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  1. #14
    Join Date
    Jan 2004
    Quote Originally Posted by bobRitchie View Post

    I have a 1700 ft^2 1960's ranch in San Jose with ceiling insulation
    and all double pane windows, but nothing in the walls, a living room
    with no ceiling insulation. It does get down to the lower 30's here
    on winter mornings. And it will take my 80% 100,000 BTU trane furnace
    a good hour to raise the temp 7 degrees on those winter mornings.
    Considering that your design temp is around 29*. That would be considered a quick recovery.
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  2. #15
    Join Date
    May 2008
    East Bay, Northern California

    Bob Richie


    Thanks for your thoughts. Given how close you are to me, your experience is probably the most relevant. I'm still going to ask the guy for a load calc, but now I am not as suspicious that he's off base.

    I doubt that there is much insulation in the walls of my house, given that the walls are from 1922. I'm doing a total bathroom remodel right now and when the contractor opened up the walls, he found no insulation. It would be impossible to insulate the walls of the house without causing major disruption. They are all lath and plaster. I think they'd have to be torn down and replaced with sheetrock. Think of what a mess that would be.

    Also, my crawlspace is, as you guessed, highly ventilated. It has at least 3 or 3 1/2 feet of clearance and large vents.

    Thanks again for your input.

  3. #16

    Design temperature

    A design temp of 29 sounds about right for San Jose.
    And it Never gets colder than that. But it often gets
    close to that. At least in th AM. By afternoon it
    will often be in the 60's even starting from 30's.

    I imagine in other areas where the design temp might
    be 10 or something, it rarely gets that cold, but sometimes
    gets colder.

  4. #17
    Join Date
    Jan 2004
    7°F in an hour is a fairly quick recover at design temp. And not needed. A good thermostat will bring the system on a little earlier to get to temp on or near design days.

    I keep my own oil furnace down fired. It takes it a while to recover. But saves a lot on fuel.

    An over sized 2, or 3 stage furnace uses more fuel the a proper sized single stage furnace.
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    How many times must one fix something before it is fixed?

  5. #18

    2 stage furnace

    Been there,

    You had mentioned that on another thread, and that was
    a surprise to me. If what you say is true, that my two stage
    furnace is actually more efficient in the second stage, I hate
    my thermostat that allows for much of recovery to occur in stage 1.
    I'm again tempted to build my own thermostat that would do recovery
    in stage 2, and the rest of the time run stage 1.

    I tried to google that, and all I quickly found was a Berkeley lab study:

    They are saying that two stage furnaces save energy only because
    the blower can run on a lower setting in low. But they clearly
    believe the thermal efficiency of each stage is very similiar.

    Do you have any reference that would back up your claim that despite
    the ratings, the second stage is actually more efficient? Maybe this
    is true of 90+ units, not a 80% eff. like mine?

  6. #19
    Join Date
    Jan 2004
    Just the steady state combustion test I have done on 2 stage units.
    And others on this board have seen the same.

    Some 2 stage only lose a little. Others lose a lot.
    Too many companies don't even bother to set up the stages. They just turn them on, and leave.

    2 stage furnaces are for comfort, not savings.

    If you want to recover with second stage. Disable Adaptive Recovery.

    PS: If your recovering 7* in one hour in first stage when its at outdoor design temp (29* in your case), your grossly over sized. And using more gas then you need to.
    Last edited by beenthere; 07-24-2008 at 11:18 PM. Reason: added PS:
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    How many times must one fix something before it is fixed?

  7. #20


    For the first forty minutes or so is in second stage.
    Then when the supposed temperature gets within
    2 degrees of set, which for my case more like 3-4
    it goes down to first stage. I don't have adaptive
    recovery on, it just starts abruptly at the set time.
    But I wish it would finish the job before throttling down.

    Its possible that the place that gave us the atom bomb,
    can't figure out two stage furnaces. Having worked with
    physicists for years, I still don't know how the heck they
    pulled off the A and H bombs.

    Been There, given the number of posts you make to this
    board, I have to guess you are retired and this is your
    hobby? Or just business is slow?

  8. #21
    Join Date
    Jan 2004
    I work out of my house, (living room is the office, and the basement is shop, storage) and have access from most areas I'm in.
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    How many times must one fix something before it is fixed?

  9. #22
    Join Date
    Jul 2005

    insulation option

    Can they blow in insulation from the extiorer of the house into the walls?

    They do that a lot up here in the boston area with good results.

  10. #23

    Wall insulation

    When I added cellulose insulation to the attic a few years ago,
    I had them do a small section of wall as a test.

    It was not a success for two reasons. Number one they did a lousy
    job of patching the huge holes they made in my rough wood cedar
    siding. Number two many of the drywall nails popped on the interior,
    and I had to screw the drywall down more securely, patch and paint.

    So I would basically have to re-side the house, and screw down all
    the drywall. And in this climate the natural wood siding I have, which
    is 40 years old, in perfect condition. Which will easily last another
    60. One thing that protects it and keeps summer temps down is I
    have three feet of overhang all around the house.

    This is an extremely mild climate. I forget the numbers but I think
    its something like one fourth the heating degree days you have in
    Boston. I spend something like $600 a year for gas for heat. From
    HVAC-calc I figure I'd say something like 15% for insulating the walls.
    The return is just not there.

    Actually I probably have more heat loss associated with my crawlspace.
    Although I think HVAC-calc overestimates it, because it assumes the
    crawlspace and ducts in it are exposed fully to the outdoor ambient.
    While we can have temps in the 30's during the night in the winter
    the daytime temps for the same day are often in the 60's.
    Here we have crawlspaces with 4x14 vents every foot. Just closing
    off the vents could save some. But during the rainy season there some
    moisture can accumulate down there. That's from seepage during extremely
    heavy rains that happens maybe once year. Unlike the humid east, natural crawspace ventilation here actually is a very effective of drying out
    a crawlspace.

  11. #24
    Join Date
    Jan 2004
    Around here. When they blow insulation in a wall, they do it from the inside.
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    How many times must one fix something before it is fixed?

  12. #25
    Join Date
    Apr 2008
    Alberta Canada

    I would say

    Why would you cut holes in a wooden shakes instead of drywall. Maybe you should leave that stuff to the people who kow howto do things properly. Then you would see positive results. In stead I think you are beating a dead horse with the way you are approaching it.
    Do it right the first time.

  13. #26

    I didn't cut the holes in the siding.

    The contractor I hired did. Who was rated highly on
    Angies List, but I will not name. He was pushing to sell
    me wall insulation in addition to the attic insulation I wanted.

    I was skeptical, that's why I only allowed them to do
    it in a small area.

    If energy prices continue to soar, maybe someday I'll consider getting
    some insulation in from the inside. However I would want to screw
    the drywall down better. And my drywall all has textured patterns
    that aren't super easy to match.

    Most of my DIY projects in my lifetime have been to correct problems
    done by contractors that I've hired. I had a painter who power
    washed my overhangs before painting them. He injected tons of water,
    that caused the new paint he put on to bubble. I ended up scraping
    and painting them all myself.

    In the HVAC arena 6 years ago I had all my ducts replaced suposedly
    to be large enough for A/C which they weren't originally. Well the
    return they put in was one severely kinked 16" flex duct (90 degrees
    in no space at all). For a
    four ton system. I got rid of the kink by building my own sheet
    metal box in the wall. But I still have only a 16" main return duct. My
    static is about 0.8 inch. So I'm moving about 1400 CFM, which is
    not the desired 1600. But I figure that I'm only losing about
    5-10% efficiency.

    Surprisingly I have never sued a contractor. But I have waved a hammer
    at a gang of Asian workers who were making a mess out of a $30,000
    deck rebuild job.

    I have never lived in a house that I didn't discover serious electrical
    problems in. Here the worst was the refrigerator plug had the ground
    of the receptacle connected to the neutral. So if the neutral had ever
    openned up, the stainless steel fridge with big metal handles, which
    you often touch with wet hands would have be live. I actually
    lived here for a couple of years before finding that. This house was
    built in the brief era where there was two conductor romex without
    ground. And of course they replace receptacles with three prongers.
    But I think because the fridge has fancy electronic controls it was
    going nuts with an open ground. So they just shorted to neutral.

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