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Will vacuum increase efficiency?

Dave in QCA
Dave in QCA Member Posts: 1,786
Most of the information that I am able to find indicates that steam systems are inherently less efficient that hot water systems because the boiler has to get hotter to make steam.  It stands to reason that since subatmospheric systems will produce steam at lower temperatures, (as low as 160 F according to information I have read) they would be more efficient to operate.  I have read threads that indicate that the steam will run out faster with a vacuum, but not much on increasing the overall efficiency of the system be reducing the boiling temp at the boiler.

Is my assumption a vacuum system will operate at a higher efficiency correct?  Are there vacuum / condensate return units available for a 2 pipe system with a total EDR of 2000 sq ft?  Is there any other way to adapt a 2 pipe system, that appears to have originally been a vapor/vacuum system, and make it run in a vacuum and thus at lower temperatures?
Dave in Quad Cities, America
Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.


  • Not really.....

    Those that state that steam is not as efficient as hot water are only looking at flame to water efficiency, not system efficiency.  When factoring in the fact that hot water systems use many times more electricity for pumping, that is roughly 15 to 30% overall efficient, steam starts looking a whole lot better, and may surpass the efficiency of hot water systems, especially as Modulating and condensing steam boilers become available . Vacuum is supposed to help greatly, according to documentation, and if the system was designed for vacuum, essentially it always needs to run vacuum to operate properly.  There is vacuum equipment available for virtually any size system.

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