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Help restoring Hoffman System

OatKingOatKing Posts: 8Member
Hello all!
We moved into a 90 year old house in 2016 in Eastern Iowa. Just now getting around to understanding the steam system and my goal is to restore as much as possible throughout the house. Thank you all for the information posted here and on YouTube. Learning about this community was incredibly helpful to undertake this home restoration. My system has issues and I'm asking for advice on what needs to be done and improvements possible. I own and read LAOSH, "We Have Steam Heat" and spend many hours on "The Wall" reading and thinking. Thank you all again!

#1 Cycles on low water - condensate returns about 1-2 mins after shut down.
#2 Occasional mild water hammer - random occurrence.
#3 Hearing a strange sound, similar - but not the same as - air bubbles entering the office water cooler coming from the pipes
#4 Strange piping arrangement on wet returns [see top down photo]
#5 Wet return drains only a trickle from bib, Boiler drain doesn't drain any water.

More about my system:
2 pipe Hoffman vapor heat, with differential loop
Venting: Main: Hoffman #15 and 2x #18 crossover traps, 1 air vent on rad. on 2F BR (I understand this is covering up some other issue).
mostly #18 traps. various working condition
mostly #7 valves. various working condition
16 total radiators and in-wall convectors. (no EDR calculation yet, waiting on E.D.R. book),
Boiler: WM EG-65 approx. 20+ years old
Insulation: Asbestos w/ a little fiberglass
P-troll: in: .5 / out: 1.5psi
LWCO: Safgard 400
Auto feed: VXT-24 on 2min delay/2 gallon feed

Please let me know if you have any follow up questions, I tried to start out with the basics first.


  • ethicalpaulethicalpaul Posts: 1,335Member
    edited January 7
    I think your near boiler piping is horrible, but I can't tell for sure, because, frankly, your photos are kind of bad.

    Can you take some where the boiler itself is in the center of the photo and far enough away that the floor and ceiling below and above the boiler appear? And from like 3 angles?

    Like image#1 is close, but I can't see the whole boiler and the immediate pipes around it.
    1 pipe Utica 112 in Cedar Grove, NJ, 1913 coal > oil > NG
  • dopey27177dopey27177 Posts: 115Member
    Here is what the system should look like.

    It appears that some one worked on the system worked on the piping and may have removed something.

    Need better pictures.

    The devices shown in the drawing may look different from the Hoffman equipment but all the parts are basically the same.

    What may be problematic is the lack of check valves at the bottom of the return system or defective or missing steam traps.

    I believe you may have a modified vapor steam system. They usually operate at 1 lb steam pressure or less.

    Enclosed is a drawing from my book.
  • Zipper13Zipper13 Posts: 120Member
    I'm a novice myself. But like you, I had the same problem draining my boiler at first. I was shocked to find that my original 100 year old Hoffmanvent still holds a vacuum. Early on I found the easiest way to break the vacuum and allow the water to drain was to remove the vent from the differential loop before opening the drain. I have since added a valve and skim port which I can open to break the vacuum before I drain.

    I'm sure you will have a vaporstat recommended. I thought about upgrading from my pressuretrol to a vaporstat but found that my system never exceeded 3 oz of pressure anyway so decided I don't need to cycle on pressure.

    I have found that my Burnham boiler is very sensitive to the fill level. My boiler guy fills it 2/3 to top of the sight glass after cleaning each season, but the boiler bangs there, so I drain it an inch lower and it's silent.

    Just my ameture two cents.

    You're going to get some great feedback here. Several helpful Hoffman fans are on this board!

    New owner of a 1920s home with steam heat north of Boston.
    Just trying to learn what I can do myself and what I just shouldn't touch
  • Jamie HallJamie Hall Posts: 11,857Member
    As @ethicalpaul says... hard to see what's what.

    To add to the photos he suggested, can you come up with one (or several? which clearly show the piping from the header to the Hoffman Differential Loop, and the way the dry returns are linked to the top of the Loop (with the vent(s)), and the way the wet return from the Loop connects to the main wet return?

    A few other comments.

    First, the Hoffman Equipped system such as yours must have one, and only one, venting location, and that venting location must be at the end of the dry return(s) after they have hooked together and immediately before they drop into the Hoffman Differential Loop. There could be multiple vents there on an antler arrangement, but that's it. You may need more main venting at that location, but the existing Hoffman #15, assuming it is working, may be quite adequate. You will need a low pressure gauge to verify that.

    Vents anywhere else on the system will defeat the purpose of the Hoffman Differential Loop and cause odd results, depending on where they got stuck on. Get rid of them. The vent on the radiator may be covering up for a failed closed trap or for a return line which is pitched incorrectly and holding water. Or just a mistake...

    For better or worse, a Hoffman Equipped system must be controlled with a vapourstat (like most other vapour systems). The cutout must be set at no more than 7 ounces, with a cutout usually around 3 to 4 ounces. Any pressure over that will trip the Differential Loop and result in variations on poor to no heating. I suggest you keep the pressuretrol, but mount a vapourstat and low pressure gauge somewhere handy.

    Your comment on draining from the boiler drain and the wet return -- plus the slow condensate return -- suggests very strongly that it is past time the wet returns were flushed out, as well as the boiler drain.

    Weil-McClains are moderately forgiving on near boiler piping, but what little I can make out is not encouraging. I'm particularly concerned that the line from the header to the Differential Loop may not be done properly.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • OatKingOatKing Posts: 8Member
    Thanks and sorry for the small photos! They were 5MP on my phone so I reduced the size. Late tonight, when I return home, I'll take some better, larger and labelled photos. There's a hydronic loop and DHW heater that are completely separate, but physically close to the boiler, adding to the obstructions. I can understand why it's hard for others to see what's going on.

  • Jamie HallJamie Hall Posts: 11,857Member
    That should be "cutout at no more than 7 ounces and cutin usually at 3 to 4 ounces..." in my post above.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • SteamheadSteamhead Posts: 13,501Member
    @OatKing , where in Iowa?
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • OatKingOatKing Posts: 8Member
    @Steamhead Cedar Rapids, City of Five Seasons.
  • EBEBRATT-EdEBEBRATT-Ed Posts: 6,306Member

    Near boiler piping the "header" is too close to the water line. Should be 24" minimum above the water line. Lots of issues but if you read the LAOSH you already know that.

    You going to have to start from scratch and pick your way through it......You can save it and you should.

    I would start with edr calculation to see if you should keep the existing boiler.

    Fix near boiler piping

    go through all the traps and venting.

    Thatt's enough to get started
  • OatKingOatKing Posts: 8Member
    @ethicalpaul - kindly see images 6, 7, 8

    @dopey27177 - thanks for the docs. There are a few terminated connections, (one original, one later added). The diagram looked complex, so maybe previous modifications removed multiple items.

    @Zipper13 - thanks for the suggestion about breaking the vacuum to drain. Will try tomorrow.

    @Jamie Hall - kindly see images 9, 10 for the Hoffman connections. There supply to the differential loop doesn't directly connect to the header, it comes off the main steam line, near the ceiling.
    The overflow connection to the wet return is the pipe running right below the draft good.
    Because the Hartford loop is so tall (36" tall and 20" above waterline, I wonder if the installers placed the rad vent because the current configuration doesn't allow air on that leg to reach main vent.
    The Hoffman #15 appears to still work. I let you know the pressure when I replace the pressure gauge.
    Will remove and plug the rad. vent, pick up a vaporstat, install a low pressure gauge and let you know.
    @EBEBRATT-Ed - Correct, the header is about 6" too low. I will calculate the EDR for the entire system.then decide what to do with the boiler.
  • ethicalpaulethicalpaul Posts: 1,335Member
    Thanks, those are nice photos! As others said, I don’t like the low header. I also don’t like how the tee off the header comes off horizontally.

    Also that’s a big boiler for just one steam supply pipe.

    It’s my opinion that for these reasons, this near boiler piping will carry a lot of water into your main.

    There is good height up to the main, but the water will get carried up there like an old coffee percolator. Ilike @EBEBRATT-Ed ‘s advice
    1 pipe Utica 112 in Cedar Grove, NJ, 1913 coal > oil > NG
  • Jamie HallJamie Hall Posts: 11,857Member
    So long as all the dry returns tie together above the top of the Hoffman Differential Loop, you don't need any other venting on the system -- and don't want it. The connection of the steam line to the loop from the main isn't ideal, but it is one way of doing it and quite valid.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • dopey27177dopey27177 Posts: 115Member
    Look at my drawing again.

    it appears that there is no air separator in the system.
    Find the 1/2" radiator trap on the system. It should be on your dry return piping (some times there are 2 or three of them) that depends on the piping configuration.

    Also look for the the air check, that can be clogged or stuck .

    These parts can be disassembled and cleaned.

    Check the heights where shown. These are minimum dimensions. If grater its OK. These dimensions are to assure that the dry returns do not get water in them where they connect to the wet return.

    Getting back to the steam traps on the system. Barnes and Jones manufactures internals for all your steam traps. Purchasing new traps and installing them can get real expensive.

    Getting back to to steam pressure settings. Maximum steam pressure should not exceed 12 oz. with a differential of 4 oz.

    You may need to reset the vaporstat or replace it.

    EDR calculations are not needed. Vapor systems have larger radiators than steam systems operating at at pressure. Example,
    1 pound pressure steam is 215 degrees. 3/4 pound pressure is about 213 degrees, but your system can operate at in a vacuum up to 15" That is steam at a temperature of 182 degrees.

    The heating system when tight will normally operate in a vacuum.

    Hoffman accounted for the lower steam temperature by installing larger radiators.

    The lower temperatures emanating from the radiators kept the air from drying out and as a result the heat was more comfortable. ( less dry nose conditions)

    Check the radiator valves to see if they are adjustable or have orifice plates in them)


  • Jamie HallJamie Hall Posts: 11,857Member
    I'm sorry, but I have to differ, @dopey27177 . The Hoffman Differential Loop -- any size -- is calibrated to trip at between 7 ounces per square inch and 8 ounces. No more. The cutin should be around 3 ounces. Any higher pressure differential will trip the loop, and that is -- at best -- undesirable.

    If that Hoffman #15 is operating properly and the radiator and crossover traps are operating properly and the pressure never rises above 8 ounces, it will never see steam. It should, however, close on a vacuum.

    I'm not sure to what you are referring by an "air separator", nor an "air check". Possibly you are referring to what I term a crossover trap? In most cases those are standard Hoffman radiator traps and yes, if they are malfunctioning, they can be disassembled and the internals replaced.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • dopey27177dopey27177 Posts: 115Member
    Just noticed you have an air valve on one radiator. Remove it. It is affecting the vacuum in the system.

    you have a blown steam trap some where in the piping system.

    Plug off the vent valve tapping. This will allow the system to go into a deeper vacuum.

    See if the problem on the radiator is (does not get hot enough)

  • OatKingOatKing Posts: 8Member
    @dopey27177 : Thanks for the advice. I agree that there is one (likely several) traps that need to be replaced. I will wait until spring to tackle the traps when I can tear into the system, but I will put the air vent from the rad. to check see if that rad. alone is cold or the entire loop. I will get a vaporstat and low press. gauge once I loosen the old fittings. Just about every valve or fitting is either plugged or seized.

    @Jamie Hall : can you explain your comment a bit differently about "as all the dry returns tie together above the top of the Hoffman Differential Loop...", I am trying to understand the path air takes getting back to the main vent.

    @EBEBRATT-Ed: I received E.D.R. and began compiling my radiators - Thankfully they are listed. Since the 8 convectors are in the wall, covered by plaster I'm trying to estimate based on size and enclosure height. Since EDR assumes 215F and 1PSI, how would running vapor system on less pressure and possible lower temps effect the calculation?

    For the group, since the NBP is poor and the boiler is likely 20+ years old, should I look into replacing the boiler with the piping?
  • EBEBRATT-EdEBEBRATT-Ed Posts: 6,306Member

    The change in btu's from 1psi to vapor will not change the output enough to make a difference.

    Once you get your radiation total compare it to the boiler nameplate.

    I would get the system running as best you can with traps, venting check piping pitch etc and see how it goes.

    Then make a decision about the boiler later based on the edr you need and the boiler needing to be repiped.

    I would not repipe until the boiler is changed
  • Jamie HallJamie Hall Posts: 11,857Member
    On dry returns (oh no, here we go again) for vapour steam systems. The dry returns for a vapour steam system -- indeed, any two pipe steam system -- carry the air and condensate from the steam mains and from the radiators. The air and condensate from the radiators gets there through the radiator outlets -- which in many vapour systems, such as the Hoffman Equipped systems, have steam traps which prevent the passage of steam, but allow air and condensate to pass (some other vapour systems use a combination of orifices or interesting static widgets to ensure that only air or condensate reach the dry returns; the effect is the same). Almost all such systems originally had crossover traps from the ends of the steam mains to the dry returns. These are essentially identical to radiator traps (in fact, the air capacity of a radiator trap is high enough that most systems used the same traps as the radiators). They are placed above the steam mains, and so allow only air to pass. Condensate from the steam mains in parallel flow systems (the vast majority) was handled either by a drip to a wet return or, more rarely, by a water loop seal arrangement which established a water seal between the steam main and the dry return, allowing condensate to pass but neither water nor air.

    So. Summary. Air and condensate from the radiators passes through the radiator traps into the dry return. Air from the steam main passes through the crossover traps into the dry return, and sometimes condensate passes through a water seal into the dry return (rather rare, actually).

    Note that steam is never present in the dry returns (under normal operation, but see below).

    Further, the air pressure in the dry returns is very close to atmospheric (again under normal operation -- again, see below).

    Now. The air has to get out of the dry returns somewhere. Since neither radiator traps nor operators are goof proof, almost all vapour systems employ air vents to exhaust the air (a few earlier systems were simply open to the atmosphere). The simplest place for the air vents was and is at the boiler. Thus all the dry returns can tie together at the boiler and share a single vent (in more modern systems, it's usually two or more vents -- but they are all in the same place). Any condensate in the dry returns at that location is allowed to drain down to the boiler wet return to join the condensate from various system drips.

    It should be noted that many vapour systems used vapour vacuum vents, such as the Hoffman #76 or #15, rather than our now standard vents. These vents allowed air to pass out, but sealed against a vacuum, thus placing the entire system under vacuum and allowing it to operate at lower temperatures when the fire (in the case of coal) was damped, or when the burner (in the case of oil or gas) was turned off and the system was cooling. There are some advantages to this; whether they are worth the additional cost of the vacuum vents is debatable.

    At this point, it is well to note that there is a complication in many vapour systems: devices intended to keep the differential pressure between the steam mains and the dry returns to some low level. Keeping this differential low serves to prevent -- in most cases -- the water from being forced out of the boiler by high steam pressures (high is relatively speaking here) and from blowing the various water seals. These devices -- of which the Hoffman Differential Loop is perhaps the most common -- function by introducing steam from the header into the dry returns and, at the same time, closing the vents so that pressure will increase in the dry return if the differential pressure is too great (typically about 8 ounces per square inch). This is the only time in these systems when the vents will close, unlike ordinary two pipe and all one pipe systems where the main vents on the steam mains will close frequently and on every cycle. But, in order for this to work, the vents must be at the same location as the device in question, or very close, so that the steam can reach them immediately and the pressure can build as needed in the dry returns. Thus all the dry returns in these systems must be joined together at one location, and the only vents in these systems must be located at that location which is also where the device is located and which is, of necessity, at the boiler.

    A bit long-winded, but I hope that helps.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • dopey27177dopey27177 Posts: 115Member
    Jamiehall made a perfect description of the operation of vapor vacuum systems.

    Without a drawing of the system words do not help much. Jamie hall works on these systems which come in various configurations. See the attachment for a picture of a one of the expensive installations of its time. follow his words to the picture
    and you get a better understanding of your system.

    As far as the heating elements go they were sized to provide the
    BTUs needed at steam temperatures as low as 180 degrees f.

    Today if your system was working correctly you might find the house to hot because storm windows, new weather stripping and a tighter house than originally built.

    Additionally if the steam mains are not insulated the steam will condense into water and you will lose the steam volume needed to fill the piping system. You need cubic feet of steam to fill the piping and radiators.

  • OatKingOatKing Posts: 8Member
    @EBEBRATT-Ed : the EDR of my system is 738.2 sq ft - without adding the pickup factor. I realize my boiler(WM EG 65) can only supply 654sq ft. Adding the PU factor of 33%, would take EDR up to 981. I will post my specific rads and conv. to show my work a little later, but an undersized boiler was not a conclusion I suspected.

    @Jamie Hall : thank you so much for the indepth explanation about venting. It finally sunk once I realized that once air passed the crossover trap, it move against the condensate flow in the dry returns to the main vent.

    @dopey27177 : I removed the air vent on the radiator and installed a plug. The system still cycles on low water but the condensate returns faster and noticably more of it.

    I haven't checked the line pitch yet. I'll wait until spring when the asbestos insulation removed. Right now I am still processing all the information gathered. I am so thankful for this community as I go along with this process. Just yesterday, I found in the library, information on Trane Concealed Heaters and able to get exact calculations on my system EDR. Thanks again, everyone!
  • OatKingOatKing Posts: 8Member
    Attached is my EDR calculation. I made an error earlier, so the actual EDR is 702.55 - about 35 sq ft less. There is also a discrepancy in my boiler's capacity, the manufacturer's document states the EG-65 supplies 654 sq ft, but the data plate and IBR certification states it only supplies 633 sq ft of steam.
  • Jamie HallJamie Hall Posts: 11,857Member
    The boiler is big enough. You don't add anything for the "pickup" when calculating your EDR, and the boiler manufacturer does -- 33%. So there's enough capacity. Only thing -- insulate your steam mains if you haven't.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • OatKingOatKing Posts: 8Member
    Thanks @Jamie Hall. Currently, the steam mains are insulation with asbestos. There are a few spots where the radiator take offs approach the foundation and floor joists that are uninsulated but I plan to correct that when I re-insulate in the spring.
  • Jamie HallJamie Hall Posts: 11,857Member
    You can also encapsulate the asbestos in place, if you don't disturb it it's not really a hazard. On the other hand, if you go to sell the place someday, the buyer likely won't be happy...
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
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