, chimneys, combustion vents or exposed recessed light fixtures, because these create a fire risk. The original installation relied on open air around each conductor to shed heat. Blowing cellulose or fibreglass over a live run in the attic or into a wall cavity removes that air. If an insulation upgrade is on your list, settle the wiring question first.

ESA also says conductors should be replaced wherever the exposed wiring shows mechanical damage, deterioration, poor connections, overheating or alterations made because of overloading. If you ever see smoke, sparking or flame at a fixture or outlet, leave the house and call 911.

How to tell whether your house has it

ESA's technical podcast on the subject notes that an unfinished basement makes the job easy: look up at the joists. Separate insulated conductors held on white ceramic knobs and passing through white ceramic tubes are the signature. Other clues you can check without opening anything:

- two-slot receptacles in the older rooms, a direct result of the missing bond wire; - a fuse panel, or 15 A circuits feeding the original part of the house; - single conductors on knobs in an accessible attic, which is also where the insulation risk sits.

A finished basement or a previous partial rewire hides much of the evidence. ESA points out that many owners have already replaced the exposed runs where wiring goes up the walls, so the visible wiring may be modern while the concealed branch circuits upstairs are still original. Confirmation therefore usually means opening a few device boxes and looking at the conductors behind them, which is a job for a licensed contractor rather than a home inspector.

Getting a proper assessment

ESA recommends hiring a Licensed Electrical Contractor (LEC) to assess a house that has knob and tube. It stresses that this is not the same as a home inspection, because the assessment looks only at the electrical system. ESA also recognizes a formal Electrical System Safety Assessment, which an LEC business can perform to review wiring and devices for hazards; ESA's own checklist for that assessment asks the contractor to record whether the wire type is copper, knob and tube or aluminum.

A useful assessment should give you answers to five questions:

1. Which circuits are still live on knob and tube, and which have already been replaced? 2. Is each knob and tube circuit protected at 15 A? 3. Are any conductors damaged, brittle, spliced badly or showing signs of heat? 4. Has insulation been installed against any live run? 5. Which rooms will be opened anyway during planned renovations?

Before booking, check the contractor's licence. ESA's Contractor Locator lets you search by name, licence number or phone, and only a licence showing as valid means the business may do the work.

Replacement process and phasing

Replacing knob and tube is a rewire of the original circuits, and it rarely has to happen all at once. Owners commonly split it into phases that follow the rest of their plans:

- Phase 1, the service end: if the house still runs on fuses or an undersized panel, a new panel with breakers comes first, so the new circuits have somewhere to land. - Phase 2, open areas: the basement and attic, where new cable can be run with little or no drywall work, and where the insulation conflict NRCan describes is most likely. - Phase 3, finished rooms: walls and ceilings are fished from above and below, with small access holes patched afterward. Kitchens and bathrooms planned for renovation are often timed so the rewire happens while the walls are open. - Phase 4, decommissioning: every abandoned knob and tube run is disconnected at both ends so nothing old remains energized.

Each phase is its own piece of electrical work and is reported to ESA. Keep the contractor's notification numbers and the ESA Certificate of Acceptance for each one, because those are what prove which circuits have been replaced. If the panel change requires the utility to disconnect power, the new installation has to pass ESA's inspection before the service is turned back on.

Knob and tube wiring replacement cost

KV Bear Electrical publishes one range for this work: full knob and tube removal in a typical Ontario home runs from $8,000 to $20,000+ (as of October 2026). Where a house sits in that range depends on three things the business names on its service page: the size of the home, how accessible the walls and ceilings are, and how much knob and tube is still in service. Houses with only partial knob and tube tend to fall at the lower end.

When you compare the cost to replace knob and tube wiring across quotes, check that each one covers the same scope. A fair comparison lists the number of circuits to be replaced, whether a panel change is included, how much drywall patching is in the price, whether old runs will be disconnected at both ends, and that the ESA notification is part of the job. A quote that skips any of those items is not cheaper in the end; it simply leaves work for later. Phasing spreads the spending across several projects, but the total is usually lower when phases line up with renovations you were already planning, since open walls cost less to wire than finished ones.

Permits, records and who files what

Almost all electrical work in Ontario must be reported to ESA through a notification, also called a permit. When you hire an LEC, the contractor files it. ESA's do-it-yourself rules let a homeowner wire their own home only after filing the notification themselves, and they bar friends, relatives and handymen from doing the work for you. ESA's bulletin on minor homeowner repairs also excludes ungrounded wiring from its exemptions, which covers knob and tube circuits.

After the work passes inspection, ESA issues a Certificate of Acceptance. ESA describes it as an important document for insurance and resale and tells owners to ask their contractor for a copy. File one per phase.

Toronto and other municipal angles

The City of Toronto does not regulate knob and tube directly, but several of its rules touch the work.

- Electrical permits are separate. The City's BuildSafeTO guidance says almost all electrical work in Ontario needs an ESA permit, which is obtained separately from a City building permit. A rewire on its own goes through ESA, not the City. - Property standards. Toronto Municipal Code Chapter 629 requires every dwelling unit to have enough electrical outlets that extension cords are not used as a permanent wiring system. Older houses with a single outlet per room are where that rule bites, so adding grounded circuits during a rewire helps with both safety and property standards. - Heritage districts. For properties in Toronto's heritage conservation districts, the City says interior alterations do not need a heritage permit, so rewiring from the inside is not held up by that process. - Reconnection. Toronto Hydro reminds customers that finished electrical work needs an ESA inspection, after which ESA authorizes Toronto Hydro to energize or re-energize the service.

Outside Toronto the ESA rules are identical, but the utility differs. In Durham communities such as Whitby, Ajax, Pickering and Clarington, Elexicon Energy handles power shut-offs for a panel change; it gives each residential customer one free service isolation every 12 months during regular business hours and charges for additional ones in that window (as of October 2026).

Insurance, briefly

ESA notes that many insurers will not provide or renew coverage on homes with knob and tube because they see it as a higher risk, and some ask for replacement first. The details of quotes, surcharges and what to send your insurer are covered in our separate post on knob and tube wiring insurance. The short version: the assessment report and the Certificates of Acceptance from each replacement phase are the documents insurers ask for. To book an assessment or a quote on a phased rewire, call KV Bear Electrical at 905-999-5048.