Updating Knob and Tube Wiring for an Older Home

By Dave Rongey - Summary:

Is it common practice to add new wire with old knob and tube wiring? How to Replace Knob and Tube Wiring, Replacing Old Electrical Wiring, What Areas of the Home to Rewire First.

Guide to Replacing Outdated Electrical Wiring

Electrical Question: Is it common practice to add new wire with old knob and tube wiring?

I’m purchasing a 1910 home with updated 100amp service box located in the basement.

  • There is all new wiring in basement, and it seems like all the wiring has been replaced in 1st floor kitchen and bathroom only, but not the front of house dining room and living room, and not the 2nd floor, which all have knob and tube wiring.
  • I asked to have the knob and tube wiring updated. The electrician ran approx 3ft of new wire to a new electric outlet in one bedroom and claims this is his version of updating knob and tube wiring.
  • I feel this old wiring is a serious fire hazard and wonder if it is common practice to mess with knob and tube and add new wiring to it?

Please help!
Thanks, Ruth.

This electrical wiring question came from Ruth, in Allentown, Pennsylvania.

Additional Comments: Love your website!

Dave’s Reply:
Thanks for your electrical question Ruth.

Replacing Old Knob and Tube Electrical Wiring

  • Replacing Outdated Electrical Wiring
    • Updating home electrical wiring from old knob and tube to the current electrical codes can be an extensive project, but it is always recommended.
    • Most of the cost to upgrade knob and tube wiring will be for the labor that is required to access the old wiring and install the new wiring.
    • Knob and tube wiring can be a fire hazard depending on the condition of the wiring where the old cloth type insulation may deteriorate over time. All things considered, it is always best to upgrade the home wiring to the current electrical codes.
  • What Areas of the Home to Rewire First
    • Upgrading the kitchen and bathrooms is always a good place to start which will involve new circuits and GFCI protection, and it sounds like this may have been done, so that is good.
    • Installing smoke detectors is also extremely important for an older home with outdated electrical wiring.
  • Adding Additional Wall Outlets
    • As for the 3 feet of wire that was installed, it sounds like that was to install an additional outlet, and hopefully the electrician branched off of one of the upgraded circuits.
    • The problem with adding new cable to existing knob and tube wiring is that the old knob and tube wiring did not have a ground wire, so if a new 3wire cable is installed for a new outlet the ground wire will not be connected to the electrical system ground unless an additional ground wire is installed and connected to the electrical panel ground system.
  • The Cost of  Upgrading Home Electrical Wiring
    • When a home is being sold and the electrical system is required to be updated and brought up to code it will add to the value of the home, and the investment for the project cost will need to be supplied by either the seller or the buyer.
    • Commonly this will be handled and agreed upon within the specific negotiations regarding your transaction.
    • For homes that are not involved in a sales transaction, the cost of upgrading the electrical wiring will depend on the going rate for qualified electricians in your area, the size of the home, the extent of the specific project, and the available access to remove the old knob and tube wiring and replace it with new wiring.  Labor will account for approximately half of the overall project cost.
  • When is the Best Time to Update Home Wiring?
    • In my experience, it is best to update the wiring when performing a remodel project, especially for the kitchen area.
    • A remodel project typically involves replacing old plumbing as well and other systems, so it is best to open up one side of each wall where the plumbing and electrical systems are located, this way the workers will have unobstructed access to perform the work which will save on labor costs.
    • It is always best to get at least three competitive bids from local licensed contractors which include a detailed list of the scope of the project with all the details clearly explained.

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FAQs Frequently Asked Questions and Comments

2 Responses to “Updating Knob and Tube Wiring for an Older Home”
  1. Dave Rongey says:

    Hi Curtis,
    I would definitely install new dedicated circuits for the baseboard heaters that will be installed. The new circuits should be sized according to the electrical requirements of the new baseboard heaters.
    I hope this helps,

  2. CURTIS SCOTT says:

    I have a question about adding four 120 volt Baseboard heaters to and older house with Knob and Tube wiring.


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