The moment usually comes with a home inspector’s report, an insurance renewal letter, or an offhand comment from a neighbor who just went through a rewiring project. Suddenly you’re reading about “knob and tube wiring” and wondering whether your house is a fire waiting to happen. The honest answer isn’t a simple yes or no. The real question isn’t whether knob and tube wiring exists in your home. It’s whether the conditions that make it dangerous are present.
At Garneau Electric, we’re licensed in both New Hampshire and Massachusetts and serve homeowners throughout Windham and southern NH. We see knob and tube systems regularly in older homes across the region, and we’ve found that most homeowners carry the same misconception: that old wiring is only a problem if it visibly looks bad. That’s not how it works. Some of the most hazardous conditions are completely invisible without a professional inspection.
Here’s what you actually need to know.
What Knob & Tube Wiring Actually Is
Knob and tube wiring was the residential standard from roughly 1880 through the 1940s. The system runs separate hot and neutral conductors through open air, anchored to wood framing with white porcelain knobs and threaded through floor and ceiling joists inside ceramic tubes. That open-air design was intentional. The system was engineered to dissipate heat freely into surrounding air, not to be enclosed.
Two features set knob and tube apart from modern wiring in ways that matter today. First, these systems run on 60-amp service with no grounding conductor. Modern homes are built for 100 amps or more and require a hot, neutral, and ground in every circuit. Second, the cloth and rubber insulation on knob and tube wiring is rated for 60 degrees Celsius. Most modern fixtures and appliances expect wiring rated for 90 degrees. When old and new components are connected, that temperature mismatch creates an overheating risk at every junction.
When Knob & Tube Wiring Becomes a Safety Problem
Knob and tube wiring that’s intact, undisturbed, and running through open, uninsulated framing carries lower immediate risk than most homeowners assume. The danger escalates under specific conditions, and those conditions are common in southern New Hampshire’s older housing stock.
Insulation Contact
The single most common hazard in this region is blown-in or spray foam attic insulation added around knob and tube circuits. Because the system depends on open-air heat dissipation, surrounding it with insulation traps heat against the wires and the wood framing nearby. NEC Article 394, which governs concealed knob and tube wiring, is explicit on this point. Under NEC 2023, enforced statewide in New Hampshire as of July 1, 2025, concealed knob and tube wiring isn’t permissible within hollow spaces of walls, ceilings, or attics where the wiring is surrounded by loose, rolled, or foamed-in-place insulating material. If you added attic insulation in the last ten years, this is worth taking seriously.
Insulation Degradation
The cloth and rubber insulation on these wires has been heat-cycling for 70 to 100 years in most homes. Over that span, it becomes brittle, cracks, and can leave live conductors exposed inside walls and attic spaces where the damage isn’t visible from any outlet or fixture. A home that looks fine from the living room can have exposed conductors in the ceiling cavity above it.
Patchwork Modifications
This is the most common real-world danger we see when inspecting homes in Windham and surrounding communities. Decades of DIY repairs have left many older homes with knob and tube circuits spliced into later Romex or BX wiring, often without proper junction boxes. These hybrid systems create failure points that a visual check of outlets and switches can’t reveal. The splice might be tucked inside a wall cavity, behind a finished ceiling, or in a corner of an unfinished basement. The wiring looks updated from the panel side and active knob and tube from the other.
How to Tell If Your Home Has It
If your home was built before 1950, check the unfinished spaces first. Knob and tube wiring is identifiable by the white porcelain knobs anchoring individual wires to framing members and the ceramic tubes where wires pass through floor joists. Unfinished attics, basements, and crawl spaces are where it’s most visible. Individual wires running parallel through open framing (rather than a bundled cable jacket) are a strong indicator.
At the outlet level, two-prong outlets without a grounding slot throughout the home indicate an ungrounded electrical system, consistent with active knob and tube circuits. One detail many homeowners miss: a newer electrical panel doesn’t mean the knob and tube has been replaced. Many homes in southern New Hampshire have had their panels upgraded while the original branch circuits throughout the house remain unchanged. The panel feeds modern breakers; those breakers still connect to 80-year-old wiring behind the walls.
What It Means for Your Homeowners Insurance
Insurance is often what brings this issue to a head. Many insurers refuse to cover homes with active knob and tube wiring, or they exclude electrical-related claims from existing policies. Failing to disclose active knob and tube wiring when obtaining or renewing coverage can void the policy entirely if a claim is later filed.
In New Hampshire, insurance companies may require a written inspection report from a licensed electrician confirming the system’s condition before they’ll extend or renew a policy. That report needs to distinguish between active circuits still carrying current and inactive remnants that have been properly disconnected. This distinction matters enormously for insurance qualification and isn’t something a homeowner or general contractor can reliably make without electrical training. The NEC 2023 adoption, effective July 1, 2025, adds a code dimension as well: if your home has insulation-surrounded knob and tube circuits, the system doesn’t meet the current code standard, which factors into how insurers evaluate the property.
What Homeowners in Southern New Hampshire Should Do Next
The practical first step is a professional inspection by a licensed electrician who can assess whether your knob and tube circuits are active or inactive, document the condition in writing for insurance purposes, and identify which circuits need immediate attention and which don’t.
For homeowners who aren’t ready for a full whole-home rewire, phased rewiring is a reasonable middle path. Starting with kitchens, bathrooms, and attic circuits makes sense because these areas require grounded circuits under current code and represent the highest-risk zones for knob and tube wiring. GFCI protection requirements in wet areas, combined with the overloading risk from modern kitchen appliances on 60-amp circuits, make these the right places to start. A phased approach lets you address the most urgent safety and insurance concerns now while spreading the overall project cost over time.
Knob and tube wiring isn’t a reason to panic, but it is a reason to get an honest picture of what you’re working with. We serve Windham and surrounding communities throughout southern New Hampshire and offer free upfront estimates with no surprises. Financing options are available for homeowners managing the cost of rewiring. To find out where your home stands, give us a call at (978) 915-7860.