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Old 09-16-2011, 11:26 AM   #15
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Originally Posted by Aage View Post
I'm wondering if we can all agree on what the size should be?

Does this sound right?

5/8" OD main line (including off the tanks?) and 3/8" OD after the regulator, going to each appliance

Or do we need to use ID measurements, and if so, what would they be?

Thanks. I am replacing my furnace this year, and did my water heater last year, and I want to make sure that I put the proper size in.

I know this is an old thread, but I am doing some research on LP since I am building a new system, and I just wanted to point out that unless anyone is buying specialty propane regulators, the ones I have seen (esp. the one on VTS that I bought) has an outlet fitting size of just shy of 7/16".

So there is zero reason to go any larger than 1/2" ID or 5/8" OD for the main pipe because you are going through a smaller orifice to get there regardless.--Just in case someone was thinking of going to a larger size to be "safer", it's not necessary.

Yet I still haven't answered the questions I looked through these threads for....

- Peter (and Marie)

1959 Pacer 18' Renovation - Knight in Shining Armor

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Old 07-07-2015, 08:42 PM   #16
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Resurrecting an old thread just because ...

The size of copper ID or OD, soft (bendable) and rigid sticks, types M, L etc. explained here:

The size of the gas line used is based on the number of BTUs used at each fixture/appliance.

So for example my 10,000 BTU water heater using type L soft copper is perfectly happy with 1/4" ID, 3/8" OD for a pipe run as long as about 80 feet. Propane Gas - Pipe Sizing

If I add up all of my propane requirements of hot water heater, fridge, furnace and range top I get roughly 60,000 BTU which is more than covered using 1/2" black pipe or 3/8" ID, 1/2" OD type L soft as my main distribution line from tanks under the belly to the entry point up into the trailer.

The two stage regulator near the tanks drops the tank pressure (~200 psi) to 10 psi then 11 inches water column.

Testing a new system or one that has been opened for repair is done first with compressed air - some claim ~3 psi for 10 minutes (11 inches water column is roughly 0.5 psi). Once there are no obvious leaks, the normal annual checks can be made.

Or I could be confused ....

Signed, a retired stationary engineer turned rv mechanic wannabe

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Old 07-07-2015, 08:54 PM   #17
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Originally Posted by nrgtrakr View Post
more than covered using 1/2" black
Thanks for resurrecting!

Above, I think you refer to the ID of the black pipe being 1/2"?

I need to run black pipe underneath my Streamline.

I suppose there's no harm in running 1/2" black pipe for the branches, too, other than weight?

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Old 07-07-2015, 09:27 PM   #18
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Anytime ...

Mostly my posts are a result of me reviewing things before actually doing them.

Technically 1/2" steel pipe is 0.84" OD and 0.62" ID.

I've read a lot of comments claiming one type of pipe preferred over another. I even attempted to access the RVIA current standards but had the wrong decoder ring.

In practice both are used - all soft copper, or black to point of entry then soft copper.

The underside of my 75 Overlander looks like the cat was playing with it, or someone was using an etch-a-sketch.

I prefer the orderliness of radars, missile launchers, airplanes, etc. Plus the beautification engineer suggested a gas do over after seeing the plumbing job.

So I'll likely run standard Acme nut pig tails to an auto change over dual stage regulator to 3/8" propane hose to 1/2" black from the tongue tank mounts directly rearward to a T then a 1/2" branch to either side of the belly to within stricking distance of the furnace and range curb side, and fridge and water heater street side - each black pipe stub fitted with a flare end ball shut off valve and lots of support clamps for the rigid run.

The nay sayers will claim the trailer flexes too much for rigid pipe. If this proves true, I can always replace the rigid with soft. But then a lot of manufacturers would be swaping rigid for soft also.

The appliances in a home have a flex gas line, similarly and because those residential flex lines aren't suitable for an RV, an RV uses soft copper with flaired fittings to hook up to the appliances.

Hopefully a real RV tech certified for gas will correct any misconceptions in any or all of this. My simple training and experience as a stationary engineer sees nothing scary so far.

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