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# Clarification on steam boiler sizing

Member Posts: 18
In sizing a steam boiler, I have calculated the EDR of all the radiators.This particular house has 58ft of 2" uninsulated main, which they dont want insulated for fear of freezing in the basement. The connected load also includes 110 ft of 1 1/4 runouts.

Should the load calculation include these piping losses, even before addition of any pickup factor?

The pickup factor in my understanding is to allow for the heating of the total load from a cold start, but this extra load is a continual load, no different than additional radiators or bare pipe used for space heating.

Where can I find equvalent EDR of 2"&1 1/4" bare iron pipe to add in the calculation.

I own all of the steam books available thru heatinghelp and cant find that particular info.

But let me take a minute to point out the quality of the books on the site. Some of the best refernce material for steam heat available. Worth every penny.

• Member Posts: 194

But I believe the pickup factor accounts for the piping as long as the edr for the rads is accurate.

This is how I sized my boiler.
• Member Posts: 4,406
EDR of pipe

The boiler sq ft number includes a pickup factor of 1.3

2" pipe has an edr of 8.75 per 10 feet; 1-1/4" pipe has an edr of 6.25 per 10 ft of bare pipe. Your 2" pipes would have a total of 52 while the runouts would have a total of 69.

Bob
Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
Vaporstat with a 12oz cut-out and 4oz cut-in
3PSI gauge
• Member Posts: 6,653
And just a bit more clarification...

If you leave those steam mains uninsulated, they are NOT included in the pickup factor, and MUST be included in the total EDR for sizing your boiler.

I am not in favour of using uninsulated steam mains to heat a space; doing so tends to lead to poorer steam distribution and slower heat elsewhere, if nothing else.  If you do go this route, be aware that there will be a lot of condensate in those mains; you need to size and slope them as though they are one pipe steam, either counterflow or parallel flow as the case may be, with the total EDR of the pipe connected at the worst possible end of the line (far end for counterflow, near end for parallel), and be generous on the sizing -- if it were I and I had to do that, I'd go one pipe size up from whatever the calculations suggested I needed to  use.
Jamie

Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
• Member Posts: 1,660
edited December 2013
teeny weeny itsy bit more clarification

Technically speaking, the 34% pickup factor is actually two separate factors added together, usually stated as piping and pickup factor. It consists of 15% for piping losses and another 18-20% pickup factor to allow for even distribution of steam on a start-up due to the inherent characteristics of steam systems, particularly cast iron steam systems. The two are rounded off to 34%. Dan suggests using 50% when the mains are not insulated.

All of this reminds me a little bit of a Boiler Chemical Rep that serviced my account many years ago. His favorite phrase was, we tend to measure it with a micrometer and cut it with a chainsaw.
Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
http://grandviewdavenport.com
• Member Posts: 333

For argument sake, say a boiler steam rating is 500sf, and attached radiation is 500, not including piping, does boiler rating of 500 have hidden pickup factor of piping in 500 sf figure?
• Member Posts: 1,035
Pick Up Factor

Yes, the pickup is the difference between the Net EDR and the Gross Output of the boiler.
• Member Posts: 18
Ah, Clarification Achieved...

Now it becomes clear.

X 240BTU= 82,560 BTUH

The Mains and Runouts (Uninsulated, in cold basement)

2" =52sqft EDR X 240 = 12,480 BTUH

1 1/4 Runouts = 69 sqft EDR X 240 = 16,560 BTUH

Total Piping Loss= 29040 BTUH or 121 sqft EDR

Total Load= 465 sqft EDR = 111,600 BTUH

PickUp Factor (.34) 158 sqft EDR = 37,944 BTUH

Total 623 sqft EDR = 149,544 BTUH

BTW Single pipe parallel flow upfeed system, single 2" main, 1 1/4 return off the end of the main.

Existing boiler ratings (New replacement 2 yrs ago, Immediate issues since)

Boiler Model MST396SL-HB

Firing Rate 1.05GPH

DOE Capacity-127 MBH

NET IBR- Steam 396 SQFT

STEAM-95 BTUH

So my assumption is that by taking the net rating of 127000BTUH and dividing by 240BTU/SQFT EDR, the boiler is rated at 529 sqft EDR, including pickup factor.(Since removing the .34 factor, gives me the 396 sqft EDR NET IBR rating.

So, without pickup factor, the boiler rating at 396 EDR is undersized for the load of 465 EDR.

With the pickup factor, the boiler rating of 529 EDR is undersized for the load of 623 sqft EDR.

Even if the piping is insulated, it wont remove the piping losses, just decrease it.

I don't see it lowering the load below the max rating of the boiler. This boiler seems like it was undersized for even the best case scenario.

We've been working on venting, re pitching wandering up&down returns, but with the heavy condensate load, the undersizing etc, I don't know if that last radiator will ever get hot, or this system will ever behave.

Last night, a no heat call bc I has dialed down the press from 5 psi to .5/2.0 and behold, boiler shut down and held at 2psi bc the condenstae backed up and held it off.
• Member Posts: 1,660
edited December 2013
what type of 2-pipe?

Common system types were Moline, Dunham, Trane, Arco, Hoffman, etc. Most were intended to be operated at 8 oz or less. Some of the systems, (Dunham) are inherently unbalanced without orifice plates in the inlet valves.

I have a 1910 Dunham systems that was impossible to balance. I discovered that "regulating plates" were originally recommended by Dunham. After installing plates purchased from Tunstall, the system operates great!! Really Really Great!

Remember on your return line, that 1 psi in the boiler equals 30" water column, so if you have 2 psi in the boiler, the returns will stack up 60" and if that is as high as the lateral return piping the boiler will push water out the return and up into that piping. Many times condensate pumps were added. Some original systems had a return trap that used steam from the boiler to equalize the pressure in a small vessel and allow the condensate to return by gravity.

Please post pictures of your boiler and near piping, also supply valves and traps on the radiators.

First thing, turn down the pressure, you will probably need a vaporstat to control it low.

Also, in your calculations, you are still double counting the piping. The normal piping and pickup factor of 34% includes 15% for piping losses and about 18% for pickup. So, if you actually measure your piping losses, you would not use 34% top of that, you would use 18%. According to that, it appears that your boiler is not oversized. I have a hunch that the problems lie elsewhere.
Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
http://grandviewdavenport.com
• Member Posts: 18
Still undersized?

Based on the IBR of 396sqft EDR, and measuring the piping losses with a pickup factor of 18%, I come up with a need for 548 sqft EDR. This leaves me 152sqft shy, and undersized of almost 30%, unless I'm missing something....

I'll take some more pictures so I can get them up fo viewing.
• Member Posts: 1,660
edited December 2013
Calculations

Your Boiler DOE output = 127,000 BTU

Your Radiation = 82,560 BTU + (18% Pickup factor) 14,861 + (actual piping loss) 29,040 = 126,461 BTU. Your boiler DOE output needs to match this or slightly exceed, which it does.

Using Dan's method of a 50% piping and pickup factor for uninsulated pipes,

82560 BTU + (50% piping and pickup factor for uninsulated pipes) 41,280 =123,840 BTU. Again, this is less than the output of your boiler.

In your post, you said, "So my assumption is that by taking the net rating of 127000BTUH and dividing by 240BTU/SQFT EDR, the boiler is rated at 529 sqft EDR, including pickup factor.(Since removing the .34 factor, gives me the 396 sqft EDR NET IBR rating."

That is not correct, because the Boiler EDR rating is only a calculated number, based on the DOE output and reducing for the the piping and pickup factor. It is there to aid in matching the boiler to a system without having to do all of the calculations. 127,000 BTU is not the NET, it is the DOE output, or the Gross Output. If you take a calculated Boiler EDR rating and remove the piping and pickup factor, then it is no longer the Boiler EDR rating. Not sure what it is...

Do I understand correctly from another post, that you are saying that the system builds up to 2 psi and you still have no heat in one of the radiators? If that is the case, then there is something else wrong. If your boiler has the ability to build 2 psi pressure in the system, it is NOT undersized.