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What strategies are there to discover the inputs for manual J in an old house?

bobhoperises | Posted in General Questions on

I think everyone who ever owned this house (climate zone 2, 1950) had a vendetta against building codes.

I’m not doing a major remodel, but the furnace and ducts need to be replaced. I’d like to do the calculations myself and see where that directs me. The issue is these manuals need a lot of inputs, which I simply don’t have. Sure, I could put a little hole in the wall and try to figure out the amount of insulation in there, but I wouldn’t be surprised if every wall was built in a different decade. Blower door doesn’t seem especially useful unless I can do it several times, which by my calculations is infinity dollars.

So I think what I am looking for is some sort of book on doing the detective/forensic work to figure out just what exactly is going on with this building.  I don’t need perfection–this place will never, ever be perfect–but I would like to stay within a standard deviation instead of assuming wildly.

Oh, and virtually all contractors in my area are booked out for months, and charge at least double the national rate. Hooray for being a boomtown.

Does such a book exist?

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  1. Expert Member
    NICK KEENAN | | #1

    I don't think such a book could exist.

    Do you have a history of utility bills? One thing you could do is look at weather records and correlate usage to weather.

    1. bobhoperises | | #2

      I am maybe being overly specific. There's got to be a book aimed at homeowners of old homes that go over common and not-so-common issues in a way that doesn't constantly gloss over the details by telling you to ask a contractor. Have you met contractors? Thanks for responding.

      1. Expert Member
        NICK KEENAN | | #3

        I don't think you understand what a broad question you are asking. In some parts of the country an "old" house is from 1980, in other parts it could be 1680. What is the house made of? Wood, brick, stone, steel, adobe, sod?

        The reason contractors are the way they are is that they live in a world of uncertainty. Houses aren't like cars, stamped out on an assembly line. Every house is hand built, a product of its time and place and the men who built it. A house with any age has most certainly been modified over the years, again reflecting the time, place and people.

  2. Expert Member
    NICK KEENAN | | #4

    Here is a good general starting point:

    Until the early 20th century, people heated their houses with solid fuel -- firewood or coal -- and lit their houses with oil lamps or candles. Those houses were hot and smoky during the winter. They were built drafty so that there would be fresh air so the inhabitants wouldn't suffocate. Since they were so leaky there wasn't much point to insulation so there was little if any insulation in the walls and roof.

    The trend today is toward eliminating combustion at all inside the house, and the best new houses are practically hermetically sealed. New houses will have substantial insulation in the walls and roof.

    When trying to bring an old house up to modern standards, generally the most productive place to start is in air sealing. The best way to do that depends entirely on the construction of the house. The next stage is usually adding insulation. In general the roof is the most rewarding place to do that but again it depends on how the house is constructed.

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