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D.O.E. or I.B.R ??

ScottMP Member Posts: 5,884
with the Mod/Cons is IBR even relavent anymore ?
How much pick-up and boiler loss is there ?

I've always done IBR just to be save but I am being told I'm wrong. Not the first time but this time its not my wife. :)


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  • Mike T., Swampeast MO


    1) You have calculated loss using Manual-J


    2) The mod-con is installed in a system where you can reasonably expect return temps of 140F or below the vast majority of the time


    3) The mod-con works with either well-adjusted outdoor reset or indoor reset


    Not only would I suggest that I=B=R ratings loose relevance, I believe it very safe to choose a mod-con based on the best match between boiler input and heat loss.

    Do though be wary of old systems with lots of large, uninsulated iron/steel piping in an unheated basement. While there will be almost no "pickup factor" once the well-adjusted mod-con is doing its job, those pipes can put out a LOT of heat. Unless you nicely insulate the piping, I believe it best to add the basement to the heat loss calculation as heated space with the ground floor over conditioned space.
  • ScottMP
    ScottMP Member Posts: 5,884
  • Mitch_4
    Mitch_4 Member Posts: 955
    so far

    I ahve found that heat loss calculations have an average of 40% "fudge factor"

    I usually go on input for ANYTHING in the high efficiency catagory modulating or not. not bit yet in 2 years
  • Steve Ebels_3
    Steve Ebels_3 Member Posts: 1,291
    All of the above

    As far a mod con boilers go, my humble opinion is that IBR rating are irrelevant and meaningless. I go with DOE or less even on Cast iron systems running with ODR. (pretty much eliminates the pickup factor)

    One of the main reasons I choose to disregard the IBR rating and in many cases the DOE also is that heat loss calcs if done correctly will almost always oversize the boiler or furnace. They just plain have a lot of margin built in especially if you go by your actual low temperature instead of the ASHRAE listed temp for a given area. Example, we routinely see 15-20 below every winter but ASHRAE says design for -6* here. I have a gut feeling that all these numbers and ratings have been developed by folks whose main goal and concern in life is covering their butt in the worst possible case, like a once in a hundred year event or bringing a house up from 45 to 70* during exterior design conditions. Then you might possibly need all of the DOE rating and better have the emitters to go along with the boiler.

    I'll give a couple real world examples.

    #1 3,800 sq ft single story ranch with normal 10 year old construction and average insulation. 60,000 BTU condensing furnace (input)

    #2 5,100 sq ft older house with elderly occupants (think 76*+ indoor) heated with a Cast iron boiler carrying an input rating of 103,000. Does the domestic too.

    #3. Remember my house from Hades a while back? The heat loss for that place was calc'd at 147,000. The boiler would do more than that but during the first winter it heated almost perfectly with only 45-50,000 bru's worth of attached radiation.

    I know that an attitude of cautiousness is natural with folks who are advanced in years but we'll forgive you this time and we still love you :) A tip of my hat to Betsy, that was a sweet birthday present!
  • Mitch_4
    Mitch_4 Member Posts: 955
    I can add

    My own real world.

    My house 2100sq.ft 4 lvl side split. Heat loss calced at 52k @ design, real world at 23° BELOW design temp for 2 weeks, 70% run time MAX (42 minutes) I know because I heard the weather and was up in case I needed to fire up the woodstove...after it did that inthe middle of th night with the wind HOWLING, I went to bed.

    So..at 23° below design temp, my ACTUAL heat loss is about 40,000.(93% 60,000 btu unit installed (FA by the way)) It has been replaced with a 2 stage.

    There is a HUGE fudge factor in heat loss calcs
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