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Oversized Boiler?

68GMC Member Posts: 36
Hi all,

I own a Burnham IN6 boiler, approximately 8 years old. Input 175000 btu, output 144000, Steam Sq. Ft. 450. I used <a href="">[url=]</a> to look up rad sizing, and calculated my rads to be 244.16 sq. ft. Multiply 244.16 by 240 =58598.40 Multiplied by 1.33 for piping pickup gets you 77940 btu. I am a novice at steam heat and piping, and do not know how accurate the above website is for sizing.

I would like to purchase a couple of Dans books in the next couple weeks, just to double check my arithmetic, and perhaps the above website is fairly generic, Dans EDR book might be more accurate. The rads say Taylor-Forbes on one column, Sovereign on the other column. 3 rads measure 20" tall by 7" wide, 2 columns. 5 rads measure 26" tall by 7" wide, 2 columns.

Is this fairly normal for heating guys to find for boiler sizing? Is my arithmetic close enough confidently say that my boiler is twice the size I need? What are the biggest repercussions of running a drastically oversized boiler?

Thanks in advance,



  • Oversized Boiler

    Here's another sizing chart if you want to compare the two.   As for Dan's steam books I'd suggest "We Got Steam Heat" and "The Lost Art of Steam Heating".  With an oversized boiler you're burning more fuel than you need and you should also get rapid cycling as with the extra volume of steam the pressure would build very quickly. It migh be possible to down fire the burner a bit.

    - Rod
  • 68GMC
    68GMC Member Posts: 36
    Burner Downsizing

    I read a couple other posts on this site after reading your comment, I will look into purchasing a smaller burner orifice tomorrow for an IN5. Is that something I should hire a heating contractor to install, or is it something I can do myself?

    Rod, your chart matches up pretty close to what I had found, thank you for providing it. My chart had come up with 2.0 sq. ft. per 20" tall 2 column, and 2.67 sq.ft. per 26" tall 2 column.

    Thank you.
  • Oversized Boiler

    Burners are something you want to leave to a pro as they have the knowledge, the experience and the test equipment. You might post over in the gas heating section and Tim can probably tell you what is practical for your boiler. I would then get a good burner pro to look at it for you. They are much easier to find than steam pros!

    - Rod
  • 68GMC
    68GMC Member Posts: 36

    The Burnham rep suggested a wholesaler in town here to talk to, so they could refer me to a heating contractor who knows a lot about steam. I spoke with one of their gas techs about downfiring the boiler. He suggested that the boiler was sized correctly because of the "steam chamber". He said the old boilers had a bigger steam chamber, and the new ones don't, so as the boiler fires it draws all the water out of the water chamber, and as the steam is making it's way around to the rads, the automatic water feeder (which I don't have) fills the boiler, then when the condensate returns it floods the boiler. I said "Pardon?". He explained to me, quite patiently, that "the sizing of the rads and the connected load have NO bearing on how you size a boiler". He explained that the boilers have to be bigger than the old ones because of the needed extra "steam chamber". I said "but I'm not having surging water problems, my water stays pretty much level during firing cycles". He replied "AHA! that's because its sized correctly!!!".

  • Charlie from wmass
    Charlie from wmass Member Posts: 4,195
    there is a find a pro section here

    Maybe that is a better place to look?
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • 68GMC
    68GMC Member Posts: 36
    Find a Pro

    Only works in the States, but thank you for your advice. I'm up in Ontario, Canada.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,195
    How far is that from Lenoxdale, MA?

    seems knuckle heads are going international now. I may need to get a passport sooner than I thought.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • 68GMC
    68GMC Member Posts: 36

    On whether you're flying or driving....driving its around 700 kilometres. Haha, I can't believe you'd even think of traveling that far to look at a boiler.

    I mean, I'm going to live with the boiler, it's only 8-12 years old I think, I'm doing some work on it to make it more efficient and safer. I wanted to start by knowing what the EDR load was, and whether the boiler was matched. All I wanted to know was whether it sounded like I'd done the math right, and whats the worst that could happen with a boiler thats twice the size needed. Rod suggested downfiring, and the whole thing snowballed. I have borrowed a copy of Dans EDR book, and had someone else resize all the rads, and they come up with the same numbers. It just seems stupid to be using this big a boiler. Apparently downfiring is very very bad, so my only option is a smaller boiler. 
  • MikeyS
    MikeyS Member Posts: 3
    Steam Radiators not heating up properly

    Had a boiler installed.  140,000 BTU - When the system calls for heat and the thermostat is satisfied, the radiators in the back of the house (furthest from the boiler - on the North Side) do not get completely hot.  The lower half of the radiator tubes remain cold.  If you raise the temperature of the thermostat 3 degrees, the radiators will get completely hot.  I have installed 2 Hoffman vents on each main riser in the basement to vent the air out of the main steam pipe quickly.  I have also tried a different thermostat. The differential pressure is 1 PSI and the cut-in is 1/2 PSI.   I am at a loss of what to do next?
  • Jamie Hall
    Jamie Hall Member Posts: 17,021
    It does sound...

    as though your figures are right, and that, therefore, your boiler is oversized.  The surest way to spot this, though, is observation: ideally, if your boiler is more or less the right size, your thermostat will call for heat, and the boiler will run for quite some time.  If you are not recovering from a setback, it is likely that the thermostat should stop calling before the boiler pressure starts to rise significantly.  Most, if not all, of your radiators should be pretty well hot before the boiler shuts off on pressure, if it ever does.

    However, if the boiler only runs for say 10 or 15 minutes, and then shuts off on pressure, the chances are that the boiler really is oversized.

    What are the downsides of an oversized boiler?  Primarily poorer efficiency than you might really like, plus the possible annoyance of the thing cycling on the pressure switch.  But efficiency is really the only bad one.

    Do check your pressures, by the way -- as Charley noticed, it looks like knuckleheads are everywhere, and I wouldn't guarantee that your pressures are right.

    Where in Ontario, by the way?  I used to hang out and do a good bit of work up around Peterborough and that area...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • 68GMC
    68GMC Member Posts: 36
    I will be checking

    the boiler pressure hopefully tomorrow. Tim McElwain said I need to "clock" the meter (?), test the input pressure and have the combustion efficiency checked.

    On a side note, I know it's been covered here before, but why the frick did Burnham install there plugs so blinking tight? Tim also suggested a hot water loop off the boiler, but I cannot get the blinking plugs out. I had a plumber out tonight to look at them, he just shrugged and wished me luck after trying with a 2 foot pipe wrench. I've gotten one out successfully, one snapped off head, and 2 frozen ones still.

    My boiler does shortcycle incessantly, it's quite annoying. This is the first winter I've had all the rads hooked up, I was kind of waiting to diagnose the boiler until I was sure it had a decent load on it, as was suggested to me. I have no plans to replace the boiler, I was trying to repipe it this winter/summer and improve it's efficiency, I just figured step one would be to see if it was sized correctly.  

    I'm near Waterloo now, I actually grew up about 45 minutes away from Peterborough, near Belleville.
  • Big-Al_2
    Big-Al_2 Member Posts: 263
    Quite Familiar

    I too have a similar vintage Burnham IN-6 with a similar connected load.  It behaves just as yours does.  I'll be waiting and watching to see how your improvements pan out. 

    I was thinking about downfiring the boiler, but I have three bedrooms without radiators.  When I eventually install radiators there, hopefully the boiler will become perfectly sized.
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