Author Topic: Pipe Sizing  (Read 837 times)

Offline walker

  • Pro Tech™
  • *****
  • Posts: 463
Pipe Sizing
« on: April 29, 2017, 11:14:19 AM »
Just a quick question about pipe sizing for residential

Typically we would use the sizing chart from 7-14"w.c. ?

I'm seeing a lot of pressure test tags where the fitter just put system pressure as 7"w.c.

I know I'm mostly measuring pressures around 7-10"w.c. on the supply side of things.

I'm just trying to figure out the size I need on a long run for a Tankless it's about 30ft from the main supply and the LMR is 50'.  Trying to be able to stick with 3/4" black or 7/8" copper.

Total BTU is 260,000.

Offline Porcupinepuffer

  • Pro Tech™
  • *****
  • Posts: 398
Re: Pipe Sizing
« Reply #1 on: April 29, 2017, 02:00:27 PM »
 I go with table A.2 or A.9. Is the main supply 1" black iron? It seems with you would need to go to the next size up. I wouldn't even consider copper at the size required. Sometimes we do it with wardflex or tracpipe if there's enough twists and turns that back iron may take too long, or be too difficult.
The majority of piping is undersized when you go by the methods we're supposed to use. Most techs are never sizing their branches from the meter.

Offline walker

  • Pro Tech™
  • *****
  • Posts: 463
Re: Pipe Sizing
« Reply #2 on: April 29, 2017, 02:04:31 PM »
Yeah it's 1" coming in to the home for about 10ft, the it's reduced to 3/4 for about 5' then branches off 1/2" to furnace, and then hopefully I can use 3/4" black from the main 1"

Offline Admin

  • Administrator
  • *****
  • Posts: 2052
    • HVAC TECH GROUP
Re: Pipe Sizing
« Reply #3 on: April 29, 2017, 03:25:29 PM »
There's no requirement to write the system pressure on a pressure test tag.  Only the test pressure and duration.  E.G. 15 psi @ 15min.

Follow Table A.2,

3/4" @ 50' = 199,000 BTU

1" @ 50' = 374,000 BTU

It looks like you need to run 1" to the pool heater.

Offline walker

  • Pro Tech™
  • *****
  • Posts: 463
Re: Pipe Sizing
« Reply #4 on: April 29, 2017, 03:31:32 PM »
Pool heater, you mean Tankless.  So I'll just tee off on the ansment and run a 1" to it.  How far away from the Tankless can I step down to a 3/4" for my shut off?

Offline Porcupinepuffer

  • Pro Tech™
  • *****
  • Posts: 398
Re: Pipe Sizing
« Reply #5 on: April 29, 2017, 04:27:22 PM »
I'd drop off from ceiling height to 3/4" going down to it. I can't say I've ever seen a 1" drop coming down to a tankless before. That short a length won't give you any pressure drop issues.

Offline walker

  • Pro Tech™
  • *****
  • Posts: 463
Re: Pipe Sizing
« Reply #6 on: April 29, 2017, 04:28:49 PM »
Alright thanks!

Offline Admin

  • Administrator
  • *****
  • Posts: 2052
    • HVAC TECH GROUP
Re: Pipe Sizing
« Reply #7 on: May 06, 2017, 03:59:52 PM »
Tankless sorry!  260,000 BTU's is a big water heater.  It likely has a 3/4" gas valve outlet though, so a 3/4" drop would be fine.  I've always played it safe and ran 1" as far as possible, until the drop.  I wouldn't be suprised if 3/4" the whole 30' would work.  Just verify the pressure drop is under 1" w.c. with everything running.

Offline walker

  • Pro Tech™
  • *****
  • Posts: 463
Re: Pipe Sizing
« Reply #8 on: May 06, 2017, 04:02:41 PM »
I just ran 1" black the entire way until the drop.

How do I check the pressure drop?

Offline Admin

  • Administrator
  • *****
  • Posts: 2052
    • HVAC TECH GROUP
Re: Pipe Sizing
« Reply #9 on: May 06, 2017, 04:48:28 PM »
Turn all the gas appliances off and, at the farthest appliance, measure the inlet pressure on the gas valve.  E.G. 7" w.c.

Then start all the gas appliances and re-check the gas pressure at the same spot.  In our example anything higher than 6" w.c. is okay.

I would also re-test at the newly installed appliance.

Offline walker

  • Pro Tech™
  • *****
  • Posts: 463
Re: Pipe Sizing
« Reply #10 on: May 06, 2017, 04:50:13 PM »
Okay that's what I thought.  I usually check at the appliance I'm installing the inlet pressure with and without it running.