Knob and Tube

Check out our Knob and Tube Guide on Amazon!

A Homeowner’s Guide to Knob and Tube Wiring Replacement
Author: Jesse Kuhlman, Owner Kuhlman Electrical Services

Is now available for download our digital guide, especially made for those who want to upgrade the old electrical wiring system of their residence or want to know more about knob and tube wiring replacement.


Click here to buy on

The knob and tube wiring team at KES

We specialize in knob and tube wiring mapping and remediation. We have worked in countless homes and bring the experience you need when it comes to knob and tube replacement. Most homes on the North Shore and throughout Boston have similar home “types” which gives us the advantage of knowing the tricks and methods to replace your knob and tube wiring with the least damage to your plastered walls. We handle knob and tube wiring replacement jobs year-round, some jobs taking a few days, and some up to 4-5 weeks. When I say we specialize in this kind of wiring, I mean it.

Disadvantages of Knob and Tube wiring

Unfinished attic or basement insulation companies cannot insulate your home with knob and tube wiring. The knob and tube wiring is run between joists with air space to dissipate heat. When insulation (whether it’s blown in or standard pink insulation) is surrounding the knob and tube wiring, it can overheat and potentially cause a fire hazard. The insulation company will require an electrician to inspect all wiring to confirm that there is no concealed knob and tube. If knob and tube is found, it must be rewired to the standard set forth in the 2014 NEC (National Electrical Code).

Knob and tube wiring was never meant to last 100+ years. Homeowners sometimes take out the proper 15 amp or 20 amp fuse and install a 30 amp fuse because they do not have enough power. Yes, this will prevent your fuse from blowing but it creates a fire hazard. The knob and tube wiring that is now overfused was not meant to carry such a high current and the wire insulation can begin to break down.

Squirrels, mice and other critters seem to love the insulation on this knob and tube wiring style. These pests can can leave bare copper wire exposed.

No ground. A knob and tube wiring system does not incorporate a ground. The ground wire on any circuit is the most important wire, as it is there for safety. Also, some electronic equipment requires a ground to operate correctly.

Switched neutrals. Electricians in the early 1900’s would switch the neutral feeding a ceiling light instead of the hot wire (today’s standard). Switching the neutral, would turn off the light, but live voltage potential would still be present at the fixture. Making a dangerous situation fora homeowner that is trying to change the light fixture.

Heat. Insulation becomes very brittle and breaks down when heated too much. Older light fixtures had no insulation in them to prevent overheating the knob and tube wiring in the boxes to which they were attached. These older light fixtures were usually not marked with a maximum wattage for light bulbs. Homeowners could be installing 100 watt bulbs in fixtures that were never meant to have such a high wattage bulb, the wiring above the ceiling fixture would break down, and sometimes the insulation would disintegrate.

Some insurance companies are not insuring homes with existing knob and tube wiring.

How to tell if I have knob and tube wiring?

A few things to look for:

  • Old porcelain knobs and joist sleeves in unfinished attic of basement.
  • Outlets throughout your home that have old two prong outlets int the baseboard.
  • Using a 3 prong tester, or voltage meter, test any and all three prong outlets around the house. If any come up with an “open ground” (means there is no ground), there is a good chance that wiring is tapped into the old knob and tube wiring.

Most homes have knob and tube wiring in the same locations

Homes that still have active knob and tube wiring seem to follow a similar format.

  • Front porch light and switch.
  • Front Entry light and switch(s).
  • Dining room light and switch.
  • Any three-way switches going up / down stairways and corresponding lights tied into these switches.
  • Additional 1st-floor wiring – Typically the older outlets still mounted in the baseboard. If the cellar is unfinished, getting to the outlets on the 1st  floor is quite simple, so these floors are typically already rewired.
  • 2nd floor wiring – Any older outlets in the baseboards, and sometimes lights and switches on this floor if there is a finished 3rd floor.
  • The 2nd floor (if there is a finished 3rd floor) is the hardest floor to rewire, as we have no unfinished space above or below.
  • If there is a finished 3rd floor, that is original to the house, this space often has some degree of knob and tube wiring left.

Careful rewiring techniques:

To rewire knob and tube, holes in walls and ceilings must be made to route new wiring around the house. Our electricians pride themselves in planning ahead, and making the fewest holes possible. Each of our electricians is highly skilled at fishing wires in the most proficient manner, and work as neatly and cleanly as possible. After the wires are fished, we will go ahead and patch all holes that we made.

One of our lead electricians James, leads all of our knob and tube wiring replacement jobs. He has been doing these jobs for years, and knows all the tricks of the trade, to do them with the least amount of damage as possible. For this reason, we are often booking out weeks or months for knob and tube replacement jobs. We limit ourselves to one job at a time, with our best rewire electrician leading all the jobs. We found that concentrating on one knob and tube wiring replacement job at time is the best system for us because it allows the jobs to be done with the most attention to detail.

We will use tarps and plastic to cover your floors and furniture, and move any furniture needed to do the knob and tube wiring replacement. It is a very dusty job, and our electricians pride themselves on leaving an area cleaner than it was.

While replacing knob and tube wiring, we are very conscience of keeping needed lights and outlets active if you are living there during the replacement. We have methods to make the jobs go as smoothly as possible, while not interfering with your life too much.

Fact: 90% of our customers are living in their home during the knob and tube replacement.

How much will replacing my knob and tube wiring cost?

We offer home owners with knob and tube wiring two options when it comes to pricing replacement:

Completely free in-home estimate. The KES team will come to your home and identify the active knob and tube wiring. These circuits at the panel will be shut off.  A walk through the home to identify all the lights and outlets that are no longer active. An estimate will be created off the findings, with an easy to understand “adjustments” section of the estimate. Meaning – If there is any modern wiring that is useful listed in the estimate (thought to be knob and tube wiring), you will be due a credit of X amount, and if any additional knob and tube wiring is found not listed on the estimate, it will be considered an extra at not more than X amount.

We use a completely transparent knob and tube replacement estimating style:

We use a “cost per point” method of estimating these jobs. A point is a switch, outlet, light, circuit from the panel, etc. There is no hourly charge for these knob and tube wiring replacement jobs. Let’s say the cost per point is $200.00 each, if you decide to add 2 outlets in one of the bedrooms, you know exactly what those additional outlets will cost. We like to be completely transparent when it comes to pricing.

The cost per point for homes can vary, based on the type of home. Some homes are much easier to fish new wiring, others are quite difficult and more time consuming.

Our knob and tube mapping service :

We will come to your home at an hourly rate and map out all the wiring kinds throughout the home, and identify them with a color code that is easy to understand. I will then base the estimate on this map (the map is yours to keep either way). If you elect us to do your knob and tube wiring replacement, we will credit you the amount you paid us for the mapping.

There is no variation in cost using the mapping method once we start the knob and tube wiring replacement. This method is for the owner who likes to know exactly how much the knob and tube wiring replacement will cost. Most homes take 2 electricians 2-5 hours to map properly.

Fact: 80% of our customers elect the free in-home estimate route.