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looking for article that explains condensing boilers

Joseph_4 Member Posts: 233
Hi. Does anyone have a link or article that explains how condensing boilers work and how they save money because they are more efficient?




  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Save You Some Time

    Pulls the latent heat out of the flue gases that is generally wasted thru the venting system. Need return water temps below the dew point (generally 134 degree water temp) to condense. Modulates its btu ouput as well as water temperature output based on the out-door temp based on the installers programing.

    In a nutshell that's where the savings comes from. You should also be researching low temperature hydronics. The boiler is the mother, hydronic system side the father. The savings is it's offspring. Without knowing how they all work together to make that offspring you only looking at 1/2 of the picture. Suggest you visit the store here and pick up Modern Hydronics Third Edition.,
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Tim McElwain
    Tim McElwain Member Posts: 4,506
    I certainly

    cannot compare with Mark Eatherton, Carol Fey, Siggy or others who are certainly the tops in their field and excellent writers of manuals and instructions.

    I will however if you contact me send you for free what I use as an introduction to the two manuals I have written on Mod/Con Equipment ( a third manual is just being finished up). It is the introduction and gives a fairly simple explanation of Mod/Con and expected savings compared to conventional equipment.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,450
    This is a pretty good brief overview


    A large portion of the savings comes from the modulating part of mod/con,as well as the usually standard outdoor reset that most mod/cons use. These are not reflected in the AFUE test
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Jason_13
    Jason_13 Member Posts: 299
    High efficiency???

    It depends. As I always say if you do high efficiency boilers you need to do high efficiency homework which a large percentage of installs failed to have done. If you don't do your homework do a cast iron boiler cause that's all the efficiency you will get.

    I will tell you I believe that 80% of everything installed today is at least 100% over sized. That will short cycle your mod/con and kill the efficiency. I was at a job site two weeks ago. There were 4 boilers one in each building. This was low income housing. The boilers had about 1076 hours of operation with a little over 40,000 cycles. That is an average run time of just over one and one half minutes. This is many jobs in a year like this. I get on many more problem installs that new installs.

    If you want it done right do the heat loss at two outside design temps.  One at your coldest design temp and a second at around 60f. This gives you the heat loss at both sides of the spectrum. Next measure the radiation and calculate the maximum and minimum water temperatures. If the load is between two boiler sizes most will choose the larger. Then turn your fan speed down to limit the input to the heat loss. Usually you will also be able to turn done the DHW fan speed to match the input required for the indirect. To fire the boiler higher than the tank can handle is a waste of fuel and will not heat any faster.

    Next proper piping and flow....again do the homework.

    If all steps are not taken then install a cast iron boiler still properly sized, two stage OD reset and the fuel bill will not be much different than the mod/con will cost you.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,450

    I basically agree with you, but what makes you think that a person who oversizes a mod/con won't oversize a CI boiler? At least  a 5 -1 turndown mod/con can run  between 40-100% of the actual heat loss if  oversized by a factor of 2. The oversized CI is oversized, period!
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Jason_13
    Jason_13 Member Posts: 299

    I agree that is what the last line states. If properly sized, OD reset and properly piped cast iron boiler.

    We can't argue the point of that everything should be properly sized. The problem is so few are properly sized today as in the past.
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