Hi all...

I'm running just 20 feet of sched 40 black pipe from propane tanks (40 lb), and with the pipe sizing charts, I'm in good shape...

The system is 11" w.c. undiluted propane... use is 140K BTU. 20' of black pipe can handle 200K.

However... I'm finding it easier to switch to soft copper (type L) for a final 4 feet. And I wanted to get 1/2" but grabbed 3/8" because it was the only tubing they had in stock at the time. I figured "it's close"... but when I checked the charts, 3/8" has a MUCH lower capacity than 1/2".

I'm unsure how to calculate what is happening with the change... since I'm only running copper for the last 4 feet... it's not clear to me how to calculate the total system.

Diagram:

Propane regulator ----- 20' 1/2" black pipe---->adapter----> 4 feet 3/8" copper--->140,000 BTU usage.


Note: The minimum inlet pressure at the appliance is 8" w.c.


Can I figure this system using the tables in some manner? Or maybe I'll need some fancier calculations?

Thanks for your kind help!

R



Edited 1 times.

can't you run another couple of feet of black pipe and use a flexible appliance connector for the last couple?

Which 3/8" copper do you have? 3/8" I.D. copper is fairly rare, 3/8" O.D. is very common. IF it is the larger one, you should be good.

Howdy...

Yes... I could "snake" some black pipe through... but I'd have about 6 fittings and lots of custom lengths to get through this last tricky part... where just bending flex through is easy, and of course less likely to ever leak. The other reason is that the tricky part is also going to be inaccessible... and even though this doesn't have to meet code or anything, threaded fittings in such areas are not allowable by code for a reason.


And yes, it's 1/2" O.D. , 3/8 nominal flex line...

The problem is the branch length method for sizing requires that you size for the entire length of the run... and of course 3/8" over 24'feet obviously won't fly.

I did the layout on some software (PCAD) that said it would work fine... but it's only for natural gas, so I couldn't use the final numbers... and natural gas performs a lot better than propane in the smaller diameter copper. (why PCAD doesn't have a propane option is beyond me... it would be the easiest thing to add).

I'm thinking I should just go out and get the half inch flex copper from someone who has it in stock... call it done.

The sad part is that I already installed it, and will have to tear out the 3/8".

Live and learn I guess.



Just in case anyone knows: Does anyone here have experience using the low pressure formula for manually sizing pipe? I tried doing it this way as well, but the results weren't right... calling for even larger pipe than the tables do, which absolutely should not be the case. If anything, the tables should be more conservative than the formula.

I'm calculating 20 feet of propane, 11" wc in, drop of 0.5" wc, and I'm getting a pipe size of .76" for only 140K BTUs!

That's BS if you go by the tables... which say that 3/4" pipe can carry 418K BTUs. So something's not right.


Thanks!

R



Edited 1 times.

quote; threaded fittings in such areas are not allowable by code for a reason.

Since when? If you can rotate the fittings with a wrench you CAN install it. Many, if not most, fittings are "inaccessible" once the job is done.

I'd love to chat about that... but I'd rather stick to the matter at hand... thanks!

R

It will be fine the way you have it.

Hi Paul... well, that's at least sounding reassuring... but I'm a numbers kind of guy. Might you share why It will be ok, given the performance of 3/8"? Obviously the 3/8" run is short, and that makes a huge difference, but I'd love to calculate it.

[lp-gasequipment.com] You have to extrapolate for the 1/2"OD copper tube. If in doubt add a short section of larger OD close to where you are terminating.