Boiler Size - Can Anyone Confirm My Calculation

Nintzk

I am in the process of replacing my old oil tube boiler with a gas boiler and water heaters. I have had two plumbers give me estimates on the project. Both recommended Burnham boilers but they recommended different sizes. The first suggested the IN11 with 349K BTU input. I believe he chose this because input on my current boiler is 351K BTU. I think this plumber was just being lazy because, from what I have read, almost all of these very old boilers are over-sized. The second plumber did some sort of calculation and said either the IN7 or IN8 would be ok. The IN7 has an input of 210K BTU and the IN8 has an input of 245K.



I did my own EDR calculation, but this is the first time I have done this so I was hoping a more experienced person could confirm whether this is correct:



There are four 23” high tube radiators with 18 sections consisting of 3 tubes. According to an EDR chart, there is an EDR of 2 for each section. 18 sections multiplied by 4 equals 72 total sections. The total EDR is than 144.



There is one 20” high tube radiator with 22 sections consisting of 4 tubes. According to the chart there is an EDR of 2.25 for each section which equals 49.5.



There are two 20 inch high tube radiators with 11 sections consisting of 7 tubes. According to the same chart, there is an EDR of 3.67 for each section. With 22 sections that is an EDR of 80.74.



The building mainly consists of another type of radiator, which is neither a tube radiator nor a column radiator. I have a similar style radiator called a “cabinet-type radiator” and my chart calls it a "radiant convector." It basically a rectangular box but you can see that there are columns inside.



The number and sizes of these cabinet type radiators are as follows:



There are 10 cabinet radiators that are 20” and 5” deep consisting of 10 sections. There are 2 cabinet radiators that are 20” high and 5” inches deep consisting of 8 sections. This equals 116 sections. Each section has an EDR of 2.25. The total EDR is then 261.



Lastly, there are 5 cabinet radiators that are 23” high and 7” deep. One with 18 sections, one with 11 sections, two with 9 sections, and 1 with 7 sections totaling 54. The EDR sheet says each section has an EDR of 3.4. The total EDR would then be 183.6



Adding this all together there is a total EDR of 717. Does this number sound right for radiators in a 25 foot wide Brownstone that is four floors (+ one radiator in the basement)?



An EDR of 718.84 multiplied by 240 BTU (this is a steam system) equals a required output of 172,521.6 BTUs.



The Burnham Independence Series has an efficiency of 82.1%. This mean I need a boiler with in input of 210,135 BTU. Thus, the IN7 and IN8 would be enough. I am thinking the IN8 makes more sense though. I'd rather have a little more power than just enough.



Did I make any mistakes in my calculation? Do I need to factor in heat loss, the number of floors, the piping (there is one large pipe in the bathrooms which seem to provide a lot of heat)?



Thanks.

Nintzk

correction

note there is a mistake: "Adding this all together there is a total EDR of 717" should say 718.84

Jamie Hall

Assuming the arithmetic is all correct...

and the ratings assigned to the radiators are correct, you're fine.



A few points.



Don't worry about BTU.  Steam boilers are rated by EDR, which is what you have, and that takes into account normal losses (referred to collectively as pickup load) in the steam mains.  Note: normal losses.  Which assumes that all steam mains are insulated, and risers are insulated where it is possible to do so.  You needn't worry about that pipe in the bathrooms -- although it wouldn't be a bad idea to insulate it, if there are radiators in there as well.  Mains and risers were not designed to be radiators!



Boiler replacements do not take into account building heat loss, nor do you need to worry about the number of floors etc.  Just the EDR.

ChrisJ

Size

I am only a homeowner, however if your figures are correct I would go with the IN9.   The IN8 probably could work, but it would require very slow radiator venting and really good insulation of all piping and a lot of patience..  Even then, there are no guarantees.



The mistake you made was you forgot the 33% pickup factor for piping.  The IN9 is rated for 725 sqft of radiation.  That figure includes the 33% increase for piping.

The IN8 is only rated for 633 sqft.  Even with insulated steam piping you are required to have that 33%.

EBEBRATT-Ed

Calculations

The I9 is rated at 725 sq feet. This already includes the piping and pick-up factor of 1.33. That's what I would install



 because steam cycles you need to include the piping and pick up factor of 1.33 added to your radiation load of 178  sq feet and then take into account the boiler efficiency. Burnham has already done this for you as noted above the I9 will do 725 s q feet



congrats on doing your homework. All you need know is someone to install it and pipe it properly