Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

vari vac steam controls

viv Member Posts: 9
hello,I just on to a job that has a dunham bush vari vac on the steam suppy,could ony one tell me what is this control suppose to do and how it works? thanks


  • VariVac

    You must be referring to the valve. The valve had a modulating motor to open and close the valve in conjunction with a fairly sophisticated vacuum control system. Almost all of these jobs heated domestic water off the boiler. Hence the need for the valve.

    Most of them have long since ceased to operate and the systems have been converted, in a manner, to straight steam systems with condensate return pumps. Never works right.

    The wise person will install a vacuum/feed water combo unit. Repair or replace all traps, and install a good heat control(s). We have had considerable success in zoning the systems w/ Heat Timers and MH V5011's. Might even try a Tekmar one of these days.
  • hot_rod
    hot_rod Member Posts: 21,844
    More than that, it is outdoor reset of steam temperature

    The Vari-Vac® Differential Steam Heating Control System precisely balances the heat input and the heat loss of a building by matching both the temperature and quantity of steam supplied to the measured requirements of the building. This is accomplished by varying the steam pressure in the steam supply main between 2 psig and 25 inHg while a differential vacuum pump maintains a constant pressure differential between the supply main and the return main to assure efficient return of condensate to the boiler. This pressure modulation results in high temperatures at the terminal unit (up to 218° F) during the coldest weather and low temperatures (down to 133° F) on mild days. The Vari-Vac® System thus provides the maximum in heating comfort and temperature control with unsurpassed fuel economy.

    These components comprise the Vari-Vac® System:


    They still use these systems in NYC

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • pfitter_10
    pfitter_10 Member Posts: 3

    Is absolutly correct! These are the Caddilac of steam heating. I have had the pleasure to work at restoring several of these systems over the years. When you put them back to their original design they are highly effecent and it will cost much less then and provide more comfort then abandoning or replacing it. If I'd had any more fun on these things, I'd a had to pay my boss! Contact your local Dunham / Bush Rep and tell him you want the big black binder full of vari vac info. Or Try http://www.statesupply.com/.

    You found a gem.... now polish it!

This discussion has been closed.