The cost of replacing knob and tube wiring is $24,300 on average, and it costs between $12,000 and $36,600 for most people, depending on the size of the home and the electrical system specifics.
Replacing your home’s knob and tube wiring costs an average of $12,000 to $36,600, usually ranging from $10 to $20 per square foot. Your total bill depends on your home size, number of circuits, and the wiring’s accessibility. Knob and tube wiring is not considered safe for home electrical wiring due to its high shock and fire risk, making it essential to replace. Keep in mind that you should never attempt to alter any knob and tube wiring found in your home due to high safety risks. Instead, hire a professional electrician to complete the replacement safely.
Here are a few common costs for replacing a knob and tube electrical system. As with any project, cost factors include job size, materials, labor, permits, accessibility, disposal, and other variables.
It likely doesn’t come as a surprise that the square footage of your home and the number of rooms will impact the project price. Every room means additional wiring, fixtures, switches, and outlets. Costs average between $10 and $20 per square foot.
| Square Footage | Average Rewiring Cost |
|---|---|
| 800 | $8,000–$16,000 |
| 1,000 | $10,000–$20,000 |
| 1,300 | $13,000–$26,000 |
| 1,600 | $16,000–$32,000 |
| 2,000 | $20,000–$40,000 |
| 2,500 | $25,000–$50,000 |
| 3,000 | $30,000–$60,000 |
Since removing the old knob and tube wiring system requires cutting open the walls and ceilings, especially in an older home with outdated wiring, electricians will usually cut back the old wiring so it’s out of the way to install the new wiring. The rest of the old wiring is left in the walls.
If the electrician recommends removing the old wiring, you can expect additional labor time and disposal costs, depending on accessibility and difficulty. Plus, you’ll need to factor in the cost to repair the drywall or lath, ranging from $300 for small fixes to $900 for major repairs. And don’t forget to budget for the cost to repaint the walls, which averages $1,960 for the entire interior.
The most common materials electricians use for upgrading your knob and tube wiring include:
Electrical wiring, such as low-voltage, NM (non-metallic), UF (underground feeder), and THHN/THWN wire range in cost from $0.25 to $2.00 per linear foot.
Old work or retrofit electrical boxes cost between $2 and $6 per box. Retrofit boxes are designed for installation in remodels and renovations, as opposed to new work boxes that are designed to be attached to exposed studs during new construction.
Wire connectors cost about $0.20 each.
Professional electricians typically charge between $50 and $100 per hour to replace knob and tube wiring in your house, not including the cost of materials. Electricians will often charge per opening (each outlet, fixture, or switch), which is usually a flat rate of about $100 to $350 or more per opening. This charge may include prep to finish and clean-up, or those parts of the job may be added as separate items, depending on the electrician. While labor charges are an additional cost, they are essential as this project isn’t safe to complete without a professional electrician.
Most knob and tube wiring was installed in homes between the 1880s and the 1940s. If your home currently has knob and tube wiring, it’s likely older, making it more challenging to access and run new wiring. Difficult access to wiring and work spaces will increase the cost. For example, electricians may charge more if your home doesn’t have access to a basement, crawl space, or attic because they’ll likely have to open more walls, leading to more clean-up and repair costs.
Expect electrical permit costs to range from $10 to $500. The cost of permits will depend on the size and location of the job. The average cost range is from $100 to $125 per permit. Permits are necessary to replace the wiring in your home. It’s against the law to skip the permit for this type of electrical law, and failure to produce the appropriate permits could result in fines.
Before starting your knob and tube replacement work, your electrician will have a local building inspector visit the site to evaluate what needs to be done. After the work is complete, the electrician will have a post-inspection of the final product to make sure their work is up to code. Plan on spending from $100 to $150 per inspection.
Replacing knob and tube wiring typically means upgrading your electrical panel. Upgrading your electrical panel costs between $600 and $4,000 on average. Knob and tube systems usually run through a 60-amp electrical box and can’t support modern appliances designed for the present 100-amp panels. Ranging from 100 amps to 400 amps, the panel you need depends on how much electricity you need to power your home and appliances. Consult your electrician to get a professional opinion on the best electrical panel for your home’s needs.
It’s almost inevitable that unexpected costs will pop up, especially if your electrician finds surprise issues hidden in your walls. Here are a couple of cost factors to keep in mind as possible add-ons to the original project estimate.
As we mentioned above, you’ll likely have to invest in repairing your walls after the knob and tube replacement is complete. Depending on the age and build of the home, you may have drywall or lath and plaster walls that need to be patched or repaired after the electrical work is done.
Drywall patches and repairs typically cost anywhere from $60 to $900, or $50 to $150 per square foot, depending on the size and number of repairs. Lath and plaster typically costs an average of $80 to $200 per square foot.
After the job is done, your electrician or contractor will have some cleanup and disposal to do. This task typically costs about $300 to $500, depending on whether they haul it away or rent a dumpster. Once the dust settles, you may want to hire a professional cleaning service to refresh your home, which costs between $30 to $50 per hour, depending on the home and job size.
Replacing knob and tube wiring systems with more modern electrical systems often involves upgrading the things the system powers, like outlets, switches, and lights. Since a knob and tube wiring system is not grounded and it’s designed for 60 amps, it can’t support most modern appliances and electronics that require a grounded 100-amp electrical system.
Additionally, the National Electrical Code (NEC) requires that each room has an electrical outlet or receptacle at least every 12 feet. It’s likely that you’ll need to install some outlets to bring the electrical in your home up to code. You can expect the following upgrades and additions to cost as follows:
| Upgrade Installation | Cost Per Item |
|---|---|
| GFCI grounded outlet | $10–$25 each outlet |
| New electrical outlet | $140–$300 per outlet |
| Replace existing outlet | $125–$250 per outlet |
| New light switch | $100–$200 per switch |
| Replace existing light switch | $50–$150 per switch |
| Smart outlet | $25–$50 each outlet |
| Light fixture | $160–$950 each fixture |
| Ceiling fan | $150–$360 |
Although you don’t want to cut corners when replacing knob and tube wiring with a more modern electrical system, you can save money in a couple other ways. While professional electricians need to handle the main job of the replacement, you can cut down on costs by completing some of the pre- and post-work tasks.
Choose less expensive fixtures: Since you’ll likely need to replace light and outlet fixtures, you can reduce costs by opting for less expensive models.
Patch the drywall or plaster yourself: If you need to restore your drywall after the electrician opens the walls during the replacement process, attempt a DIY drywall repair to save on labor costs.
Touch up the paint yourself: Like the drywall repair, you can likely touch up the ceiling paint and walls on your own post-wiring replacement.
Clean up debris yourself: Instead of paying extra for the pros to clean up the debris from the knob and tube replacement, take care of it yourself. For major jobs, consider using a junk removal service, costing an average of $240.
Household wiring, especially electrical work of this scope, must be done by a trained and licensed local electrician. Homeowners should not attempt to alter or replace knob and tube wiring, as it’s a dangerous undertaking and could result in injury or fire. Ultimately, completing this type of electrical work without a license is illegal and you won’t be able to get the permits needed to carry out the project. Hiring a professional electrician is the only way to go on this one.
It’s okay to buy a house with knob and tube wiring if it’s safe, functional, and still in good condition as well as a minimum of 60 amps. However, a professional should conduct an electrical inspection of the knob and tube wiring to ensure it’s up to code as well as safe and functional. However, the usual 60-amp service boxes can’t handle electricity from 100-amp breakers, making it difficult or impossible to power modern devices.
The copper wire used in knob and tube wiring systems can last up to 100 years. However, it’s considered a dangerous and outdated wiring method because the cloth, fabric, or rubber insulation sheathing can become brittle and fall apart. Knob and tube wiring systems should be inspected if you’re considering buying a home with this type of wiring, or if you have problems with frequently tripping breakers, a sign that you may need to replace them.
Replacing knob and tube wiring takes anywhere from one to three weeks, depending on the scope of the project. Of course, this assumes the removal and replacement of knob and tube wiring throughout the entire home. Smaller jobs will take less time. The timeframe also depends on the size of the home and the specifics of the construction. Accessibility concerns also play a role here. No matter how you slice it, this is a massive undertaking for even the most seasoned DIYers.
If the knob and tube wiring system is in good condition and recently approved by a licensed inspection, then it is safe. However, knob and tube wiring is not grounded, and the insulation sheathing can deteriorate and leave exposed wires inside walls and other areas that can cause potential fire or shock hazards. Always have a professional inspect or modify any part of knob and tube electrical systems.
