pipe sizing out of boiler

John B_2

What size piping would I use coming out of a 2 inch supply at boiler. I mean when does it get reduced? Right away, or after the air separator? Not sure how to size this.

Brad White

You can

size it based on your normal flow rate and components.  If your air separator is larger than your running pipe size, start there and reduce afterward if you need to.



What is your BTU rate and system design temperature difference?



(If your load is over 250 MBH, then heck, you may need the 2", but somehow, I doubt that very much!)



The reason that you probably have so large a tapping is that the casting might have been for a "Steam Or Hot Water" boiler, so one casting and machining process allows an installer to bush down in the field.

John B_2

input btu is 250,000. I want to know this because I dont know

what size air scoop to get. Highest temp will be 180 out 140 return if that is what you were asking about.

Brad White

Ah, I see

A few preliminaries which may not apply to you.



1) Do you know the heat loss of your spaces? And how the boiler size relates to that?  Boiler size and radiation is not heat loss.



2) If the boiler is over-sized, well regardless if it is or not, you may want to consider decoupling the boiler, make it on its own circuit and have the radiation on its own circuit. In this way, you can keep the boiler at higher temperatures to protect it and "sip" water to vary the temperature where it really counts, at the radiation. Might you be doing this already?



But this is getting beyond your immediate question, so here goes:



A boiler at 250 MBH input likely has an output of  200 to 215 MBH or 20 to 21.5 gpm flow rate if using a 20 degree temperature drop. That is right on the edge of using a 1.5" or a 2" pipe. Being conservative, I would go with the 2" exiting the boiler and save a bushing. Then I would reduce to 1.5" or 1.25" just before your air separator, depending on the type and size you are using. The difference in cost between a 2" and 1.5" or 1.25" air separator can be large. I have a preference for the Taco 4900 series separators using PALL rings. Nice castings, well-made.



From there, your distribution will dictate- you may have a header with multiple circulators, a main circulator with zone valves, what have you.



My $0.02 anyway.

John B_2

Would you use iron pipe or copper 2 inch?

I looked up Taco 4900 2 inch, what are pal rings?

John B_2

disregard the pall ring question...looked it up.

still copper or iron?

Brad White

I would use

iron coming out of the boiler, including the elbow to horizontal, then the brass air separator and copper thereafter.



Alternate Approach:

If you are supporting several circulators and such off the piping after the air separator,  exit the air separator with iron. (An EarthLee header is a treat.) Iron is better able to support weight, not that copper is flimsy, but iron is so much more substantial.



Make the transition to copper either at the circulator outlet or, if you are using zone valves, via a brass ball valve. That is our standard for dissimilar metal separation.

lolo21

curious about 260kbtus output on 1-1/4" new boilers

I saw your answer and I am curious about the new mod-cons having an output of 250-280kbtus through a 1-1/4" tap and installing them in buildings with much larger pipes= 1-1/2" to 4".



I beleive the maximum flow is going to be determined by the 1-1/4" boiler tap.... right?

thanks

Brad White

Not necessarily

Most modcons have a higher internal velocity and pressure drop, whereas the older cast iron boilers, some of those patterns date from one hundred years ago and were based on steam or gravity HW designs,  low velocities and low pressure drops.  The manufacturers might have given a bit of updating but nothing extreme. Rather than update the patterns or machining, giving a large tap preserves the installers options and they can always bush down.



With the modcons, once you are out of the boiler, you can expand (or reduce) to suit your system side flow rates.