HW Boiler > Supply Header > Circ Pumps - Where to Reduce Pipe Size?

Reply

  #1  
Old 02-23-14, 07:19 PM
Member
Thread Starter
Join Date: Jan 2014
Location: United States
Posts: 41
Received 0 Votes on 0 Posts
Question HW Boiler > Supply Header > Circ Pumps - Where to Reduce Pipe Size?

I am planning a hot water oil-fired boiler replacement, 2 zones w/circ pumps + an indirect. I am moving circ pumps from return to supply side. So the near boiler supply piping is 1-1/4" NPT but should that be reduced somewhere before it gets to the circ pumps off the supply header? Or is it 1-1/4" including the supply header and off that going to each Circ pump, is that where I reduce it down to 1" or 3/4" at the input of the Circ pumps? Of course the output of the circ pumps will be 3/4".

In looking at the old installation it appears it was 1-1/4" to the input of the air separator and reduced 1" on the output, and then each zone off that was reduced to 3/4".

thanks for all the input
 
Sponsored Links
  #2  
Old 02-23-14, 07:36 PM
Member
Thread Starter
Join Date: Jan 2014
Location: United States
Posts: 41
Received 0 Votes on 0 Posts
In looking at some installation pics it looks like I can reduce down to 1" after the near boiler piping, and before the air separator. Supply manifold would be 1" with 3/4" pipes going up to the circ pump input.
 
  #3  
Old 02-23-14, 07:47 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 2 Votes on 2 Posts
A general rule that most installers follow is that when feeding a pair of certain pipe size, the feed pipe should be one size larger.

So, two 1/2 into 3/4

two 3/4 into 1
four 1/2 into 1

two 1 into 1-1/4
four 3/4 into 1-1/4
eight 1/2 into 1-1/4

So you are fine feeding two 3/4" loops from a 1" manifold. Are you sure you're never going to expand? You'll never, ever, need another 3/4" feed, say for an indirect?

There's nothing at all 'wrong' with feeding a pair of 3/4 from 1-1/4 and adding a couple of 'stubs' to the manifold for future expansion!

Some guys figure that if there are 4 zones, the chances that they will all call at the same time are sorta slim, and will go with 1" feeding four 3/4", just to save a couple bucks on the copper, but for 1-1/4 you will probably be using steel anyway... so why not do it 'right'?

SOME overkill is not a bad thing!

This assures that flow velocity in the pipes remains around 4 feet per second, which is considered about optimum.

Above this size, things change a bit...
 
  #4  
Old 02-23-14, 07:53 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 2 Votes on 2 Posts
I just noticed you're doing an indirect in addition to the 2 zones.

You really should pipe the indirect in ONE INCH if you wanna do it right.

I would probably do this with 1-1/4 black, take a 1" off for the indirect as the first tap on the manifold after the boiler, then the two 3/4" zones after that.
 
  #5  
Old 02-23-14, 07:55 PM
Member
Thread Starter
Join Date: Jan 2014
Location: United States
Posts: 41
Received 0 Votes on 0 Posts
This is the kind of info I need Trooper... thank you. I will be feeding 3 circ pumps (2 heating zones plus indirect HW tank) off the manifold plus I will add one stub for future expansion. By the guidance given it seems I should have a 1-1/4" supply header and the pipe going to each circ will be be 3/4."
 
  #6  
Old 02-23-14, 08:04 PM
Member
Thread Starter
Join Date: Jan 2014
Location: United States
Posts: 41
Received 0 Votes on 0 Posts
Indirect HW Pipe Size

You are saying pipe my whole indirect supply and return paths with 1" vice 3/4"? I was trying not to touch the indirect piping with the boiler change.
 
  #7  
Old 02-24-14, 11:12 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 2 Votes on 2 Posts
You are saying pipe my whole indirect supply and return paths with 1" vice 3/4"? I was trying not to touch the indirect piping with the boiler change
That's 'optimal'. MANY indirects are piped with 3/4" and work fine, and apparently yours has been that way for a long time as well... I guess it's really about 'not fixing it if it ain't broke' and economics. I wouldn't fault you if you chose to keep the existing piping...
 
  #8  
Old 02-24-14, 12:08 PM
Member
Thread Starter
Join Date: Jan 2014
Location: United States
Posts: 41
Received 0 Votes on 0 Posts
I will keep this in mind though... and re-plumb if necessary, thanks!
 
  #9  
Old 02-24-14, 07:13 PM
rbeck's Avatar
Member
Join Date: Jul 2007
Location: Pennsylvania
Posts: 2,449
Received 1 Vote on 1 Post
Keep in mind by using the smaller 3/4" pipe will move less water and the boiler will short cycle more which affects efficiency.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: