Knob and tube wiring in Massachusetts
It was common in houses built before the 1940s. It matters now because it can stop Mass Save insulation work and, through that, a heat pump.
- Checked: November 3, 2026
What it is
Knob and tube is an early wiring method: single wires run through the framing on ceramic knobs and through ceramic tubes. The City of Boston describes it as two wires, a hot and a neutral, with no ground wire, and says the protective coverings can break down over time and become a fire hazard.
Many houses were later rewired but still have old knob and tube left in the walls or basement. That leftover wiring is often inactive.
How to spot it
- The house was built before about 1950 and has two-prong outlets in some rooms.
- In the basement or attic you can see wires running along ceramic knobs on the joists, or through ceramic tubes.
- Cloth-covered wires, or a fuse box instead of breakers.
Look, but do not touch or open walls. Only an electrician can tell whether it is live or inactive.
Why it comes up with insulation and heat pumps
Eversource says the up-front Mass Save barrier incentive covers projects such as removal of knob and tube wiring that must be completed before any approved insulation upgrades can be installed. Mass Save then asks that the weatherization recommended in your Home Energy Assessment be finished before the enhanced heat pump rebate. So old wiring can hold up the whole chain. The Mass Save guide has the dates and links.
What can happen next. An electrician looks at the house, tells you whether the old wiring is live or inactive, and quotes either removal, a partial rewire or a full rewire with a new service. We do not quote. The electrician does, after seeing the house.
What it costs
Cost depends on the size of the house, access and what is behind the plaster, so the electrician quotes after seeing it. For scale: at least 558 Boston one-to-four-family permits from 2025-11-01 to 2026-11-02 mention a rewire or similar work, with a median declared value of $15,000. That is the figure on the permit form, not a price. See the permit data.
Permits
In Boston, a homeowner cannot pull the electrical permit. The City says you must hire a licensed contractor to apply for the permit and complete the work.
Questions to ask the electrician
- Is the knob and tube live, or inactive? How do you know?
- Is the work needed for my Mass Save job, and what does the assessor need to see after?
- Will the service be upgraded in the same visit, and who schedules the utility?
- Please show me your Massachusetts license number, and I will check it on the state's public license lookup.
Common questions
Can I insulate if the old wiring is inactive?
The City of Boston says you can still proceed with insulation as long as the knob and tube system is inactive. An electrician has to confirm whether yours is live or inactive.
Can I rewire the house myself?
In Boston, the City says a homeowner must hire a licensed contractor to apply for the electrical permit and complete the work. Other towns have their own rules, so check with your building department.
Does Mass Save pay for it?
Mass Save and Eversource describe up-front money for removing knob and tube that blocks insulation, for homes that pass income verification. Whether you qualify is decided by Mass Save and your utility.
Send two photos, get a price.
A photo of the panel and one of the boiler or furnace is enough to start. We look at it and get back to you.
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