sizing steam boiler

[Deleted User]

Please help me understand sizing steam boilers.  I read Dans book lost art of steam heating and measured all radiators at job.  Got the height, # of sections and tried to figure out how many columns it was.  That confuses me, do you count each section of steel on the side as column just like you would a section? Next I kind of understand converting it to sq feet per section than I get confused.  If I multiply the number of sections with the sq feet per section.  Than multiply that by 240???  Im not sure if Im doing it right it seems as if my calculation is off please help.  Thanks Mike

jpf321

yes and no...

yes, columns are the vertical pieces front to back. both the new copper

rads in this post

(http://www.heatinghelp.com/forum-thread/132573/Reducer-bushings/success)

and the older connected rad in "room 2-A" are 3-column rads. They have a

front column, a back column and a middle column .. some rads have more

that 1 "middle" column.



now, all you need to do is obtain the sq ft (you can obtain the BTU if you like too but...) most Steam Boilers will have a specification for SQ FT of steam they are rated for.



So get the SQ FT for each rad, add up all your rads and find the total SQ FT. Then find a boiler spec chart such as Page 8 here: http://www.slantfin.com/documents/237.pdf and find the SQ FT column .. read down and there you go .. at least this is true of most residential boiler spec sheets.



However, yes, if you multiply the total SQFT by 240 then you get total BTU .. however then you have to worry about being confused by pickup factor, BTU IN, BTU OUT, that gets confusing, so just look for columns labeled SQ FT STEAM and compare it to your calculated radiation load numbers. (Columns, Sections, Height, etc.) ..



a little hint, if you have any recessed "radiant rads" they are 1 SQ FT for every inch wide .. just measure the width and you have the SQ FT.

SteamHeat

One Other Detail...

One more thing I would add to jpf321's excellent answer.



The sq ft ratings of modern boilers use a piping and pickup factor of 1.33



That assumes some degree of pipe insulation on the sections inside your walls.



If you live in an old place that has no insulation, you'll want to use a piping and pickup factor of 1.5 to 1.6 instead and so you need to recalculate the boiler sq ft ratings yourself. If you don't the boiler will be a little undersized and will take longer to warm up your home. I lived with this for a while and it was no fun at all.



Hope this Helps

jpf321

yep ..

let's take the TR-30 example on Page 8 of the document above ..



Rated @ 421 sq ft.

421 x 240 = 101 MBTUH (MBTUH = thousand btus/hour = MBH)

101 MTBUH * 1.33 (pick-up factor) = 134 MBTUH



If you look at the other columns of the chart, you will see that all of the above RED numbers are there. As well, you can read the footnote regarding 1.33 Pickup factor.



So, if you have for example 390 sq ft of installed radiation but you have non-insulated pipes, lots of crazy piping, hot water loop, tankless coil, and other things that may make things hinky and decide on a 1.5 pickup-factor .. then: 390 x 1.50 = 585 BUT YOU CAN'T USE THE COLUMN LABELED SQ FT ANYMORE, BECAUSE THAT COLUMN ACCOUNTS FOR 1.33 PU-FACTOR ALREADY .. you need to instead .. 390sq x 240btu x 1.5puf / 1000convert-units = 140 MBH and use the D.O.E. Heating capacity column .. you'd be somewhere over the TR-30 and under the TR-40 .. that's when you come here and you discuss it with a seasoned pro to decide which way to head.



By the way, if you used the 585 improperly calculated in the last paragraph and looked at the sheet, you'd end stuck between a TR-40H and a TR-40 .. which would actually prove to be slightly oversized (numerically speaking anyway). You'd also be paying more for a 40series than a 30series boiler (well at least if you were purchasing it yourself). Last note here, the TR-20 is 2-section, the TR-30 is 3-section, I bet you can guess what a TR-40 is ..



so if a plumber comes to your house and says "You need a 5 section boiler in here to heat this old house." First you ask him, "How did you come to figure that Joe?" ...There is only 1-right answer with a steam system and it's the reason you started this thread :-) Any other answer "that's what I always install", "your old boiler spec'd at this size", "you have 3, 4, 5 stories here" etc. and you don't call him back again.



Then you ask him "what brand were you thinking about for me?", and after he leaves, and before you sign anything, you find that boiler and do the math. Often times, plumbers will come in talking about sections. I think the same maybe true of other brands, the Peerless EC3 maybe a 3-section, a Burnham IN6 could be a 6-section .. but I'm just guessing on this .. but you see what I'm getting at.



Also keep in mind that pickup factor comes into play biggest before all the piping heats up.. once all the pipes are steamy hot, pickup factor is less at play. So maybe you could lean toward the smaller TR-30, but again the final decision is a question for a seasoned pro that has real world experience with many different configurations.

Rod

EDR Survey

Hi- Here's a radiator sizing sheet that might be of help to you.

- Rod

SteamHeat

Two More Considerations...

One other thing to consider is how the boiler block will get into your home. If your doorway and stairway are narrow, you will need a knockdown boiler (boiler that needs to be assembled once the parts are brought in). Not every brand comes as a knockdown.



The second is your chimney large enough diameter to properly exhaust the size boiler you decide on. If not you'll need (possibly a liner removed), a roto hammering and a larger liner.



Hope This Helps More Than Confuses :-)

jpf321

i stand corrected

You cannot convert reliably from Boiler Spec BTU to SQ

FT of steam. Because vessel volume matters ... and different brands have

different vessel volumes.







Consider for a moment that your vessel only held 1 cup of water .. you

could heat it with 2million BTUS but you would never get more than a

cup's worth of steam sq footage.







As I said at the outset, once you stray from that single column on the

boiler spec sheet "STEAM SQ FT" things get very confusing. It's best to

work with only that column and if you feel that pickup factor is a

substantial issue, leave a little bit of steam spec'd sq ft extra.

SteamHeat

Easy Conversion...

If you use the sq. ft. column for the standard piping and pickup factor of 1.33 in boiler literature,

and you want to convert the values to a piping and pickup factor of 1.5,

just multiply the number in the column by 1.33 / 1.5

jpf321

i think what you are saying ....

mutliply by 1.33 then divide by 1.5 .. yes that will give you a proper number ..



S/F TR-30 = 421 rated (including a 1.33 pu factor)

421 * 1.33 means it is capable of producing 560 sq ft ..

560 / 1.5 means that the new rating using 1.5 pu factor is 373 sq ft ..



rated 421 sq ft @ 1.33

rated 373 sq ft @ 1.50



I realized this the other day as well. Thanks.