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Hoffman differential loop but no Hartford loop

Hi all
Brought out house three years ago and love the fact that we have a really good steam heating system with radiators
All the radiators have Hoffman #7 inlet valves and Hoffman #8 steam traps
In the basement the boiler looks to be a 1980’s replacement it oil to steam Burnham
We get no hammer or other issues except the system seems too me to use a lot of oil
I have the boiler serviced regularly but local help with the rest of the system is very limited, we live in Amesbury MA
What has me raising a question here is if I should expect to see a Hartford loop at the boiler to go along with the Hoffman Differential
I have some other questions
What boiler would be best suited as a replacement
Is it reasonable to go to Gas to steam
Would a pressure vented gas boiler be an effective choice the current boiler vents into the chimney which is not lined and in poor shape
Does anyone know where you can buy secondhand Hoffman #7 valves I want to work through restoring the valves but want some spares on hand before I start
Thanks for any advice


Pete

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 9,700
    No a fan of Burnham but that;s just me, others like them. I like Peerless. Gas to steam is fine, you may have to put in a chimney liner. Make sure to total up the EDR of all the radiation. Don't just size the boiler based on the old boiler.

    I wouldn't repipe the old boiler to put in a Hartford but if you replace it I would put a Hartford in. It will do no harm
    ethicalpaul
  • Jamie Hall
    Jamie Hall Member Posts: 16,605
    The Hartford Loop and Hoffman Differential Loop serve entirely different purposes. No harm to having one without the other.

    That said, the presence of the Hoffman Differential Loop, the #7 valves (good luck finding them -- wish I had a spare or two...) and the #8 traps indicate that you are the proud owner o a Hoffman Equipped Vapour system -- a very fine example of vapour systems which, if treated with some care, will give superb service.

    That said, note that I said up there "some care". They often get knuckleheaded. First, check at the ends of the steam mains. There should be crossover traps -- probably also #8s -- from the steam mains to the associated dry returns. It's not that uncommon for some bright child to have taken them out and substituted vents. Put them back if they are missing. They are essential. There must be no vents anywhere on the system except on the dry returns right at the Differential Loop. Second, all the dry returns must join together at the boiler, and then be provided with vents and go into the Hoffman Differential Loop. Well meaning folks may tell you that they need to drop below the water line, then tie together -- and they'd be wrong. Third -- and easiest to correct in some ways -- the Hoffman Differential Loop is designed and intended to limit the pressure difference between the steam mains and the dry returns to 8 ounces per square inch or less. To that end, a modern boiler (and, by the way, gas or oil it doesn't matter) must be controlled by a vapourstat, set at a cutout of 7 ounces per square inch or less. This is not optional! I would suggest that the pressuretrol, if you have one, be kept and the vapourstat be mounted separately.

    The venting at the Hoffman Differential Loop need not be all that much, usually -- unless your system is really large, 2 Gorton #2s on an antler will be fine -- but if you already have a Hoffman #75 or #76 there, you can just supplement it with one Gorton.

    Part of the reason the system seems to use too much oil may be that it is running at too high a pressure. The Hoffman Equipped System is marvelous, but if you overlook the caution on pressure the loop will trip -- and that will pretty well stop the system from heating until it recovers, during which time you are burning oil to much less effect.

    On the new boiler -- make sure that it is properly sized. No bigger a boiler than needed to match the EDR of the building, and preferably up to 10% smaller. Also, make sure that it is properly piped. The Hoffman Differential Loop has a connection from the header or a very nearby steam main, and that has to be there. An unwary plumber may well ignore it, to your cost.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Steamhead
    Steamhead Member Posts: 14,766
    @peteroneill3 , my partner @Gordo can fix those #7 valves. He did two of them just a couple days ago, on a Hoffman system that one of the larger local contractors had knuckleheaded. Amazing how well they heat with working valves and a Gorton #2 replacing a Hoffman #4A as the main vent..............
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • dopey27177
    dopey27177 Member Posts: 717
    Jamie hall hit right on the noggin.

    Be wary of any new boiler installed. The water content in them is much smaller and yo may need to know how much water is boiled off per minute. (Because) If the boiler shuts down on low water because all the condensate did not return quickly enough and the burner will not start until the proper water level in the boiler is reestablished.

    There are two remidies for this condition,
    1 install a condensate pump
    2 modify the return piping system

    Jake
  • peteroneill3
    peteroneill3 Member Posts: 5
    edited November 2020
    Gentlemen thanks for your advice and information
    Can is ask (I do not doubt the need but I am curious) if the original vent was a single Hoffman No6 why now do I need to change the vent, I’m sure there is a reason just curious
    The house is quite small 1800 sq ft with 9 original radiators and one small additional radiator in a toilet
    The no 8 traps are still in place in the crossovers
    I suspect they have not been serviced for a very long time so I will plan to service them next summer, I have read Dan’s warnings about undertaking this as a home owner what’s the sage advice here, if I can’t find a local steam guy who I can trust do I take the risk, I will check the temp differentials over the next few weeks,
  • Jamie Hall
    Jamie Hall Member Posts: 16,605
    The old Hoffman #6 may have been adequate, if the original system was coal fired. However, it is a very small vent, relatively speaking ( @gerry gill 's data show it would take 10 #6s to equal one 76, never mind a 75). So... no, it's really not adequate. The reason is that a gas or oil fired boiler develops steam much much faster than a coal fire starting up.

    Check the traps for operation before you start taking them apart. In a vapour system, if they haven't been abused, they may be just fine. What you are looking for for the crossovers is that the steam main heats quickly, and the inlet to the crossover gets hot -- but the outlet stays much cooler. If the main is slow or very slow, the trap may be failed closed. If the outlet gets steam hot, it's failed open. Either condition needs to be repaired -- but new innards are easily available.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • peteroneill3
    peteroneill3 Member Posts: 5
    Thanks again Jamie my concern will be how to fit more vents especially if they are taller than the old Hoffman no
    6
  • peteroneill3
    peteroneill3 Member Posts: 5
    edited November 2020

    Btw what’s this
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 9,700
    @peteroneill3
    That is a check valve. It allows flow in 1 direction only and will stop a backflow. In your picture flow is from left to right
  • peteroneill3
    peteroneill3 Member Posts: 5
    @EBEBRATT-Ed thanks
  • Jamie Hall
    Jamie Hall Member Posts: 16,605
    Um. That vent installation isn't very helpful, is it? What is the total available height from the bushing in the top of the Loop to the ceiling -- which, I presume, is also the subfloor above? Might be able to fit a Gorton #1 in there...

    At this point you need a low pressure gauge on the boiler, to find out how badly you really do need more venting. You may not. What you need to do is -- with the low pressure gauge -- see how the pressure in the system behaves as you fire the boiler from a cold start. If the pressure rises to something reasonable -- say two or three ounces per square inch -- and stays there for a while (until most of the radiators are mostly full), you're good to go. Otherwise we need to do some thinking...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England