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Are there any condensing residential steam boilers out there?

iLikeDirt | Posted in Mechanicals on

Or is there just mid-efficiency stuff? This is for steam heat, not hydronic.

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  1. GBA Editor
    Martin Holladay | | #1

    There is a thread on this topic at the site. I'll quote relevant sections.

    Q. "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?"

    Answer #1. "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."

    Answer #2. "Guy is correct. The two concepts are mutually exclusive. Steam is hotter than the dewpoint of the flue gasses by about 80 degrees."

    There's more to read there if you are interested in the topic.

  2. Dana1 | | #2

    212F steam is far too "wet" for use in a heating system, resulting in condensing a good fraction of the steam in the distribution plumbing. Residential steam heating systems are typically designed for 215-220F steam. The temperature of the condensed steam returning to the boiler is under 212F (quite a bit lower, in most cases), having given up heat to the return water plumbing (what, pipe insulation isn't PERFECT? :-) ), but it is still WAY above the ~125F needed for natural gas exhaust to condense at the heat exchanger plates inside the boiler.

    Commercial condensing steam boiler economizers exist, but they operate a very different duty cycle & purpose than residential heating systems, and are not readily adaptable to residential heating.

  3. iLikeDirt | | #3

    Thanks guys.

  4. motoguy128 | | #4

    It's possible if you had
    1) a 2nd low temp load like radiant floor heat or low temp baseboard
    2) sized proportionally to the steam radiator capacity for that spaces heat loss, and is equal to >7% of the total load. Indirect DHW tank can also feed this.
    3) You now need induced draft and downdraft burners, like a Weil McClain GV90+.
    4) Still have to use SS flue because it might not always condense.

    Cost and comnplexity

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