how to measure existing radiation (Sq ft of steam) required

Al_15

I have a gas powered steam heating system in my 50 year old, 2000 sq ft home. The old boiler had 280,000 BTU/H input and 224,000 BTU/H out. The gas company did their annual review, and suggested I replace the 30 year old boiler.


I've gotten varying estimates on what the right size steam boiler is that I need for my house. Some folks say the old boilers were less efficient, and oversized, so I need less output (140 to 175k BTU/H out). Some say use the same as before.

Question: Does it make a big difference? Should I err to the smaller size or to the bigger size?

I have 14 radiators that are 6 inches tall each,(3 2-inch "squares", one above the other) and vary from 2 to 3 to 4 columns deep, and 2 to 6 sections (18 to 20 "squares" across per section each). They're 26 inches across for the 2 section, 64 inches across for the 6 section. I also have 2 radiators that are "inset"? 16 inches high by 38 inches across in 18 sections.

Is there a chart somewhere to figure out how many square ft of steam I need or BTU/H.

Thanks for your help

Thad English

Boiler size

I am not a professional (nor do I play one on TV) but I do know that in the Lost Art of Steam Heat by Dan H. (available on this website) you can find the square feet of EDR for most radiators and back into your boiler requirements that way. Most good steam professionals will not only measure all of your radiators, but also do a heatloss calculation for your house to properly determine the size boiler that you need. Chances are good that if someone doesn't do those steps that you should probably pass on their estimate and find a pro that will. Doing it right the first time will save you money to undo the wrong way. I have learned that lesson with the hugely oversized boiler in my house that the previous owners put in 4 years ago. And on friday I am laying out a nice sized chunk of cash to get it repiped so that it actually makes dry steam instead of a fine mist of hot moist air. But I digress.... you can find what you need in The Lost Art.

scrook_2

Burnham Heating Helper

Page 42 and following has steam radiator EDR tables:

http://www.burnham.com/pdfs/htghelper.pdf

Efficiency only matters for comparing *input* ratings or boilers w/ equal *outputs*, you need to determine the connected EDR in sq. ft., multiply by 240 for BTU/hr and either:

1. Match this to the replacement boiler's *net output* (DOE Heating Capacity)

or

2. multiply this number by 1.33 (33% pickup factor for steam) and match this to the replacement boiler's *gross output* (Net I-B-R Steam Rating)

The I-B-R net steam output has the 1.33 factor already built in.

As you will likely not find a boiler that exactly matches the connected load you would go to the next larger size, but the size increments are fairly small so you'd still be close.

Note for *steam*, the heat loss of the structure does not matter, the connected radiation does.

280k input and 224k output would be 80%, a new gas steam boiler would be about 81-82% for steam so the efficiency differance is not great.

For sake of arguement, say your connected load was 140k BTU/hr (583 sq. ft.) and you found a manufacture who had a boiler available in 122k (508 sq. ft.) net output and the next larger one was 152k net (633 sq. ft.) output for example, you'd select the one w/ 152k (633 Sq.ft.) net output.

Too big is not good, and there are those who argue that 133% pickup factor is probably too large for steam, if you get too small (pickup factor *much* less than 33%), or, worse, a DOE gross output *smaller* than the connected load (smaller than a boiler with *no* pickup factor) you will not be able to heat all the radiators. Somewhere between those extremes lies "just right" and near that lies an available size boiler.

Note too, MOST critical of all, you need someone who knows steam WELL to do the install -- steam systems, even more than hot water, live and die by the quality and details of the installation.

If you want to learn more I'd highly recommend buying a copy of Dan's book "The Lost Art of Steam Heating" (Everything you ever wanted to know about steam heating in one easy-to-understand book), for it truely is an art as much as a science.

http://www.heatinghelp.com/shopcart/product.cfm?category=2-3

also, just in case the Burnham Helper doesn't have your radiators (convectors?) there's: "E.D.R. - Ratings for Every Darn Radiator (and Convector) You'll Probably Ever See"

http://www.heatinghelp.com/shopcart/product.cfm?category=2-59

Even if you buy both it's short money when considered in the context of the total cost of an installed new boiler and ancillary parts.

Jo Jo

What happens to his system once it

is at full steam? If his connected load is 583 sq ft and his new boiler is at 633 sq ft, does his boiler then become oversized?

At this point ,wouldnt he produce more steam than needed? Would he shut off frequently on pressure?