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Community and Q&A

Energy-Efficiency Upgrades to a Knob-and-Tube-Wired Home

diazswag | Posted in Energy Efficiency and Durability on

Daly City is the location to be exact. I pretty much feel like I spent a fortune buying a really crappy house (as far as building science goes)

The heating bill is astronomical. I went from an apartment building paying about $50 for all utilities a month, to about $500 per month on just electricity/gas in the winter months in this new house. What are the big bang for the bucks upgrades I should do?

There’s no insulation in the house. It’s using knob and tube wiring everywhere, so I’ve been hesitant to add insulation. However most contractors I’ve spoke to said knob and tube should be removed, and its safer, but for the price, and hassle, it’s better to just risk putting insulation over it, since it’s relatively safe, and most likely won’t have any issues.

Most big appliances are gas, like the furnace (80% efficiency 60k BTU), stove, laundry dryer. I recently replaced my water heater to a hybrid heat pump water heater since it had to be replaced anyway and there’s a rebate in my area currently. Not sure if I made the right decision because I realize electricity is one of the highest in the nation here in this area.

Windows are mostly double pane windows, not sure what brand. But it’s probably not a super high end brand. There’s a few windows that are still those aluminum frame, single pane, but just a few.

Crawl space is also vented, not sealed/encapsulated, but not sure if it warrants sealing in my area’s climate.

I may be considering solar panels in the near future.

Any advice would be appreciated! Thanks

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  1. walta100 | | #1

    How long will you own this house?

    If you like most people are gone in 6 years the only thing you are likely to get back from saving in 6 years is caulking and air sealing.

    Put a fan in your window and use incense sticks to find the air leaks and fill them with caulk.

    Seems to me knob and tube wiring must be 70 years old and to me is past its useful life and is most likely under sized for the way we use electricity today. It is only a matter of time before you find it necessary to upgrade the system and the sooner you do it the less likely you are to die from fire or electrocution.

    I think anyone that says “it’s relatively safe, and most likely won’t have any issues.” Only cares about making a sale and should be shown the door as they clearly willing to risk killing you to make a dollar illegally.


  2. stevedavis | | #2

    Hello fellow bay area recent home buyer! I'm in the same boat down here in Santa Cruz. No easy fixes especially if you aren't planning on sticking around as Walta noted. My situation sounds very similar to yours. I'm not sure how big your house is but mine is just under 1300SF and we were having about $200/month energy bills. Laughable to the rest of the country but there's definitely room for improvement here in CA - not to mention the comfort differences.

    We decided to just bite the bullet. Here's what I did:
    1. enclose the crawlspace. I did this myself and it sucked a lot but is cheap to do. Winter is fantastic. Summer requires a dehumidifer.
    2. Seal up the duct work. All of mine is located in the crawlspace and attic so its relatively easy to do. Went from 25% leakage to 5%.
    3. Removed all the old attic insulation. Cost 1k.
    4. Air sealed the attic. Easy without insulation. DIY.
    5. Reinsulate the attic. 1.5k in materials. DIY labor.
    6. Remove all the interior sheetrock. DIY labor.
    7. Airseal like crazy. DIY labor.
    8. Full rewire- I'm currently in the middle of this. Peace of mind. But it costs us 25k.
    9. Reinsulate the walls - $800 in materials. DIY labor.
    10. New drywall - Costs us 9k. We are retexturing all the interior walls that remain to be smooth however to match the new drywall on exterior walls.

    Hope that gives you some help. That's my bite the bullet approach.

  3. user-6184358 | | #3

    Hi, Get rid of the knob & tube antique electrical system. Does you insurance company know it is knob & tube? You won't be allowed to install solar with the old meter and service entrance.
    Then air seal the attic plane and insulate the attic, as a minimum -Follow what Steve is doing. Bite the bullet and make the next buyer happy (and poor)

  4. diazswag | | #4

    Thank you everyone for taking the time and effort for all the feedback!

    Steve, I commend you for having the chops to do all that yourself! I'm not a handy guy, I'm a computer geek with handy fingers but pretty out of shape everywhere else of my body to be doing all that work! My brain kind of works OK though, so I'm trying to understand the science behind it and hopefully I can find a contractor to do everything right!

    One thing I'm trying to understand more about is the crawlspace building science, so I can figure out what to do with my crawl space. My understanding is moisture forming on the surfaces (on the underside of the floor aka ceiling of crawl space) of the house is the concern for crawl spaces. Moisture forming on surfaces happen when surface is cold, and moisture in the air condenses when touching the surface.

    Again, I'm in Daly City, and visited maybe 50 open houses in my neighborhood. None of which have sealed crawl spaces. Our crawl spaces are about 3' high above dirt floor with red wood joists and subfloor above. I understand most places in the country, the weather pattern is different (and extreme than where I am), and a lot of the building science is more or less catered to those areas. Could it be possible that in my area, there's simply no moisture issue? Could it be possible that there's simply never a condition where water is condensing onto the ceiling of the crawl space? For water to build up in vented crawl space, that would mean the temperature in the crawl space is equal to the dew point (or humidity in the crawl space reaches 100%), but I don't think this ever happens. If it's true that my crawl space never hits dew point temperature, or gets to 100% RH, is there any point to encapsulate the crawl space?

    This would help me decide whether it's sufficient to just use fiberglass bats between joists on top of crawl space.

    Does my reasoning / logic make sense?

    Thanks in advance

    1. stevedavis | | #17

      I'd suggest sticking a temperature/humidity sensor in your crawlspace so you can better assess whats happening down there. You are right that the sealed-crawlspace 'craze' is really more focused in other parts of the country (the south) were things are much more humid in the summer (dewpoints in the 70s vs low-mid 60s here). I think the amount of time and resources spent to seal off a crawlspace in our climate is debatable but I wanted to take a best practices approach.

      One thing to note is that it goes beyond just condensation and 100% relative humidity. You want to ensure you keep the crawlspace at around 60% of less relative humidty. Above this level, nasty things like mold start to grow and will eventually make its way into your home.

      So in summary - necessary? debatable. But if you want best practices than I'd say do it.

      1. stevedavis | | #20

        One comment that I haven't seen yet is in regard to radon. If you do decide to seal your crawlspace, you should check for radon afterwards. We live in a "level 2" zone. So its not a guarentee that you have radon but you very well might. My sealing up the crawlspace, you'll end up with more radon in the house. You'll have to install a fan to depressurize and blow it out. I found that we did have elevated levels and had to install a mitigation system.

    2. scottohara | | #18

      I live and work in the East Bay. Most of our projects include a sealed crawlspace because we like to put the equipment and ducts down there, especially with the amount of room you have. Seal the crawl, close the vents and insulate the cripple walls if you have them and that space becomes pretty close to conditioned space in our climate, enough so that you can plug them in as conditioned in load calcs.

      Your also cutting down on a big source of air flow potential in the house. A lot of those old houses have diagonal 1x floor sheathing that is pretty much impossible to air seal.

      We've never insulated over Knob and tube for all the reasons previously stated.


  5. user-6184358 | | #5

    I forgot to mention a seismic retrofit on the crawl space stem walls. They tend to collapse in earthquakes if not braced properly
    Oh yea the CA Earthquake authority has a discount for properly braced stem walls.

  6. CLEAResultBoulder | | #6

    I am an Energy Advisor for the BayREN Home+ Energy Advising Service. We offer free and unlimited Energy Advising for any Homeowner, Property Owner, or Tenant of a Single Family Home or a MultiFamily building structure (think townhouses, condos, duplexes, etc) up to four homes. There are other factors, but as long as you live in one of the 9 counties that surrounds the Bay Area, and your home was built before 2016, our program services would apply.

    I (our program can help you or any other resident in the Bay Area with PG&E as their Electric and/or Gas provider. (For other readers/contractors, check your own state, county, city to see if programs like my own exist in your own area).

    First, I hope this does not get tagged as spam, because I'm 100% certain we can help you, especially if you are a Do-It-Yourself'r, data-driven nerd, or looking for unbiased information or education. Our program does have incentives for upgrades related to a homes Thermal Envelope, HVAC upgrades, Electrification, Water Heater Replacement, Home Performance with Energy Star, Energy Audits, Home Energy Scores, Etc.

    Your experiences are similar, if not identical, to symptoms other homeowners experience. Your description is 'by the book' for bay-area single-family homes. Your behaviors, gas/electric usage, the configuration of your HVAC (heating/cooling) system, capabilities for Air Sealing (to retain energy), capabilities for Insulation (to sustain temperature), possibly roof ventilation or other cost-effective upgrades may be available to help your home perform as a machine while increasing your comfort, efficiency, and safety (think Indoor Air Quality). <--That is the elevator pitch I guess.

    Look us up. We are absolutely slammed, but I find it pretty cool you are coming into GBA for some advice. GBA is a SOLID resource and I'm interested to see what others recommend in here.

    Based on our recommendations, I'd suggest you consider the following possible upgrades.

    Starting from the top down

    1. Natural Static Roof Ventilation - Use equally divided eve/soffit ventilation and peak ventilation. No Mechanical Ventilation unless recommended for wildfire danger zones. (we have a formula recommendation for this)

    2. Attic Air Sealing and Insulation - In your area, R30 or R38 will be code. Our program requires R44 in addition to Air Sealing. If you don't use one of our participating contractors or you do work yourself, I'd highly recommend you have someone first conduct a Blower Door test and then again when you finish Air Sealing to determine if you need Whole House Mechanical Ventilation, which Greatly improves and controls Indoor Air Quality.

    2.5. If your ductwork is located in your attic and if you experience differentials in how your home heats or cools (one register blows out tons of air and in another part of your house, one register barely gets any air), once you remove your Knob and Tube, we would recommend replacing/modifying your ductwork to match your existing system or prepare for a new HVAC forced air system Air Handler. This all depends on the shape of your existing system and if you have any issues with how your system performs.

    3. Wall Air Sealing - Insulation only you want to repaint your interior walls soon. Next time you do paint, that would be a good time for Wall Insulation. Otherwise, focus on installing insulation on the Southwest facing walls that may feel warm to the touch and negatively impact your environment. Northeast facing walls that may feel cold to the touch and negatively impact your environment. If you have the funds and again you plan to repaint the interior of your external walls, then go for Blow-In Dense Pack Loose Fill as your material. Basically any loose fill will do, it's up to you and your own research.

    4. Whole House Air Sealing - This mean you or a contractor goes around the home and closes up any external holes or gaps on the exterior of your home and seals them up. Air Sealing retains energy.

    The analogy we use: When you blow up a balloon and tie it off, the balloon retains the energy. If you place the balloon under a jacket, a piece of fiberglass insulation, or a blanket, those Air Permeable materials help to Sustain the temperature inside the balloon because they Insulate the object. As soon as you grab the balloon and pop it, the energy escapes, right through the insulation and into the exterior environment.

    That would be the path I would set you on. You might also consider starting with a Comprehensive Energy Audit (they take 4-6 hours to complete), but free estimates or DIY research can go a very long way. Your experiences and behavior play a huge part. But typically there are several cost-effective upgrades available for homeowners to consider first.

    We also don't see much benefit from Insulating Floors. Instead we recommend Crawlspace Encapsulation to 100% or 80/20% based on what your local code may allow. Crawlspace Encapsulation allows a home to 'take advantage' of earth's temperature and can greatly improve indoor air quality and seasonal comfort.

    We would leave Windows, Doors, Fenestrations to the last option as they are scientifically proven to save between 5% and 7% of energy loss. Society and Marketing will advertise homeowners can save 25% or more. For the cost of replacing all your windows or doors, you may instead be able to replace only a few important ones, weatherseal the rest of them, air seal their frames, air seal your house, insulate your attic, insulate your walls, seal or modify your existing ductwork, and probably have funds left over.

    Good luck.

    Whoo hoo. It's late!

    1. diazswag | | #22

      Just FYI, I reached out to CLEAResult, and seems like they don't have a program on behalf of PG&E. Here's what I got back.

      Thank you for reaching out to CLEAResult.

      "Unfortunately, we do not currently implement a residential homes program on behalf of PG&E. However, here is a link to their website where you can find more information: "

      1. diazswag | | #23

        Reaching out to now! That's probably who you meant!

  7. severaltypesofnerd | | #7

    There are a variety of home performance contractors and non-profits working in SF that can look and help you prioritize (BayREN among them).

    As for your knob & tube or k&t. It's fine. Really.
    It was installed by guild trained electricians to high standards and will outlast both modern wire and the house. It's legal in California to insulate over it, and its an absolute myth that there is any sort of "heat problem" with K&T. Fake news.

    There are a few k&t problems. You want to peel off the high wattage laundry, small appliance, dishwasher, disposal and (god forbid) space heaters onto new circuits. Get everything off fuses, which ARE a problem, and onto breakers, AFCI at that. Just for good measure, use 15A breakers rather than the 20 the wire is good for.

    Then be happy with the K&T.

    With modern LED lights the load is far less.
    The old copper wire still carries the original design load.
    The "heat" thing is a myth.

    1. walta100 | | #11

      From a safety point of view the K &T wiring is a hazard in that it has no ground wire run this is a very important safety requirement add to the electrical code in the 1960s the metal case of most appliances are connected to this ground this ground will carry away any voltage should a fault occur in the appliance without the ground touching the appliance with a fault could be a shocking experience.

      The electrical insulation on the K&T wiring I have seen looks pretty sad after all its years of service and not something I would trust with my life by touching. Most every joint wrapped in cloth tape that is 70 to 90 years old and most tape is not sticky after 10 years.

      If you still have K&T wiring you are also likely to still have fuses in your panel. Fuses are a hazard because the 15 amp fuse blows a few times someone decides to replace it with a 20 or 30 amp fuse the fuse may never blow again but the wires in the wall may one day get hot enough to start a fire. (how sure can you be correct fuses when you bought the house) The copper connections in the old panel are not a bright and shiny after 70 years of service and corroded contacts get hot and start fires.

      Back when K&T wiring was installed people did not need or want much electricity for a few lights fans the fancy new wringer washing machine was the big load with a 1/3 horse motor. So the wires were skinny and far apart the service is likely only 60 amps.

      The National Electrical Code decreed in 1987 that it would not permit insulation contact with knob and tube wiring systems, though some jurisdictions still allow it if the wiring is in good condition. I doubt any insulation manufactures instructions that would allow it even if your local government would permit it.


    2. Expert Member
      BILL WICHERS | | #19

      There is no guarantee that knob and tube wiring was installed well. I have seen plenty of crummy installs. While it's true that the ceramic insulators don't degrade, the old rubber and braid insulation on the wire itself certainly does, as does the tape that was typically used on splices. It WILL NOT outlast modern wiring, only the ceramic parts will. For all practical purposes, modern THHN/NM-B wire will last the life of the home, and the newer insulating materials are far, far safer and more stable than the old natural rubber and cotton braid that used to be used.

      Fuses being a problem IS a myth. The fact is that fuses are more reliable than circuit breakers in terms of their ability to actually clear a fault. Circuit breakers can and do age, and are supposed to be cycled at least once per year (even though no one does that), fuses don't have any of those issues. In a very big fault, fuses are nearly guaranteed to function and open the circuit, breakers sometimes don't. I always spec fuses in the large mains of the commerical projects I work on at work, and the reason is because they are safer and more reliable in those applications. The primary advantage of circuit breakers is convenience, not increased safety.

      The "heat" thing is not a myth. The old wire was a 60*C wire, if that. The newer wire is 90*C rated (even though you have to size NM-B from the 60*C table). Granted, this is only really a problem if you are heavily loading your circuits, which you should try to avoid, but even then, modern wiring holds up much better if running hot compared to the old stuff.

      I would replace the old wiring. One of the big weak spots in knob and tube systems was taps and splices, and many of the taps to fixtures/devices was made with type R cable, or similar, and that stuff most certainly IS a problem -- the insulation gets old and crumbly, any water gets on it and it's done (short circuit), etc. I wouldn't risk it.

      BTW, in my opinion as an EE, and in the opinion of nearly every electrician, AFCIs are of dubious value in terms of increased safety. I use them where required by code, but I'm not a fan of them. They are too prone to false trips, and they don't offer much additional safety beyond their ability to trip on a particular type of fault that is exceedingly rare in practice.


      1. diazswag | | #21

        I appreciate the electrician's perspective on K&T! Cheers

  8. diazswag | | #8

    Bryce what you said makes my wallet really happy! We don’t have fuses but the AFCI and peeling high load appliances off to new circuits is a good call. I might need to upgrade my panel (currently 120A) anyway so this is great! Looking at your previous messages sounds like you’re in Berkeley which is similar weather to where I am. It’s a lot foggier and overcast over on this side of the bay (and I’m right next to the beach). Thanks, and Nice to meet you!

    ClearResult, thanks for ALL that great info! I’ll sign up and get an energy audit. I’ve done a blower test before and my house is something ridiculous like 14 ACH … I actually paid for the energy audit and was told to start off with insulation, so now we’re at the deciding of how to deal with K&T.

    1. severaltypesofnerd | | #9

      Never start with insulation. Always start with air sealing.

      Old houses can be upset in terms of moisture by insulation, among other things.
      Insulating in general makes future renovations harder (try repairing electrical if you have to first swim in cellulose insulation).

      Whoever told you to start with insulation was not giving experienced advice.

      What kind of roof? Perhaps re-roofing with 4" of solid foam ABOVE the roof deck would leave your interior pristine, but give a cap to all the heat going straight up.

      Again: air sealing first or you're wasting your insulation dollars.

      1. diazswag | | #10

        100% on the air sealing, and insulating as a LAST step after everything is finalized.

        Interesting suggestion about the 4" foam on TOP of roof deck! Regarding the roof type, I know its shingle asphalt. It has many faces. Googling roof types, it seems more like a hip roof, with a flat part on top. It's definitely not a gable. It is a bit worn in some areas, and the solar panel guys told me I'd need to patch up certain areas for them to put solar on it, so something worth considering now would be to replace the roof, and put 4" foam.

        How would the performance of the 4" foam be, versus something like the blown-in cellulose? All the insulation companies recommended blown-in cellulose, but that seems like a mess, and would be hard to do any work in the attic if needed, like you already mentioned.

        1. severaltypesofnerd | | #12

          The calculated value of the foam might not be great,
          but it avoids thermal bridging of the wood, and the likely massive air leaks inherent in retrofit attic insulation. Read up on the topic, it's a big one.

          Tradeoffs are global warming emissions vs. carbon capture of cellulose. Cost. And the greater surface area of the roof compared to the attic floor (more area to insulate).

          Post air photo links.

          1. diazswag | | #14

            Thanks, I'll read into it. Here's a picture of roof from google maps.

          2. diazswag | | #15

            Here's an article by Martin Holladay about rigid foam over roof sheathing.
            The article also talks about adding extra batt insulation inside on the cavities between the rafters.

            Very clean design. I wonder if it's effective, and I wonder if there's even anyone in my area who can even pull this off without it being shoddy. If I'm redoing my roof anyway, I wonder how much something like this would cost versus blown-in cellulose.

            Would that insulation model work with a vented attic or would the science of it require closing up the vents? Not super well versed with the attic science, but common sense tells me they should be vented if the insulation is on TOP of the roof sheathing. To protect the warm air from simply going out the vent (and cold air from coming in through the vent). Seems like detailed care would be required to keep soffit areas (or other areas that could get really cold) to be insulated well, so warm air in the attic doesn't condense there.

    2. Expert Member
      Akos | | #13

      The problem with knob and tube isn't generally the older install, but modifications down the road. The houses I've replaced K&T on always had some hacked on additions or modification that at best looked sketchy, some shown clear signs of overheating.

      Around me, it is very hard to get insurance on a house with K&T, so keeping it is not an option.

  9. diazswag | | #16

    GBA community is awesome. I really appreciate all the perspectives regarding K&T wiring.

  10. JC72 | | #24

    Attached a lightning rod onto the roof and then go on a two-week vacation.

    [Sarcasm, sort of, but not really]

  11. paul_wiedefeld | | #25

    Have you used Dana's heat loss calculation method yet?

    You're in an ideal location for a heat pump considering how warm the winters are (annual COP probably >4), which would be a major emissions reduction. Sizing is key for this, so start with Dana's calcs. I suspect the furnace is massively oversized. Modulating heat pumps (>1 speed) get more efficient as their RPM decreases, so if you make air sealing/insulation improvements post heat pump installation you'll both reduce the total energy required and make the equipment more efficient. Solar is your best bet to bring down your $/kwh and a no-brainer in California. With financing, it can cost nothing up front.

    1. diazswag | | #26

      Yeah great advice! I'm looking into solar; the thing is my roof is not in the ideal condition (nor is it too old to just replace). The solar guys said theres about 10 years left of roof life, so it's still pretty good, but there are worn patches that I have to reinforce with another layer of shingles or something. All the work will cost about $10k.
      I'm considering maybe replacing it and using the "top of the roof" rigid board insulation method (versus blown in cellulose under the roof). I'll have to see how the pricing settles down to for all these different methods!

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