What is the RIGHT size of copper tubing for LPG?

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What is the RIGHT size of copper tubing for LPG?

Postby OP827 » Thu Nov 24, 2016 9:12 pm

The reason for this post is that I want to "design for purpose" my build propane system. I feel that running a 1/2" black iron pipe maybe a little bit too heavy and also could be more expensive that cooper tubing that I understand is OK to use for travel trailers, but what size is right?
Since I could not quite find such information on this board here, i.e. what diameter of tubing has to be used in the propane trailer system, I thought I'd start a thread to specifically discuss minimal required tubing size. I have to mention, that I am doing that at my own risk, I have no certifications in this field, so use it at your own risk and discretion.

If you find any errors in my discussion below, I'd appreciate if you please let me and everybody know.

Now, I thought that the tubing size would be driven by a total capacity of appliances I have in BTU, so let's start to summit it up:

1. Hydro Flame BRC-10A Furnace - requires input of up to 10,000BTU. I will assume 12,000btu, in case I will change it to forced air atwood compact furnace in the future.

2. Two Burner cooktop, Flame King - 7,200+5,200=12400BTU

3. Dometic RM211 Fridge (http://www.nationalserroscotty.org/resources/DometicRM211.pdf). I could not readily find online what is required BTU input for this unit, so I am going to safely assume 5000BTU, I am sure the real number is lower than that, just by seeing how small amount of heat is produced by similar units in real circumstances.

Next, since we all usually "overbuild" here, I will assume that all appliances may run at a full capacity, because it can theoretically happen:
12,000+12,400+5,000=29400BTU

Then with 29400BTU total requirement in mind, I've searched and found this table online (http://inspectapedia.com/plumbing/LP_Gas_Line_Sizing_LPGE_Co.pdf).
That table shows what is the maximum BTU capacity for every particular tubing size is required with 11"WC LPG pressure with 1/2" pressure drop. I should probably assume that such 1/2" pressure drop would be OK for most appliances and also the fact that pressure regulator can be adjusted slightly to increase this pressure at regulator output.

One more parameter is at play here, which is the length of tubing from my LPG bottle regulator to the appliances. I estimate my length will be at maximum of 15 feet.
So, as per first page, first table, first row - 3/8" tubing of 20 feet length will work for maximum of 34,000BTU.

Conclusion: I can run 3/8" tubing and use all three appliances at the same time.

Again let me know if I can be missing anything.

Thanks,

Oleg
My foldable foam trailer build: http://www.tnttt.com/viewtopic.php?f=50&t=61344
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Re: What is the RIGHT size of copper tubing for LPG?

Postby OP827 » Thu Nov 24, 2016 10:18 pm

Found the btu rating for my size Dometic refrigerator and it is much less than 5000btu, it only requires 635BTU at high according to this spare parts list - http://www2.dometic.com/d5cc849a-fb08-49a0-a703-d488f773cf9e.fodoc

That brings down my all three appliances total propane need roughly to 25,000BTU. With some room to spare the 3/8" diam x 15 feet long tubing should do the work.
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Re: What is the RIGHT size of copper tubing for LPG?

Postby Shadow Catcher » Thu Nov 24, 2016 10:52 pm

I used 3/8 and have not had a problem. BUT I also have a two stage regulator. Three burner cook top, 6 gallon water heater and a gas grill so I potentially am using more Btu than you will.
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Re: What is the RIGHT size of copper tubing for LPG?

Postby John61CT » Thu Nov 24, 2016 10:56 pm

My seat of the pants for RV context is 1/4 for shorter runs to single appliances from a manifold/T-split, 3/8 for long runs to get close to the highest-use one before splitting. Gives room if you want to tap a T in later. Note not qualified here, would appreciate being corrected.
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Re: What is the RIGHT size of copper tubing for LPG?

Postby OP827 » Thu Nov 24, 2016 11:16 pm

Shadow Catcher wrote:I used 3/8 and have not had a problem. BUT I also have a two stage regulator. Three burner cook top, 6 gallon water heater and a gas grill so I potentially am using more Btu than you will.


Did you buy your 3/8 tubing from specialty supplier or HD or other hardware store? I now wonder what is the difference between "General purpose" from HD and "type k" 3/8 tubing for a specialty supplier except price, they both have same .035" wall thickness.. some alloy properties maybe?
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Re: What is the RIGHT size of copper tubing for LPG?

Postby OP827 » Thu Nov 24, 2016 11:22 pm

Shadow Catcher wrote:.. BUT I also have a two stage regulator. Three burner cook top, 6 gallon water heater and a gas grill so I potentially am using more Btu than you will.


The single stage regulator that I am using came from a tent trailer donor that had the same size fridge as mine, 3 burner cooktop and bigger forced air heater. So I wonder if two stage regulator is also a neccessity for 3 small(ish) appliance set?
The tent trailer also used 3/8 tubing everywhere except flex houses to appliances due to fold able kitchen design..
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Re: What is the RIGHT size of copper tubing for LPG?

Postby Shadow Catcher » Fri Nov 25, 2016 4:27 pm

Here is the justification for a single vs two stage regulator.
Single stage and two stage gas regulators have different droop characteristics (Droop is the difference in delivery pressure between zero flow conditions and the gas regulator's maximum flow capacity) and respond differently to changing supply pressure. The single stage regulator shows little droop with varying flow rates, but a relatively large supply pressure effect. Conversely, the two stage regulator shows a steeper slope in droop but only small supply pressure effects.
Two stage is I understand required for RV's.
Since I have a couple of high flow usages, water heater and grill and wanted not much fluctuation I went with two stage.
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Re: What is the RIGHT size of copper tubing for LPG?

Postby John61CT » Fri Nov 25, 2016 7:53 pm

In my wannabee technical discussion with the Manchester regional manager, he was emphatic in stating I should do two-stage, my impression was for safety reasons, may be better at handling possible liquid flow?
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Re: What is the RIGHT size of copper tubing for LPG?

Postby OP827 » Fri Nov 25, 2016 11:52 pm

Shadow Catcher wrote:Here is the justification for a single vs two stage regulator.
Single stage and two stage gas regulators have different droop characteristics (Droop is the difference in delivery pressure between zero flow conditions and the gas regulator's maximum flow capacity) and respond differently to changing supply pressure. The single stage regulator shows little droop with varying flow rates, but a relatively large supply pressure effect. Conversely, the two stage regulator shows a steeper slope in droop but only small supply pressure effects.
Two stage is I understand required for RV's.
Since I have a couple of high flow usages, water heater and grill and wanted not much fluctuation I went with two stage.


SC, where are you getting your 3/8 copper tubing, fittings and valves?
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Re: What is the RIGHT size of copper tubing for LPG?

Postby Shadow Catcher » Sun Nov 27, 2016 8:33 am

From a local plumbing supply. These are flare fittings and I do a leak check, (so far have not had any) all of the fittings are below the tear where I can get to them and where if there is a leak (Propane is heavier than air) it will disperse.
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Re: What is the RIGHT size of copper tubing for LPG?

Postby OP827 » Sun Nov 27, 2016 1:02 pm

Thanks SC, my plan is similar, all fittings will be located either outside or under the lower fridge vent that is of course vented to outside. All appliances are going to be connected with copper flare connections matching appliances. No hoses inside the trailer. The only hose planned is from LPG bottle to regulator. I found two gas/propane specialty vendors in my area, will talk to them this coming week.
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Re: What is the RIGHT size of copper tubing for LPG?

Postby John61CT » Sun Nov 27, 2016 7:52 pm

Isn't it the case that pipe/NPT fittings with dope or yellow tape are better than flare connections? I've read that flares can crack where the copper's been deformed?
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Re: What is the RIGHT size of copper tubing for LPG?

Postby OP827 » Mon Nov 28, 2016 2:01 am

John61CT wrote:Isn't it the case that pipe/NPT fittings with dope or yellow tape are better than flare connections? I've read that flares can crack where the copper's been deformed?

Don't know, do you mean black iron pipe? I do not like it due to heavy weight. As for cracking, please share where your found this information. Flare connections are recommended for RV and vibration application as I read it.
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Re: What is the RIGHT size of copper tubing for LPG?

Postby John61CT » Mon Nov 28, 2016 2:45 am

No, brass fittings, junctions, adapters, cylinders & regulators, I believe are usually NPT thread specs, require yellow tape or "dope" sealant for propane.

http://www.homebrewtalk.com/gallery/dat ... RearMT.jpg

the flare type (or brazing) is used for the tubing side

Couldn't find where I read the cracking flares issue, probably just someone's opinion, but don't overtighten in any case.
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