Correctly Sizing Propane Lines for the Entire Coach? (Isata 5, 35DB)

[BLT4SPD]

Okay, looking for a little bit of guidance on propane plumbing. I completely understand the fundamentals and the various components needed to make everything work. However, when I struggling a little bit is on sizing the plumbing. Here’s the scenario:

I am making significant changes on our Isata 5 in terms of how the propane is plumbed and where the hoses are routed. Based on my shopping experience for parts for this project I THOUGHT that pretty much anything before the regulator (high pressure side) would be 1/4" hose and anything after the regulator (low pressure side) would be 3/8” hose. However, now that I am crawling around under our coach, I see that Dynamax installed 1/2" hose on the low pressure side for the trunk line and branch connections are 3/8”.

Now for the questions: How important is it that the trunk is 1/2"? ……and I ask because 3/8” propane hoses are REALLY easy to find, but 1/2" hoses seem less common. I have no doubt that there is some sort of rule of thumb for sizing the main trunk line based on all the various things that are connected to it, but what is it? Would I be shooting myself in the foot by changing the trunk line to 3/8”?

[CHICKDOE]

just off hand i would say you would be ok if you only had one device running at a time. as it is each device is constrained by the 3/8 hose that connects it to the main.

but if you tried to run two devices at the same time the now reduced 3/8 main might not support a to both devices.

i do not know this as a fact. but in most plumbing it is common to have a larger main than the branches just for this reason.

[BLT4SPD]

Originally Posted by CHICKDOE

just off hand i would say you would be ok if you only had one device running at a time. as it is each device is constrained by the 3/8 hose that connects it to the main.

but if you tried to run two devices at the same time the now reduced 3/8 main might not support a to both devices.

i do not know this as a fact. but in most plumbing it is common to have a larger main than the branches just for this reason.

Agree that in most cases, a main line will be larger than a branch line. However, if I put this in another context like the domestic water plumbing in our coaches, it’s 1/2" across the board. From the point of connection to every fixture in the coach, it’s 1/2". Now if I turn a faucet on, it’s fine. If I turn a second faucet it, it’ll almost certainly be fine as well. Of course, the more I turn on, I’m going to start noticing a pressure loss at each device. I assume propane works the same way, BUT at what point would I start noticing a problem?

[nomad297]

Gas line sizing is based on the total BTUs of the system and the longest run. It is sized such that there is no more than a 1/2” water column drop when any appliance is being used. It takes into consideration that all appliances on the system may be using gas at the same time. More than a 1/2” water column drop could cause an appliance to not function properly and it could also rob the gas from a pilot or a low-consumption appliance enough to snuff it out. If the gas system was designed with a 1/2” trunk, there is a reason.

Bruce

[BLT4SPD]

Originally Posted by nomad297

Gas line sizing is based on the total BTUs of the system and the longest run. It is sized such that there is no more than a 1/2” water column drop when any appliance is being used. It takes into consideration that all appliances on the system may be using gas at the same time. More than a 1/2” water column drop could cause an appliance to not function properly and it could also rob the gas from a pilot or a low-consumption appliance enough to snuff it out. If the gas system was designed with a 1/2” trunk, there is a reason.

Bruce

Fair enough and I’d like to keep it at a 1/2" trunk, but it is interesting to see just how hard it is to track down 1/2" propane hoses.

Okay, new sizing question……My current set up has the 2-stage regulator connected directly to the hard mounted (chassis) tank via a 1/4npt to soft-nosed POL fitting. I would like to divorce the regulator from the tank and remote mount it as part of this project. Since I currently don’t have ANY hose in-between the tank and regulator, I don’t have anything to compare to. It appears that MOST all other RVs running around out there that have a soft line in-between the tank and regulator are using 1/4". Any scientific way to size the high pressure supply side?

[nomad297]

Originally Posted by BLT4SPD

Fair enough and I’d like to keep it at a 1/2" trunk, but it is interesting to see just how hard it is to track down 1/2" propane hoses.

Okay, new sizing question……My current set up has the 2-stage regulator connected directly to the hard mounted (chassis) tank via a 1/4npt to soft-nosed POL fitting. I would like to divorce the regulator from the tank and remote mount it as part of this project. Since I currently don’t have ANY hose in-between the tank and regulator, I don’t have anything to compare to. It appears that MOST all other RVs running around out there that have a soft line in-between the tank and regulator are using 1/4". Any scientific way to size the high pressure supply side?

This is beyond my realm of knowledge. You might benefit from driving your rig up to a local propane distributor and asking there.

Bruce

[Iwannacamp]

It's prolly here.....

http://www.squibbtaylor.com/uploaded...icemaninst.pdf

[Iwannacamp]

this might help too..

https://rvshare.com/blog/rv-propane-regulator/

[tonys]

propane at home uses copper tubing for transmission, maybe this is an option for you, 1/2" copper is easily found.

[CHICKDOE]

actually, both our house propane lines and the trailer main line use black iron pipe. it is readily available and any hardware store.

[bubbles]

If wanting to reduce from 1/2 inch because it is hard to find and 1/2 inch is minimum requirement why not just go up in size.