Steam System Sizing

Steamhead

unless, as I said, pipes are uninsulated or many rads have been removed.

When you look at boiler ratings, you will see three figures:

1- Input BTU (on gas) or Firing Rate GPH (on oil)- tells you how much heat the burner will produce. To convert GPH to BTU, multiply by 140,000.

2- DOE or Gross Output BTU- tells you how much heat is available at the boiler outlet.

3- Net or IBR output BTU/Square Feet- Here is where the 1.33 is already figured in. This tells you what is available at the radiators.

So unless, as I said, pipes are uninsulated or many rads have been removed, just match the boiler's Net rating to the amount of radiation without going under, and you should be fine.

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GValente

Steam System Sizing

I read all about sizing a steam boiler and understand the concepts. I've measured all the radiators heigth, width, tubes and sections.

What is next...based on all that I have read.

Need to calculate the volume and multiple it by 1.33.

Is this correct? If yes, here is an example of one radiator's measurements. How do I figure the steam volume?

id # heigth width tubes section
1 36 8 5 9

I've added a spreadsheet of the radiator placement and measurements

Steamhead

Next thing to do

is take this info to a radiator chart, like you'd find in Dan's book "E.D.R.". This will tell you the square feet EDR rating of each rad. Since some of yours measure 36-inches high rather than the more standard 38 inches, I'll bet they're "Aero" rads made by National Radiator Co. You'll find the Aero charts in "E.D.R.".

Add up the EDR of all your rads and select your boiler using the total. Steam boilers still use the "square feet" rating which has the pickup factor built in, so there's no reason to add 1.33 or anything else to this unless a lot of rads have been removed from your system or your steam pipes are uninsulated. In the latter case I'd insulate before going to a bigger boiler.

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David Hohengasser

EDR ratings

I have Dan's EDR book. I have calculated the square feet of each radiator using the book. The previous reply said the ratings in the book have the pick-up factor for piping built in. Is this correct? I took the total square feet x 240 BTU's needed per square foot x 1.33 (pick up factor for piping). Is this correct?

Ken_8

You have not defined the purpose of this excercise.

Are you trying to see if the existing boiler is properly sized?

Are you trying to determine the correct size of a replacement boiler?

Are you trying to assess the overall design of pipe sizes, mains and boiler as a unit?

And why are you trying to convert from EDR (square feet of radiation in "equivelant direct radiation) to BTU's - and then back again into EDR?

All steam boilers are rated in EDR. The boiler's EDR outputt rating already has either 1.33 (modern method) or 1.50 (old method) pick up factor included in the data/boiler plate data stamped/printed on the boiler ID tag.

Also, there are four forms of "column/tube" type rads. It is imperative that you use the correct one. There are true "column" types in which each section's sides form what could be described as two paranethisese (sp?) that look like this: (), only touching at top and bottom; then there's the extremely old perfectly round tube type. Then there's the large cast iron tube type; then, there's the small cast iron tube type.

Then, there's sun-rad types and on and on forever...

Once again, why this excercise and do you have pictures of rads to compare what you have - with what exact style and form rads exist?

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Scott Kneeland

Sizing

I have always done the math and wouldn't size a steam boiler with out measuring the connected load. Example, I taken out a 6 section Arcoliner that was aroung 600 sqft IBR and in what looks like a HUGE house and when all was measured I only needed a 265 sqft IBR boiler. Its been thru 2 New England winters with the new boiler and heats great and saved almost 30% on fuel. The numbers don't lie.

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David Hohengasser

Boiler is oversize

The boiler is rated IBR 470 sft. Measured radiation required (using Dan's book) is 320 sft. Should I consider a new boiler? Previously there was only 167 sft attached to this boiler for 13 years. My gas bills were very high and boiler short cycled. The other boiler (40 yrs+) finally rotted through so I am connecting that load to this boiler. That is where the 320 SFT comes from. Is 32% oversize still a concern for efficency reasons?

Steamhead

It shouldn't be too bad

and if it is, you can down-fire it slightly.

If you're considering replacing both boilers, why not get two smaller ones, matched to the load they will handle? This will let you zone the system.