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9.29 btus per HDD per sq ft too high for new system?

D107 Member Posts: 1,854
I question whether usage should be much lower given:

• 2156 sq ft 1950s house on LI, 47K heat loss

•5 yr old Buderus G115/3, riello 40 F3, Logamatic 2107 w normal curve, Buderus 50 gal indirect, new chimney liner, new Roth Tank. Two zones, run off T-stat.

•House kept at 70 (except two big rooms; porch is kept at 60; basement rads are off so real heat loss is much lower.)

• one elderly inhabitant

•Logamatic normal curve. house rarely gets below 65 at night.

• Nozzle .50 x 60W Delavan, runs smooth, no sooting.

Consistently uses 800 gal/yr. total heat and hw. Based on an average use of .33 gal/day during summer months for hot water only, I figured 122gal/yr for hw.

Combustion stats are ok, but stack temp never gets over 275 deg gross, which is ok by buderus current charts, but still pretty low according to many industry experts like George Lanthier.

I have seen reports by Wallies on this site with similar houses, older peerless boilers using 600 gallons a year.  Admittedly house is not airtight but it does have fiberglass insulation and when it was re-shingled years ago 3/8" of insulation board was installed.

Thermostat is fairly old honeywell chronotherm, anticipator set at .25, fairly close to the taco relay current (.18) which is considered the primary control here. When I'm in the house I sort of feel it comes on a bit too much but I can't quantify that. Perhaps t-stat night setback (70/65) and logamatic setback (72/63) should be lessened.

Any ideas? maybe new mix with biofuel burns less efficiently?


  • PeterNH
    PeterNH Member Posts: 88

    IMHO The wind must be blowing all the heat out of the house in a major way

  • D107
    D107 Member Posts: 1,854
    Doesn't feel drafty

    Funny, you don't really feel a draft there.

    There are some piping anomalies--main loop is a monoflo but after the 2nd rad (kitchen) a return was run back and the last rad in the line was fed directly from a split on same zone.

    I'm also thinking old 1950s convectors are not so efficient. And of course no FAI means boiler's sucking in cold air especially in the basement.

    But I guess lack of insulation is the more plausible culprit. Thanks.
  • Robert_25
    Robert_25 Member Posts: 530
    edited November 2011

    The big question is how much heat loss is due to infiltration? If the house has a lot of wind exposure, the losses due to infiltration can be significant. One thing is for sure, the heat is going somewhere...I did the math on my 100 year old house that gets blasted by wind and it came out to 7.15 btu's/HDD/Sq. ft.

    Also, you are making a big assumption on the daily fuel use for DHW. An indirect with uninsulated piping, no heat traps, and a small differential can really eat up some fuel.
  • PeterNH
    PeterNH Member Posts: 88

    I agree with Robert, the heat is going some where. It's clearly not going up the chimney when the boiler is running with those stack temps (jealous.)  Maybe an OVD might help for when it is off.

    Doesn't matter how inefficient the convectors are,  the heat is going somewhere.

    If it's not the wind in the house, then i would have a second look at the basement- heat loss and especially infiltration down there.  Between the pipes, the boiler, the chimny, the indirect -  a lot heat loss potential.

    Insulate the pipes with at least a half inch of something, add blankets to the indirect etc.

  • D107
    D107 Member Posts: 1,854
    rim joists

    Thanks again. I know the basement rim joists have some old fiberglass but are not sealed with foam like they should be.

    External Chimney is about 18ft; I can hold a piece of tissue paper up to the barometric damper and see the suction. Don't be too jealous of 275 degree stack temp--definitely conducive to liner condensatin'.....

    Also the combo of the attic fan louver--on top floor of this split level--with the pull of the attic vent above might be adding to the stack effect. No fireplace.

    And of course this smallest Buderus could find nets 64K vs 47K heat loss (actually lower since some big rooms are unheated) that's got to be good for 10-15% right there.
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