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Condensing Boiler for Steam Heat

ttekushan_3 Member Posts: 958
One percent efficiency gain for every 40 degreeF increase in combustion air temp. Net stack temp decreases with increased efficiency but total stack temp increases. Which is fine unless you want to follow that with a condensing economizer. I'm assuming that in plotting curves for each function, an optimal balance point will appear to allow condensing while increasing combustion air temp.

Ya know, Economizers have been around for a long time in the industrial steam sector. You can even get condensing economizers! But since they are externally applied to the system in a loop AROUND the boiler, its not part of the boiler efficiency rating per se. So steam is now inefficient?!! Gawd, the way components are rated outside their application and system really gets my boxers in a bunch.

But the trick is, you just have to have a place to put the recovered heat once you extract it. And oversizing boilers in this kind of set up really makes this difficult in a heating application.

My thoughts:

Air to air heat exchanger to increase combustion supply air temp and an economizer to extract more energy. Perhaps a condensate recovery vessel even for gravity return systems would be a good place to put the heat, and/or a diverter to a DWH heating zone. Or a heating loop for a garage. Or that hot tub. Or ice melt. Yea. Ice melt for free from formerly wasted energy! Ahhhh, the possibilities.



  • Peter von Bergen
    Condensing Boiler for Steam Heat

    I like the efficiency possible with new high efficiency condensing boilers, used for furnaces or hydronic systems.

    Can they be used for steam heat as well and does anyone make one with an oil burner?

    (PS I am posting this same query on the HighEfficiency forum)
  • Guy_6
    Guy_6 Member Posts: 450

    As far as I know, there is not anything available for steam that fits the bill. Condensing boilers are limited in their ability to condense as output temperatures rise. Steam, at 212(or so), is the hotest that atomospheric pressure water can get, therefore condensing within the boiler would be NEARLY impossible. I say NEARLY , as I know that there are some brilliant people that lurk here who can probably devise a way that it might happen. Happen on purpose, that is. I have had Mod/Cons make steam, but it wasn't pretty...
  • Brad White_145
    Brad White_145 Member Posts: 17
    Guy is correct

    The two concepts are mutually exclusive. Steam is hotter than the dewpoint of the flue gasses by about 80 degrees.

    Not to say that there is not condensing going on during a cold start or that you cannot make cold steam by using a vacuum system... but for all that trouble you could have a hot water system on wheels.
  • Steamhead (in transit)
    90%+ efficiency on steam

    is doable, but with recirculation rather then condensing technology. Two companies I know of that market this in their larger commercial boiler lines are Gasmaster (Canada) and Hoval (U.K.).

    American boiler makers are conspicuous by their absence from this efficiency level. The only one to step up to the plate and offer a higher-efficiency steamer is Burnham, but the MegaSteam only goes to 88% or so and they don't offer it with a gas gun yet. C'mon guys, your silence is deafening.

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  • Uni R_2
    Uni R_2 Member Posts: 589
    Theroetically speaking...

    Theoretically speaking at 25 inches of vacuum water would boil at 133F.

    Maybe have a condensing boiler feed some special heat exchanger that passes the boiler water at atmospheric pressure on one side of this HX/boiler and makes steam at that temperature in a vacuum on the other side.

    It would be pretty tough to do - that's a lot of vacuum!
  • brucewo1b
    brucewo1b Member Posts: 638
    And I'm guessing

    big radiators for those cooler temps.
  • Uni R_2
    Uni R_2 Member Posts: 589

    With a modern well insulated tight home could you see them as actually looking proportional?
  • Boilerpro_5
    Boilerpro_5 Member Posts: 407
    Actually not exclusive, I believe

    Steam or water does not need to be the condensing agent. My Dunkirk Quantum uses the cold intake air as a condensing meduim to cool the exhaust to much lower temperature. The exhaust on the boilers runs about 20F BELOW the water temperature and the boiler continues to condense up to 180F water temperatures, or so. No reason this can't be done with a steamer.


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  • Brad White_146
    Brad White_146 Member Posts: 25
    That would be interesting to see.

    I wonder what the efficiency gain would be by preheating your combustion air. It makes sense as nothing else in the chain of energy is colder than the flue gasses and any cold make-up water.

    But as a general statement, commercially available steam boilers are not condensing- on the combustion side at least. :)
  • Christian Egli_2
    Christian Egli_2 Member Posts: 812
    Steam boilers not breaking a sweat

    Irregardless of where boilers get the cold they need to condense flue gas, whether it be from the tepid return water or the frozen cold outdoor air, system wide efficiency modifiers for boiler come in two form.

    One - squeeze out more than the usual (80+)% from the fire by cashing in on the condensation heat of the piles of water vapor you get when burning natural gas (you get less with oil). This method bumps you up a few points in efficiency, but... most often (though not necessarily) at the cost of operating your system with a cooler fluid.

    Two - play with the system fluid temperature. A low temperature fluid only carries low grade heat which is very hard to use efficiently. Bump up the operating system temperature, and you get yourself increased thermal efficiency, at the cost of the condensation heat recuperation.

    Playing with number one messes up number two, and vice versa, in about the same proportions. An, albeit hotter, steam scheme operates system wide with the same efficiency a low temperatured, and thusly condensing, hydronic hook up.

    Here's what I think is the biggest achievement

    Most of the benefit and savings coming with modulating and condensing boilers have to do with the near perfect control you can reach with these machines. Brains. By avoiding all or most of the home overheating you would otherwise experience with crude thermostat control, you save yourself a lot of expensive heat. And that's very good.

    Steam systems are not unresponsive, they benefit greatly from superior control strategies, but not as much as a hot water system which is harder to control with unsophisticated methods (plainly because of inertia and delay problems and weak heat carrying ability)

    It only follows there is more push for more evolved hot water control and more evolved hot water boilers than there is equivalent cuddling for steam - the reward is bigger. That said, all this is still no reason not to look into anything that makes us enjoy steam even more.

  • Weezbo
    Weezbo Member Posts: 6,232
    i have seen some interesting configurations..

    on English web sites...i have an idea *~/:) i will see if i can find it again :)

    there are some really cool looking heat exchangers and the preheated gas comming in with the secondary heat exchanger being heated by return water through what looked like pipes through the condensate pan on the back of it...

    whatever :) thing is all the new boilers are to be 90% minimum...so that really does allow for some ingenuity...

    they must be engineering the Frith out of them.

    speaking of oil condensing the Green star Heat Slave might be a boiler Product of or product sold by Buderus that condenses and burns oil....buh i am pretty sure it is a hydronic boiler...
  • Boilerpro_5
    Boilerpro_5 Member Posts: 407
    It would be nice if Burnham offered....

    a gas gun and a add on combustion air condensor for that unit. I bet it could be a great combination.

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  • Ken_40
    Ken_40 Member Posts: 1,320
    Interesting thoughts...

    If we were to apply a vacuum to the system, as we did in vapor/vacuum systems 50 years ago...

    Water would boil at under 212F, making the steam chest, if around 140F, would induce high rates of water-laden combustion gasses and the resulting condensation, and best of all:

    The latent heat of steam condensing to water at any temp is where the true "heat" comes from! ~1,000BTU's/lb of water as it changes state!

    Think about it! Boiler water temp at ~140F, suck a system vacuum, voila! Steam AND condensing. Hell, they did it without a vacuum pump 75-years ago! They simply designed a system that created its own vacuum!
  • MiaLisa Morris
    MiaLisa Morris Member Posts: 5


    I rent, and since I been here, a new boiler was installed for my apartment (I pay for my own heat, gas, & hot water). Anyway, I recently ran into a problem with the thermostat and now I have to go to the basement to turn/off the boiler for my heating needs (until the repairman comes). When I turn on the boiler, the radiators are constantly leaking. What shall I do?
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