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condensing boilers for high-temp application

NEVER apply a modcon to a "high temp" system. They are missing out on a minimum 30% reduction in energy consumption due to their purist (Snob Cons?) attitudes.

I have not sold a conventional boiler in over 8 years, and I do not regret it. Even high temp systems only need extremely hot water for very short periods of time.

I say go for it. Just make certain you follow the manufacturers recomended piping practices, and all will be well.



  • Jim_88
    Jim_88 Member Posts: 13

    What am I missing- Condensing boilers work most effectively if the return water temp is as low as possible (like the temp needed for infloor or underfloor applications). As long as the return water temp is low enough for condensation to occur in the flue gases. What if you want to use a condensing boiler in (what is usually termed) a high temp application- that is, using baseboard radiators. What is done in this situation??? Lower water supply temp and spend more for length of baseboard? Something fancy with primary/secondary loop????So, what am I missing here???

    Anyone know where I can go to design this? It will be (I hope) a multizone system, with controls for OA temp reset.
    By the way: I've chosen a Weil Mclain with multiple circulators using some kind of pex piping to the individual baseboard radiators. Or, using one of those homerun piping circuit gadgets.

    Any ideas????
  • Modulation.

    Most all condensing boilers have modulating burners. So even at high temps you will still modulate the burner to match the load.

    Running the system at a lower temperature and installing more base board is a way to ensure you condense more often. Either way you will still save with a mod/con.

    I am with Mark. I have not installed a conventional boiler in over 8years as well.
  • bobbyg_16
    bobbyg_16 Member Posts: 11

    Thanks Mark E. for making the atteched information available to "the wall" this past June.

  • Jed_2
    Jed_2 Member Posts: 781
    So, what about

    modulating, non-condensing, wall mounted boilers? If the system is all hi-temp, and it is a replacement boiler; why pay the premium for excess, un-achievable effiency, when usage will sweeten the HO's bottom line with either?

  • Mike E_2
    Mike E_2 Member Posts: 81

    Because it is achievable since you only need the high water temperature during the coldest days of the year. The rest of the winter when temperatures are milder you can reduce the water temperature and get higher efficiency.

  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 716
    Here's my deal...

    I've got a Knight 80 feeding 3 zones of baseboard designed for 180 at -20. We've added some insulation years ago and are at about an R44 or so. Previously the insulation was about 6 inches deep. So the baseboards are a little over sized for our current situation. For most of the season, there was plenty of condensing and the boiler was running at less than 50% output. I think that condensing is great, but it is talked about a lot more than modulating. The modulating is where I believe the most savings are. But, the difference in price for a boiler that only modulates verses one that both condenses and modulates is, as far as I know, not that great. For anyone looking at replacing a boiler these days, why even propose anything less than the most efficient system out there. The price difference is too low to sweat about. The payback is reasonable and my savings in the first season were about 30% compared to a cast iron slightly oversized boiler that I had added reset to some five or six years ago.

    Just my two cents worth.

  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,691
    You are very correct Larry..........

    But we find ourselves the lone-wolf, educating clients when the "others" - often long-established companies - poo-poo new technology. The people who come to The Wall are very unique and rare. Many - average Joe clients consider price FIRST and only. With the spike in fuel costs lately....it HAS gotten better but not tremendously so. Mad Dog

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 716

    I know what you are talking about. And while there will always most likely be applications for cast iron boilers, the trend in natural gas prices will hopefully make it a little easier to promote the most efficient products out there. Remember, people poo-pood fuel injection in cars too as too complicated and prone to failure. Tell me where you can get a car with a carburetor now!

  • steveex
    steveex Member Posts: 95

    When you say high temp,you speak of 20 to 30 days depending your location, what about the other 110 days, think about it.
  • steveex
    steveex Member Posts: 95

    Also mod. a must, years ago i seviced a 9,000 SF house in brooklyn ny. System had 2 cg 8 boilers feeding rads and #80 WM indirect. So one boiler was down and needed a t couple, PS forgot to go back and install it. 2 years later did a start up and remembered one boiler was out, home owner never complained about heat or hot water. Learn from others mistakes.
  • Jim_88
    Jim_88 Member Posts: 13
    mod/con boiler used in \"high temp\" applications

    thank you all for your input. I've contacted Weil-McLain (since I'm considering their Ultra boiler) for a simple explanation- how do I size baseboard if I use your Ultra: I assume it's based on worse-case, i.e.: 180F water temp w/20F delta T. Then, I assume their control system automatically modulates downward and reduces water temp to insure condensation (actually, that's probably where it starts- then modulates upward to worse-case scenario).Actually, since return water temp is the deciding factor (for condensation)perhaps the modulation is dependant on return water temp?- I really wonder how these control systems work.I hope they contact me.
  • Tony_23
    Tony_23 Member Posts: 1,033
    I would suggest

    I would suggest hiring an installer who knows the equipment and understands it. Also, it is preferrable to hire one who knows how to design a system to operate properly within the parameters of your home and the equipment selected.

    A Weil-Mclain Ultra is generally not a DIY project, nor one should be undertaken by an inexperienced installer alone.
This discussion has been closed.