one boiler,two risers,one main-question.is that more efficient? twice the steam,4 same fuel burn

LS123

hello all,

i was looking at some steam heat you tube clips and ran in to one of @DanHolohan s clips. it was titled "Near-Boiler Piping in Steam Heating Systems"

one of the things caught my attention was one steam boiler, two risers, and one main supply line. pics below. Questions first. just to satisfy my curiosity...

1) is this type of configuration of steam system more efficient?
2) would this system configuration, Burn same amount of heating fuel and distribute more steam? twice the amount of steam?
3) Would this config. be available for residential steam systems?
4) What brand of residential boilers would come with two risers that would allow to have this config?

thank u!

EBEBRATT-Ed

Every boiler mfg is different. It depends how thick they make the front and back sections. Obviously you couldn't put a 4" riser in a section 3" wide.

So, depending on the output of the boiler some Mfg's may use 1, 2, or 3 risers for the same capacity boiler

For a given size output from a boiler the # of risers would probably not affect the efficiency in a measurable amount. Just look for a boiler that is known to be a good steamer. Many will use Weil McLain, Slant Finn or Peerless with good results and their are others. The general consensus seems to be to avoid side out boilers on steam and at least follow the MFG minimum piping requirements

LS123

thank you @EBEBRATT-Ed !

Jamie Hall

Many larger boilers use two (or sometimes more) risers. There are two main benefits. The first is that it leads to a more uniform water level in the boiler; the velocity of the escaping steam tends to draw the water towards the riser, and if there is only one riser in a larger boiler the water line gets "tilted". Not a really big deal in most residential size boilers. The other is that for a given riser size, the steam velocity will only be half as great with two risers as it is with one, and this leads to less carryover of water droplets in the steam, which in turn makes it easier to get dry steam out of the header.

So that's really addressed to your number 3. As to your number 4, many larger (and some smaller!) residential boilers come provided with tappings for two risers. In some cases -- side outlet boilers particularly -- it's almost mandatory that both be used to get decent steam quality. In others, the steam quality is affected at least as much by the header configuration.

The amount of steam produced by a boiler is determined almost entirely by the rate at which heat is provided by the burner. The number of risers has nothing to do with it.

As to efficiency, that is partly affected by the number of risers -- but at least as much, if not more, by the overall geometry of the near boiler piping, provided only that the steam velocity in the riser or risers is not truly insane. A properly designed and piped header arrangement, however, is really important. Some water will almost always be carried into the header -- some boilers more than others -- and the job of the header is to slow the velocity enough, and arrange the turns correctly, so that the water droplets fall out of the moving steam and stay in the header, to be conveyed back to the boiler through the equalizer. This means that the header should be at least one size larger than a single riser, or two for two risers, and that the flow of condensate and steam in the header always be the same -- no meeting flows or counterflow conditions.

LS123

Br. @Jamie Hall ... thank you so much for this wonderful, insightful detail oriented explanation. I am learning a lot from the forum.

Although my boiler is 70+ years old, it seems to have two openings for two risers on the top of the boiler connecting to the heat exchange. I have no plans to change the config since it works almost perfectly. one opening is closed, the other has about 2 and 1/2 inch riser about 2 feet tall. then riser is connected to one main supply line via elbow of the same size and main supply line is the same size. I do not know all the terminology, in a single pipe system like mine do not have a header. I am assuming riser being two feet tall, correct firing rate keep water getting to the main supply line. Would that be a correct assumption?

Thank you again and best!

EBEBRATT-Ed

@LS123

Old boilers by today's standards look like they are piped wrong, but they were designed differently. When the newer energy regulations came in everything changed

LS123

Thank you! @EBEBRATT-Ed ... i have lot of free time these days... I am naturally curious... After I finished watching the near pipe boiling clip from Dan H... I could not figure out how the two risers worked and the efficiency.... So I had to ask

Absolutely agree with you... when I look at my old boiler that still works and heat the house so well, I can understand what most things do in general terms.... when I look at new boilers... I take a deep breath, scratch my head... then try to figure out, most of the time get stuck...

The I find the answers to my questions in the HH forum members.

Thank you and best!