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A Hartford Loop Q & A

HeatingHelp Administrator Posts: 586
edited April 2022 in THE MAIN WALL
A Hartford Loop Q & A

The Hartford Loop is an arrangement of piping between a steam boiler’s header and its gravity-return piping.

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  • dgn
    dgn Member Posts: 29
    What about a Gifford Loop where the return connects to the equalizer above the water line? Described here:
    I have this setup and never a peep of hammer. Water line in glass bobs about an inch or so when boiler is firing. Aside from this article on HH, curious why I rarely read about it.
    Danny Scully
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,573
    Good question! Was your Gifford loop installed by design, or by accident? How high is it in relation to the waterline?—NBC
  • dgn
    dgn Member Posts: 29
    I can't say for sure, but I'd guess it was installed by accident. Why? The waterline in the glass, after condensate returns after shutoff, is just about even with the middle of the close nipple going into the equalizer. So the waterline is probably a bit below the return when firing. Given the lack of hammer and amount of bounce seen in the glass, I guess it's working out fine for my situation.

    Still, I'm curious why far more discussion about Hartford Loops than Gifford if the referenced article states the Gifford is a superior solution.
  • Dan_NJ
    Dan_NJ Member Posts: 220
    "A Gifford Loop is like a Hartford Loop, except that the bottom of the inside of the close nipple is located above the boiler waterline rather than below it. (The waterline is defined by the level at which an automatic feeder would start feeding water.)"

    So from the article they are not talking about the "normal water line" of the boiler, but rather the auto-feed water line? I don't have an auto feeder. How far below the boiler normal water line would an auto feeder normally be set up to start feeding? If that point is more than 2" below boiler normal water line and my Hartford loop connects at 2" below boiler normal water, isn't it already a Gifford loop?
  • dgn
    dgn Member Posts: 29
    Dan - As shown in the diagram at the top of this article, the loop connecting below the water line is a Hartford. I believe this is what you're describing your setup is. In a Gifford Loop, the return is above the waterline of the equalizer (and normal water line).
  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,289
    Yes, the drawing shows a Hartford Loop.
    Retired and loving it.
  • AMservices
    AMservices Member Posts: 605
    I use the Gifford loop on every steamer I install.
    No problems with banging. Only it's even more important that the connection be made with a st 90, close nipple and 90, or "y" fitting.
    Compared to boilers I see during service, water line is stays much more stable.
    Make perfect sense.
    If any pressure builds in the boiler, the force of that pressure will push down on the surface of the water. If there's a port lower then the water line, water will be pushed through it, lowering the water level.
    That can't happen if the return connects above the water line.

    The Hartford loop was a evaluation to steam heating that saved countless lives.
    The Gifford loop does the same thing and adds better performance.

    Try teaching that to someone who's been installing steam systems for more then ten years, is like teaching a 10 year old dog to jump through a ring of fire.

  • GBart
    GBart Member Posts: 746
    I used to tell my classes that the Hartford Loop was where 91 and 84 intersect........no wait that's a disaster.
  • dgn
    dgn Member Posts: 29
    @GBart - Ha! Been there, drove that many, many times.
  • GBart
    GBart Member Posts: 746
    yeah, we've spent billions on that making it better, now they want to build a tunnel, Ct had this extremely poor concept of directing it's highway's to the cities thinking it would bring increased commerce and spending, it doesn't it brings gridlock and accidents, another classic is Rt 9 in Middletown, a highway with several sharp turns and two stop lights..........brilliant.
  • francisleblanc
    francisleblanc Member Posts: 1
    Hi, on the hartford loop header do we need to get a slope back to the equalizer or we can put that pipe level

  • Jamie Hall
    Jamie Hall Member Posts: 21,106
    @GBart and friends -- when I was a highway engineer (yeah really...) we used to use I84 in Connecticut for instruction. Somewhere in its length it has at least one example of every single kind of bad practice in design that can be found anywhere on any Interstate. Very useful to have all the catastrophes in one stretch of highway.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • jhewings
    jhewings Member Posts: 139
    @francisleblanc Your use of the expression "hartford loop header" is a bit confusing. The connection at the hartford loop, of the loop riser to the equalizer, should be as short as possible. A close nipple or wye fitting is preferred. The steam header above the boiler should slope down slightly towards the equalizer to drain any water in the header.
    EBEBRATT-Ed Member Posts: 13,438

    Your probably old enough to remember when I84 east got off in downtown Hartford and didn't connect to RT 91 without driving through a few city blocks to get back on 91 north.

    Sat in traffic there more times than I care to remember to get back to Springfield. What a mess.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 5,631
    edited April 2022
    There seems to be some question on exactly what makes up a Hartford loop. I was in a technical school class in the 1970s where a very old instructor (Mr. Spence who is one of the Dead Men) drew a hand fired steam boiler on the blackboard. It looked very similar to the diagram on the left. He used this diagram to illustrate the need for Dimension A. The condensate must be higher at the end of the main by about 28" in order to make up for the friction loss of the steam pressure at the end of the main compared to the pressure at the pressure at the boiler. Dimension A. can be different based on the operating pressure of the system. A vapor system could have a very short Dimension A.

    Then after we all understood the concept of Dimension A, Mr. Spence drew some additional lines on the board, much like the diagram to the right. He then taught us the reason for the Hartford Loop. I remember there were two. The primary reason was to keep the boiler from dry firing if there was a leak in the return. The second was to have the equalizer keep the higher pressure from the boiler from forcing water out and up the return in the event that closing radiator valves and partially plugged piping would make for a pressure sufficient to force the water out the return from the boiler, just in case Dimension A was not sufficient keep the water in the boiler. The equalizer would be close to the boiler and therefore exert the same pressure on both the supply and return.

    So my belief is that all the pipes that are not included in the first diagram are what make up the Hartford Loop.
    A. The Header to the equalizer Horizontal pipe
    B. The vertical combination equalizer/header drip,
    C. The Tee fitting just below the water line but above the crown sheet of the boiler on the equalizer.
    D. The close nipple
    E. The system return riser that connects to the Tee fitting C
    F. The riser from the boiler return to the Tee fitting C
    (C. and D. can be a Wye fitting)
    So there are 6 (or 5 with a WYE fitting) components to make a Hartford loop.

    Therefore @francisleblanc's term Hartford Loop Header is referring to pipe A. in my diagram. That pipe may be level or better if pitched to the return drip pipe B. Never pitched towards the supply opening of the boiler. This is to allow the condensate or water that may be in the header, to flow in the same direction as the steam leaving the boiler and header.

    If I am incorrect in this explanation of the components of a Hartford Loop, I would certainly like to know what are the necessary minimum parts that make up the Hartford Loop

    I respect the combined knowledge of this group, and hope that one of these frequent flyers can confirm or at least teach me something new. @DanHolohan @Jamie Hall @hot_rod @JohnNY @STEVEusaPA @Steamhead @STEAM DOCTOR @ethicalpaul (Who has a really awesome steam boiler setup) @EBEBRATT-Ed and others

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    STEAM DOCTOR Member Posts: 1,652
    @EdTheHeaterMan. Just to add a bit. Technically, the Hartford Loop and the equalizer are two different things, with two different functions. In theory, you can have one without the other. Let's say you decided to drain the header out the window. You obviously would not have an equalizer. But you could still have the loop, which should stop the boiler from emptying out if the wet return were to spring a hole (the boiler might still get syphoned out, I will let @""Jamie Hall" explain that). You can also have an equalizer without having a Hartford Loop. You can bring the wet return directly into the bottom of the boiler, while having a T which connects the header to the wet return. The pressure would be equalized but there would be no boiler protection if the wet return springs a leak. As far as I understand, there isn't much functional reason not to have the equalizer connect to the wet return, on the house side of the Hartford loop (meaning to the right of the loop in Ed's diagram). 
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 5,631
    @STEAM DOCTOR The Hartford loop without the equalizer would just be a trap. And the equalizer without the trap would only solve the Dimension A. problem. I always thought the combination of the 6 pipes and fittings was what the Insurance Company designed. The combination of the equalizer and the trap = the Underwriters Loop.

    Was I taught wrong? When I get to the "otherside", I'm going to give Mr. Spence a piece of my mind.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Jamie Hall
    Jamie Hall Member Posts: 21,106
    The Hartford Loop piping without a vent on it or the equalizer (preferably the equalizer!) is, as @STEAM DOCTOR said, a siphon -- and would quite happily drain all the water out of the boiler, despite being higher, if there were a leak in the wet return. The equalizer really does three things -- all of them well. First, it makes sure that the pressure where the wet return gets to the boiler is the same as the pressure in the header (which may be very slightly less than boiler pressure). Second, as noted above, it prevents the Hartford Loop piping from acting as a siphon. And third, rather trivially, it acts as a good drip for the header.

    As to various dimensions out in the wilderness, there are two factors in play. Maybe three. First, there will be a pressure loss in the steam mains. At full song, this may be several ounces or even a pound or so, depending entirely on the steam velocity and the pipe size. Thus the pressure on any drip out in the wilderness with be less than the boiler pressure. Second, there may also be a pressure loss in the wet returns -- although that is usually minor. Third, if the steam mains are vented or crossed over at the ends -- as they should be -- the pressure in the steam main at the ends will be atmospheric, or very close to it. Therefore (here's that A dimension!) the water will stand in any drip at an elevation sufficiently higher than the boiler water level to make the water pressure at the Hartford Loop equal to the steam pressure in the equalizer and header. It has to do this, because the steam pressure on the drip is usually much less than that at the header.

    The whole thing was dreamed up by the Hartford Insurance people -- hence the name -- as they were tired of boilers running dry because or leaks in the wet returns. It got expensive. It doesn't however, completely solve the problem! It does prevent the boiler being drained by a leak when it is not firing. It does NOT prevent the boiler running dry because the wet return has a leak when the boiler IS firing, however. So when firemen began to go the way of buggy whips and the like, they mandated low water cutoffs...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 5,631
    edited April 2022
    @Jamie Hall I totally agree with everything you say here. I just wanted someone to say what is included and what is not included in a Hartford loop. I think the highlighted section of the statement confirms my original query. All 6 items must exist in order for there to be a Hartford loop.

    Anyone that contends that the header or the equalizer is not a part of the design is assuming facts not in evidence. The facts are that "The Whole Thing" was thought up before there was a Low Water Cut Off, most, if not all, systems were hand fire and some systems (not all) were designed without an equalizer.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Jamie Hall
    Jamie Hall Member Posts: 21,106
    Quite so. In fact, if one really stops and thinks about what the various bits and fittings are actually supposed to do -- and are doing -- one comes to some rather odd conclusions.

    Such as... just how important is that header drip (equalizer)? Well... if you have a drop header, it's clearly mandatory. Otherwise you have a nifty place to collect any water carried up from the risers -- and there will be some -- and that's not good. But what if you have a header arrangement where the steam mains come off of the side of whatever header you have, and pitch away from the boiler? Or what if you have a bigger boiler with a steam drum and downcomers? You certainly need a drip at the far ends of the steam mains, but do you need one at the boiler? If the steam mains go up from the header, then you do... is the pressure equalization function really needed? Probably not, in reality -- but the venting/siphon breaking function certainly is, and is much better served with an equalizer than with a vent (no moving parts to fail).

    And so on. If one really starts poking into what this or that arrangement is really doing, and why, one can come to some odd conclusions about the usual way we do things...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England