Natural gas pipe size question

I am remodeling two of the apartments in a 3-unit apartment building that I own. It's a 3-floor building with one apartment on each floor. All of the utilities are separate, so each apartment pays all of their own utilities including heat, hot water, cooking gas, and electric.
The bottom floor also has a separate room for the 3 gas heaters/boilers for each unit's hot water baseboard heat, and the 3 gas hot water heaters. There are also 3 gas meters down there-- one for each apartment.
What I want to do is move and replace the gas lines that now go to the 3 heaters/boilers, 3 hot water heaters, and the 3 gas cooking stoves/ovens. As far as I can tell, most of the existing gas supply lines that I will be replacing are way bigger than they need to be, so I am trying to figure out if I can replace them with smaller size black iron pipe.
My basic question is: "What size black iron gas pipes do I need for the replacement pipes?"
Here are some additional details:
1) The main gas supply line coming into the building looks like it is about 1-1/2 inch black iron pipe. It's possible that it is 2 inches (I forgot to measure it before posting this).
2) The main gas supply line has 3 gas meters coming off of it -- one for each apartment.
3) Looking at the fittings that come out of the gas meter for each unit, it looks to me like there is a reducer fitting on each one with the smallest end of the reducer fitting being 1/2-inch, I think (but possibly 3/4-inch at most -- I'll double check).
4) All 3 units have black iron pipe gas supply lines AFTER the meter that are about 1-1/2 inch each.
5) Each unit's 1-1/2 inch gas supply line then splits off and supplies: one 100,000 BTU gas heater/boiler, one 30-gallon gas hot water heater, and one 24-inch apartment size gas cooking stove and oven.
I know that with water lines, once the main line is reduced down to a size of say 1/2-inch, making any lines past that reduction point larger than 1/2-inch is pointless because the maximum flow has already been reduced the 1/2-inch. Do natural gas lines work the same way? In other words, if the pipe line coming out of the gas meter goes through a reducer fitting that is no larger than 1/2-inch, does that mean that any pipes after that point do not need to be any larger that 1/2-inch?
I'm using the "logic" that there is no point and no need to replace the existing lines with pipe that is any larger than the size to which the gas line coming out of each meter has been reduced. Is that correct?
Or, to look at it another way, if a natural gas line is split to supply 3 things -- a 100,000 BTU gas heater/boiler, and 30-gallon gas hot water heater, and a 24-inch apartment size gas cooking stove and oven -- what size does it need to be? Will 1/2-inch black iron pipe or 3/4-inch black iron pipe be sufficient throughout that system for each unit?
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Len56 wrote:

3/4" from the meter to the boiler, then 1/2" after that will be big enough for the devices you've mentioned.
s
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There are a couple of web sites that have gas piping information. You seem to have most of what you need to do the calculations. You already stated you forgot to measure the incoming line, you are not sure of the reducer size, yet you want us to give you accurate information.

Your logic is about right. You must also factor in distance, and elbows. Find the chart, do the calculations and you will be OK.
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Ed Pawlowski wrote:

First, I don't know why you can't just read my mind and tell me what the answer is without making me do a bunch of calculations! :-)
But, seriously, thanks. I didn't know about the calculation charts and just did a search and found some. Here are a few examples:
http://www.engineeringtoolbox.com/natural-gas-pipe-sizing-d_826.html
http://www.ci.newark.ca.us/externals/9a/067599d8f4eeb035e24a389046319224aef4dd.pdf
http://hvactechnicaltraining.com/files/Natural_Gas_Pipe_Sizing.ppt
That last one is freakin' amazing. It's a power point presentation that goes through the process step by step. I'll go back to the property and do the measurements and then do the calculations using the power point presentation as a guide.
I'll check again on the pipe sizes that are already there -- including what the size is of the reducer fitting coming out of each meter. I have a hunch that natural gas piping may be different than water piping since I know that the reducer fitting at each meter is definitely a lot smaller than the main pipe that each one connects to. In fact, the "reducer" is more like an "expander" because each one coming out of each gas meter starts out small and then converts that size to a larger fitting. So, maybe gas lines are more dpendent on the length of the pipe as a factor than any one point (such as at the meter) where the size may be smaller.
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Have you checked with your local code people? There might be some silly rules about this.
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You need gas flow when its the coldest day, pressure is lower and everything is on, a Manometer will measure gas flow.
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ransley wrote:

My manometers only measure gas pressure. Where can I get one that will measure gas flow? Perhaps if I used a flow meter I could measure gas flow but those damn things are so expensive.
TDD
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No matter what you learn from your inquires it would be irresponsible of you to undertake this project without the help of a licensed gas fitter. If the local or state government does not provide inspection services then the gas supplier will. If you do this project without the benefit of permit and inspection and it causes any harm to anyone you will be solely responsible for the harm. If inspection after a fire were to reveal that there was uninspected gas fitting involved as the source of the "fuel first ignited" or as a contributing factor in the spread of the fire your insurance carrier could walk away from the loss. Everybody may reassure you that never happens but since I was a defense witness for the insurance company in such a case I know that is not true. When the trial was over the court ruled that it was a legal absurdity to insure against the consequences of your own unlawful act and directed a decision for the insurer. The judge told the plaintiffs who were trying to force the insurer to pay the loss that their only hope of prevailing had always been to prove that the loss was not caused by an unlawful act on the part of the insured. Having failed to even argue that was the fact the judge would not let the case go to the jury and directed a finding for the insurance carrier. The unlawful act in that case was electrical work without permit or inspection resulting in a fire of electrical origin from the bootleg wiring. If your work were to cause a death you would almost certainly be charged with manslaughter or your states equivalent. Remember that the so called Fireman's rule that prevents a firefighter from suing you for causing him harm does not prevent a prosecutor from seeking an indictment against you in criminal court if a responder were killed fighting a fire in that building. Remember also that there is no rule to prevent your tenants from suing you for the harm you cause them. Unless you have left out a lot of information it sounds like your driving around a neighborhood full of drunks with your head out your car window after having given out a great many machetes. My interest is that I am one of the guys and gals that crawl down long snotty hallways at 0dark30 looking for other peoples relatives. I'm suggesting that you consider that the money you might save is not worth the risk.
-- Tom Horne
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Tom Horne wrote:

I see that crap all the time. The last inspection I had, the inspector took a look at the work and because of his experience with inspecting my jobs, said he didn't need to come back for a final. You get a reputation for doing it right and inspections go a lot easier. I won't just throw the equipment in, I take the time to do it correctly the first time so I don't have to do it over. I wish more folks out there would take pride in their work. It actually saves money.
TDD
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I think that everything you wrote is completely correct. And it seems like you've "been there, done that, and bought the T-shirt" (at least as a defense witness) in what sounds like was an interesting directed verdict insurance case. As it turns out, I am one of those guys and gals that treat the people (including firefighters) who get dragged out of those structure fires at 0dark30 hours.
Although I wrote this as if I were definitely going to do the work myself, I am not sure I would actually want to do that -- especially for natural gas lines. For one thing, I could easily picture myself being in the middle of working and something going wrong and a gas leak developing, and then having to call the fire department and the gas company, who of course would want to know what the heck I was doing and where was my permit, etc. But, I'm in the deciding/planning stage right now, so I am trying to learn more about how this stuff works and what makes sense and what doesn't. Then I could decide on what I want done (if anything) and who it would be best to use to get the work done. Nevertheless, I wrote it with a lot "I" am about to do this, and "I" want to do that, etc. because it's just easier to write it that way.
I've already learned a lot of good stuff here on this topic. For one thing, I see now why the existing gas lines seem to be so big. From the calculation charts that people suggested I check out, it looks like the current sizes are within reason -- mostly because there are a lot of fairly long runs from the gas meters to the heaters etc.
In response to another message in this thread I'll explain a little more about what I am considering doing (having done) and why.
Tom Horne wrote:

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As you have learned, there are useful charts & calculators for gas line layout calcs.
Your comment....

gas line coming out of each meter has been reduced. Is that correct? <<<<<<
is not quite correct....fluid flow (gas or liquid), volume & pressure drop are determined by not only the size of the piping but also the lengths of each pipe size & the piping layout (& of course, the type of pipe).
A residential service might have a 3/4" fitting just downstream of the gas meter but then the piping bumps back up to 1" pipe that serves as a "main" for the house. This mainline branched off of to supply the furnace, water heater, stove, oven, pool heater, air conditioner, etc.
Fifty feet of 1" pipe following of a few inches of 3/4" pipe / fittings has a different BTU capacity than 50' of 3/4" pipe.
As an extreme example......what arrangement would have lower total pressure loss & be able to deliver more "usable water"?
200' of 3/4" garden hose? or 1 foot of 3/4" hose followed by 199' of 1" hose?
You can test the BTU capacity of various piping layouts using the calculators. Be careful not to undersize your reworked installation in an effort to reduce material costs.
cheers Bob
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What's the main reason for all this work? I've done enough black iron work to know that it's time consuming, and a bit of work. Is there some real advantage, like more ceiling space in the cellar so people can walk around?
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Christopher A. Young
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Stormin Mormon wrote:

Yes, the issue is about creating more ceiling space. This is in a 3-unit apartment building that I previously bought and have owned for a while. The lowest level apartment is in what used to be a partially below level "basement" with a high ceiling. But, when it was made into an apartment many years ago, they just left all of the pipes where they were hanging well below the joists and built a ceiling below that. Then someone else came along and apparently decided to remodel that apartment and added another dropped ceiling below that ceiling. I am re-doing the apartment above and I decided to just re-do the bottom level apartment at the same time. So, it has been completely gutted. Moving the hot and cold water lines up into the space between the joists will be easy. That really just leaves some large natural gas lines that I would also like to get up into the space between the joists. The end result will be a new apartment with a high ceiling.
The gas lines run from the front of the building to the back of the building where the boilers and hot water heaters are. The joists also run from the front of the building to the back of the building. There is a steel I-beam going across under the joists that supports the joists about 2/3 of the way back from the front of the building. So, raising the gas lines to go up in the joist space from the front of the building to the back (and above the steel I-beam) will not be too big of a deal for someone to do. But, the gas pipes seemed to be so large that I wondered if just replacing them with smaller size black iron pipe might make more sense while the work is being done. Now I'm thinking probably not. It may turn out that the best approach would be to have someone just add the right fittings and short peices of pipe at the beginning and end of each line to move them up into the joist spaces. One of the main gas lines is already there. It's just the other two that will need to be raised.
I do know that while that sounds fairly easy, dealing with heavy, threaded, black iron pipe and fittings can be a lot of work even for an experienced plumber.
Another option may be to have the incoming gas supply changed so that instead of it coming in through the front of the building, going through 3 meters which are already inside the building, and then running to the back of the building where the boilers and hot water heaters are -- maybe I could have the gas company route the incoming supply lines so they come into the building in the back. Then the gas meters could be located outside of the building in the back of the building and the gas supply would come directly into the space where the boilers and hot water heaters are. I am going to call them to ask about that possibility, and about what would be involved, etc.
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Of course, moving big black iron sounds like at least a two man job. I'm guessing it can be done. Would also new different hangers, to hang the pipe to the beams.
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