EDR calcs for new Boiler, Old One Too Small?

ST140

Hey everybody - homeowner here.  I've been reading a lot regarding calculating the total EDR and BTU requirement for my one-pipe (currently oil fired) steam system.  For reference, I have used Colonial Supply's website for my tube and column style radiators (<a href="http://www.colonialsupply.com/resources/radiator3.htm">http://www.colonialsupply.com/resources/radiator3.htm</a>) and I used a link from a previous post to calculate EDR for recessed Sunray convector style radiators (<a href="http://www.governaleindustries.com/govray.cfm">http://www.governaleindustries.com/govray.cfm</a>).  This is of course because I have yet to order TLAOSH, which I will as soon as I'm finished reading WGSH.  My current boiler, a Burnham V8, which was installed in 2004 (with copper nonetheless) cracked and needs to be replaced, is rated at 356 sqft.  You'll see why I'm posting this after seeing my calculations below:



Rad 1 = 4 sections, 2 Columns, 38" Tall (EDR=4per section) = 16 sqft

Rad 2 = 7 sections, 3 Columns, 38" Tall (EDR=5per section) = 35 sqft

Rad 3 = 7 sections, 2 Columns, 38" Tall (EDR=4per section) = 28 sqft

Rad 4 (convector) = 18 sections, 20" Tall = 40.5 sqft

Rad 5 (convector) = 10 sections, 20" Tall = 22.5 sqft

Rad 6 (slenderized) = 10 sections, 3 Tubes, 25" Tall (EDR=2.33per section) = 23.3 sqft

Rad 7 (convector) = 18 sections, 20" Tall = 40.5 sqft

Rad 8 (convector) = 32 sections, 20" Tall = 72 sqft

Rad 9 = 7 sections, 3 Columns, 38" Tall (EDR=5per section) = 35 sqft

Rad 10 = 6 sections, 3 Columns, 38" Tall (EDR=5per section) = 30 sqft

Rad 11 = 8 sections, 3 Columns, 38" Tall (EDR=5per section) = 40 sqft

Rad 12 = 11 sections, 3 Columns, 20" Tall (EDR=3per section) = 33 sqft



Total EDR = 415.8 sqft

415.8 x 1.33 (For pickup) = 553 sqft



Am I supposed to believe that I'm supposed to have a steam boiler rated at around 553 sqft/steam?  Perhaps that explains why the incorrectly installed 356 sqft/steam boiler cracked in the first place?



For reference, the house is a roughly 2,200 sqft c1900 Victorian with very minimal (or no) insulation in the walls and attic.  Yeah yeah, I know, we need to insulate, but we need to get rid of knob and tube wiring before we can do so.  We weren't planning on replacing the boiler either!!!



Let me know what you think.  Thanks so much.  -Steve

ST140

Boiler

I forgot to ask - Does this mean I would probably need a Burnham IN-7 if we switched to gas (which we're considering) or a Burnham MST-513 or MST-629?  I have previous quotes for an IN-5 or a MST-396 depending on whether we want to switch or not... I assume those are too small?

Rod

Boiler- Too Small?

Hi- I guess my first  question would be: How well did the present "old" boiler heat your home? Being undersized isn't likely to cause a boiler to crack. Have you checked with Burnham? The "old" boiler may be partially covered under warranty. You might want to post some pictures of your boiler and the near boiler piping so we can see how it is configured.

- Rod

Dave in QCA

1.34 is already in the boiler EDR rating

No, you add up the EDR of your system.  Your total is 415.8 sq ft.  You size your boiler to next size larger than 415.8 sq ft Steam.  The piping and pickup is already in the boiler rating.   Unless, you have a system that has uninsulated piping in the basement, or other unusual pick up or piping loss factors.  Then you would need to add more.

ST140

Rod

Hi Rod.  If you search my username, you'll see my previous post about the current boiler setup (with picture).  I'm pretty sure those posts also address the warranty situation (we're not the original owners).  In regards to how well it heated the house - not very well.  I'm sure there are a number of different factors contributing to that, vents need replacing, boiler needs to be repiped (without copper!), etc. so I'm not sure whether it's not capable of heating the house, or if it was just installed wrong to begin with.  I'm new to the board, so I only have a couple posts, should be easy to find.

ST140

Pickup already included in IBR?

I guess I'm thickheaded and just not getting it. My EDR adds up to 415. So, I need to select a boiler with a Net IBR steam sqft rating of greater than or equal to 415? So for the Burnham Megasteam, this would be an MST-513?



I guess I'm just not getting the part about the pickup factor already being included? Included where? I've read and reread many of the posts on this site, and I'm still not getting it. I'm usually very quick with math..... Sorry, somebody please explain!!!

Dave in QCA

I know it's confusing, I'll walk you through it.

The megasteam MST513 fires at 189,000BTU.  That is the input. 

DOE heating capacity is 164,000, that is the gross output.  That is 86% efficient.  The difference between the 189,000 and 164,000 is lost up the chimney.

If you look at the NET EDR rating for this boiler, it is 513 sq ft.  We all know that steam at 2 PSI is 215 degree F.  And that a square foot of radiation at 215 F will give off 240 BTU.   Thus 513 sq ft x 240 BTU/sq ft = 123,120 BTU.  You notice that the NET rating of this boiler for steam is amazingly, 123 MBH, or 123,000 BTU. 

The radiation in a system that has 513 sq ft is capable of giving off 123,120 BTU.  In order to give off the heat, of course an equal amount of heat, in the form of steam must enter the system.  But that does not take into account the piping losses and pickup factor.  Soooo.... if you take the 123,120 BTU of the radiation x 1.333 for piping losses and pickup, it equals 164,119 BTU, and that is precisely the gross amount of heat that this boiler produces. 

Are you following this?  It's pretty simple really.



The I=B=R Net ratings relate to the system that the boiler is capable of heating, assuming that is a normal configuration and the steam mains are insulated.   NET EDR should relate your system EDR and already has the allowance for piping losses and pickup factored in. 



Do not choose the closest boiler if it is smaller unless it is very close to the same size. Choose the next size larger.  In your case, a megasteam MST396 is rated at 396 sq ft.  You have 415.8. that is only 19.8 sq ft short.  If your piping is well insulated, risers are insulated, and overall piping lenghts of your mains and laterals is on the small side, it should work fine, if a pickup factor of 1.28 was sufficient, that is about the way it figures out.

Since you have already had a boiler failure, it might be best to play it safe and go to the next size larger, even though you are VERY close to the next smaller model. 

I'm sure some of the pros will chime in on this.  I'd take their advice as gospel!

Rod

IBR Ratings

Hi -Sorry I haven't had a chance to study your past posts yet. On the IBR ratings - I have something on it somewhere but can't seem to find so I copied a page of a Weil McLain I&O manual that mentions it there and have attached it below.

On boiler sizing - If you haven't read Dave Bunnell's ("Boiler Pro") excellent and very  thought provoking article I thought it might  be of interest to you. Here's the link:

http://www.heatinghelp.com/article/11/Hot-Tech-Tips/1551/Taking-Another-Look-at-Steam-Boiler-Sizing-Methods-by-Dave-Boilerpro-Bunnell

- Rod

Steamhead

I think I'd go with the MST-513

and down-fire it a bit if it short-cycles. 

ST140

Re: Walk Thru!

Thanks for this Dave, it's making more sense to me now. I guess what makes me confused is that the steam pro I had out tonight recommended I use a pickup factor of 1.5 because of the amount of piping and level of insulation in the house. I'm feeling really dumb tonight. So... This being said, if the Gross output of the MST-513 is 164,119 BTU and my system EDR is 416, does this more or less mean there's a 1.64 pickup factor?



164,119 / 240 = 684

684/416 = 1.64



Maybe the MST-513 is too big? Based on the level of insulation on my pipes - exposed vertical pipes in living spaces going from floor to ceiling, and asbestos insulation that is incomplete in the basement, maybe it's just right? It seems like there are pipes all over the place in the basement... some insulated, some not. The house is about 2200 sqft... What happens when I add insulation to the pipes? I don't want to be burning through oil unnecessarily. And lastly, how do Thermostat settings play into a slightly oversized boiler in terms of oil consumption? Ahh, I could ask open ended questions all night long!

Werewolfx

not related to the boiler, but..

If it were me, I wouldn't waste my time removing knob and tube wiring to insulate, just insulate around it. I've serviced hundreds of knob and tube fixtures, and 98% of them are buried in fiberglass. Makes it exciting when you're looking for the knob in the dark, but that's about it...even when wet, fiberglass doesn't conduct well enough to short most knob and tube.

Mike Kusiak_2

EDR and oversizing

Yes, you are correct, with the MST-513 your actual pickup factor would be 1.64 but this is not as bad as it sounds. Steamhead's recommendation is based on the fact that you can downfire a boiler with a power burner like the MST. So you can actually fine tune and reduce the firing rate to adjust the "size" of the boiler within reason. You can also gain a little efficiency by downfiring a bit also. If you go with the MST-396, you can't really increase the firing, so if it is too small, you are basically stuck with it.



If you went with an atmospheric boiler like the IN series, you might not want to oversize as much since you can't really downfire that type of burner.



Your existing boiler was a bit lower in output than your installed EDR. Was it able to heat all the radiators fully if the system ran for a long period like when coming out of setback? Did the burner ever short cycle on pressure by reaching the pressuretrol limit?

Dave in QCA

follow Steamhead's advice

Steamhead has recommended this same boiler and adds that if you experience short cycling, to downfire it a bit.  That also may reduce the stress level on the iron and lenghten its life.

Your figures are correct.