boiler sizing

joe7

Good evening.  I'm looking for immediate guidance to size my new boiler.



Here is the info I have (please correct me if I'm calculating it wrong):

the EDR of my radiators = 472 edr

add 33% (for pipe pickup (if I understood it correctly)) = 627 edr

* 240 = 150,662



I had 3 plumbers give me estimates.  Each one is suggesting a different size boiler.

The 3 choices were all Burnham:  IN7, IN8 and IN9.

question:  which one should I get?



(The boiler is in an unfinished basement.  There are 2 mains: 1 runs 25', the other 50'.  75% of mains are insulated with 1/2" fiberglass. The house is 20x80 detached on 3 1/2 side).   Do I go by DOE or I.B.R ratings?

KC_Jones

No need to add pick up

If you add up the square feet of radiation you can use that number to directly size the boiler.  The manufacturers already add in the pick up to their ratings.  If you look at the product brochure they list the sq ft of radiation to make it as simple as possible.  I am including a link to the Burnham brochure you can see the ratings for those boilers on page 2.  For your 472 sq ft of radiation the IN7 would be more than enough you are actually really close to an IN6, so the IN7 should be more than enough for you.  I am not a pro, but I am sure a few of them will chime in on this as well, seems to be a fairly common question.

https://file.ac/etji_kkpBKc/independence-product-data-sheet.pdf

EzzyT

EDR

Did the pros that gave you estimates size boiler up right by getting a EDR load from the radiators or did they just take that info off the existing boiler rating plate? Yes you go according to the square footage as kc as mentioned the pick up factor is already added in by the manufacture. If that EDR is right at 472 you can get away with the IN6 those 22sqrft aren't going to show that much of a difference in the over all way the boiler cycles you wanna get as close as possible with sqrft of the boiler to the EDR of the system never wanna go to big. The next step is making sure the boiler is piped correctly and the system vented properly too. The header should be at least 3" using both supply tappings on the boiler if I was piping the boiler it would be a 3" drop header 2" equalizer all piping done in black steal pipe with steam cast fitting no copper

KC_Jones

Make sure you trust the contractor

This is something that is mentioned by the pros over and over.  If they don't make you comfortable then move onto the next guy.  They should talk to you about what you want comfort levels complaints about current setup, there should be a lot more to it than just here's your boiler pay me.  You are buying a contractor as much as you are a boiler.  Research on this site and even buy Dan's books if you feel inclined, I did and can tell you first hand they are fantastic and will educate you a lot about your system.  Being an educated consumer is always a good thing.  There are a lot of fantastic contractors around, but also more than a few "knuckleheads".  Good luck and I hope everything works out for you!

joe7

IBR vs DOE

question:  are the IBR and DOE rating practically the same thing, only one includes the 'pickup factor' and the other does not?

IBR x 33% = DOE? 

if this is true, than I would either use my radiator EDR and than go with the IBR rating or add 33% (pickup) and go by the DOE rating?

KC_Jones

Don't need to do all that math, but...

the DOE rating is derived from the efficiency of the boiler.  So if the boiler has an input BTU of 100,000 and it's 80% efficient then the DOE rating is 80,000.  The IBR is minus the pickup factor so you can use the radiator calculations exactly as is.  So for the above boiler with a DOE rating of 80,000/1.33=60,000 IBR.  So if you had 250 sq ft of radiators X 240 = 60,000.  If you want to calculate your own pick up factor other than the standard 1.33 multiplier then yes you would go by the DOE rating.  So taking the above 250 X 240 X 1.33=79800 which would equate to the DOE rating of 80,000.  If you thought you needed a different pick up factor then you could use a different multiplier and use the DOE rating to size the boiler, if you are that confident.  Hope that helps.