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How much can I down fire a Weil McLain SGO-4 oil fired steamer?

V8toilet Member Posts: 71
We have an SGO-4 boiler that came with the house we bought and its too

big for the radiation in that house. The house has 362 sq ft of

radiation in it and a Weil McLain SGO-4 boiler supplies 450 sq ft of

steam. Buying a new boiler is not an option this year (an SGO-3 would be


my options are add more radiation to some of the rooms that don't have

any like the half bath and laundry and maybe basement and also down fire

the boiler.  The question is how much can we safely down fire this

boiler without causing more problems.

We will have a licensed oil man down fire it for us its just that I like to have as much expert information as I can get.  

Thanks in advance.


  • Steamhead
    Steamhead Member Posts: 16,723
    Well, if those rooms are too cool

    they'll need radiators. Add these first and see how it does. Size your rads to the rooms' heat losses.

    Most boiler makers don't recommend down-firing. I would not go below 80% of its normal firing rate since it might run too cool and take forever to make steam.

    Try the added rads first.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Al Letellier_21
    Al Letellier_21 Member Posts: 402
    downsizing boiler

    If the boiler really is too big, why not downsize it. The great thing about Weils is how easy they come apart and we have either upsized or downsized them many times in my career.....a new jacket is a lot less money than a new boiler. I have been told by Weil that 25% is max for downsizing the nozzle. Also, a SGO-3 will be slightly undersized as it is rated for 354 sq feet.
  • Ron Jr._3
    Ron Jr._3 Member Posts: 603
    A new jacket

    and a new flue collector too , unless you use the back flue outlet and jury rig a top blank plate .

    I've always thought you can downfire a boiler as low as you want , as long as the flue gas temperature is high enough to prevent condensation ? But more than likely the 20 to 25 percent figure is dead on for that reason . Just downfired a cast iron boiler from 1.20 to .70 yesterday . Stack temp was 375 after the change .
  • V8toilet
    V8toilet Member Posts: 71
    Thanks for the help

    Thanks for the replies. I was wondering if we could remove a section after the heating season is over to make it essentially an SGO-3 sized boiler?

    I was reading through Dans book "lost art of steam heat" and he mentions that on jobs where the insulation has been removed he uses a 1.5 pickup factor instead of the 1.33 pickup factor to size a new boiler. If we leave the insulation off the pipes and use the 1.5 pickup factor than with 362 sq ft of radiation we have * 240= 86880 btu *1.5 = 130320 btu (543 sq ft). The boiler has a DOE rating of 144000 btu (600 sq ft) so if we add 57 sq ft of radiation or downfire the boiler 10%, we would be right where we need to be.  This will get us through the heating season until we can fix it right next year when we have the money and time.

    The boiler has a 1.20 gph nozzle now with a Becket burner, How much would we have to reduce the nozzle size to reduce the boilers capacity 10%?
  • Paul Fredricks_3
    Paul Fredricks_3 Member Posts: 1,557
    not too much

    Drop the rate too low and it will be like a match: Very hot, but not enough heat to get the steam going. The amount of heat is the key. It's not just temperature, but the volume of heat. I was once told that an iceberg has more heat than a match.
  • Paul Fredricks_3
    Paul Fredricks_3 Member Posts: 1,557

    The only thing about that is a lot of condensate running back to the boiler, creating wet steam. and those heated pipes radiate heat into the basement, which rises through the floor. Could over heat the first floor. Unless that's where the thermostat is. If that's the case it could keep the second floor from getting heat. I don't remember if you have 2 floors there.
  • icesailor
    icesailor Member Posts: 7,265

    I'm not an "Expert" on steam but,

    As I understand it, steam likes to have a large area to steam in and let the steam flow into the system. A SGO-4 boiler isn't very big and a SGO-3 is even smaller. In the case of a steam boiler, I don't think that removing a section on this boiler is a brilliant idea. That boiler is fired at 1.20 GPH. That is a maximum firing rate. I have actually found that with Carlin EZ-1's, they give the best burn efficiency at their maximun firing rate, But when downsizing the nozzle, 1.10 GPH is the next nozzle. They run efficiently with this combo. The SGO-3 is rated to fire at .95 GPH but most are fired at .85 because that nozzle is what is freely available.

    If you are worried about cost and efficiency, I would make sure that ALL supply and return pipes are WELL insulated. You will save more money from insulation than you ever will by playing around with downsizing the boiler.

    Steam boilers are different animals than how water boilers.

    Just my opinion.

    I have a W/M WTGO-3 and for the cost at installation and cost of operation, I wouldn't change it for anything.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,314
    The piping is where the steam goes not the boiler chamber.

    If you need to severely down fire to match the load and the piping is up to specs for the load then removing a section saves fuel. It means less square footage to heat the chimney when the burner is off.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
This discussion has been closed.