Replacing Steam boiler

Phillip Biston

I am going to replace my old cast iron steam boiler, I have calculated the square feet of the load at 2480 square feet of radiation (394 radiator sections @ 5 sq.ft. each and 85 @ 6 sq,ft. each) My current boiler is a H.B. smith G-400 with 8 sections and from what it looks like to me is an IBR of 4425, Am I looking at it wrong, or is it oversized?

Jamie Hall

What on earth are you heating? That's a lot of radiation! But yes, if your EDR figure is correct, that boiler is oversized.

Phillip Biston

I am heating a 4 story apartment building, I took pictures of every radiator in each apartment and luckily they are all the same type and I found them in the Every Darn Radiator book, only the few in the hallways were different but were also in the book. Thank you for your reply!

EBEBRATT-Ed

@Phillip Biston

Yes oversized. 2480 square feet of radiation and your old boiler is rated for 4425 square feet.

They should have used a 5 section at 2500 when they put that in. Would have been the perfect size

Phillip Biston

EBEBRATT-Ed said:

@Phillip Biston

Yes oversized. 2480 square feet of radiation and your old boiler is rated for 4425 square feet.

They should have used a 5 section at 2500 when they put that in. Would have been the perfect size

Thank you for your reply, I was also thinking as you said that a 5 section boiler would be the correct size, 6 section for a little fudge factor. Now my 2480 sq.ft. is just radiators not considering a pickup factor of 33% for piping, but the IBR rating accounts for that, Correct?

bburd

Correct. The IBR net steam rating includes a 33% piping and pickup factor.

EBEBRATT-Ed

@Phillip Biston

Yes as @bburb mentioned PU is included.

No need to oversize.

In addition to the boilers rated radiation capacity you have a 33% pu factor that is only needed when coming from a cold start.

Once the piping is hot the pickup factor will aid in heating the radiation

Phillip Biston

EBEBRATT-Ed said:

@Phillip Biston

Yes as @bburb mentioned PU is included.

No need to oversize.

In addition to the boilers rated radiation capacity you have a 33% pu factor that is only needed when coming from a cold start.

Once the piping is hot the pickup factor will aid in heating the radiation

I believe the pick up factor is based on insulated piping, but the uninsulated 8 inch main that runs along the ceiling near the outside walls of each bottom floor apartments is what heats the apartments. Should I use a little larger percentage pick up factor to account for this? Thanks again!

Phillip Biston

EBEBRATT-Ed

@Phillip Biston

If the piping is in the conditioned space I wouldn't add a thing. If you have uninsulated piping in a unheated basement etc then I believe @DanHolohan recommends a 1.5 PU factor

Use your best judgement

Phillip Biston

EBEBRATT-Ed said:

@Phillip Biston

If the piping is in the conditioned space I wouldn't add a thing. If you have uninsulated piping in a unheated basement etc then I believe @DanHolohan recommends a 1.5 PU factor

Use your best judgement

Thank you, since the uninsulated piping is creating the conditioned space, I am leaning towards using the 1.5 pickup factor.

KC_Jones

Why not run the numbers instead of arbitrarily picking 1.5.

The difference between 1.5 and 1.33 is 422 sq ft.  That equates to 186’ of 8” piping.  And that’s above and beyond the .33 which will support 362’ of 8” piping.  So a 1.5 will support 548’ of 8” piping in total.  For me, on a job that size, all the numbers should be calculated.  If the piping is part of the radiation, add it into the EDR and then do less than 1.33 pick up since you actually have less piping needed for pick up.

1.5 will be overkill in my opinion.

EBEBRATT-Ed

I agree with @KC_Jones

and that is what I meant to say in my previous post, though I probably didn't say it right. If the piping is in the conditioned space and is part of the radiation (and it is if it's uninsulated steam pipe)

Then you add that load to the radiation EDR load.

Any PU factor above 1.33 is only added when you have uninsulated steam pipe in a cold area ......unheated basement, garage, crawl space. If the pipe is insulated the 1.33 factor applies.

Don't forget the 1.33 is adding 33% capacity above and beyond what the radiation needs......some think that is excessive