Natural Gas Pipe Sizing

[drozwood90]

I know this is not really home automation, but I have poked through Google and did not see any rule of thumb guides.

I found a nice chart to give me some numbers, but wanted to make sure I am interpreting the chart correctly...

Basically, we are building a new home. The builder insists that we only need 1/2" gas lines. In my LAST house, I installed a Tankless Gas unit, so I think I learned something. Based on the install charts (which are listed online)

http://www.boschhotwater.com/Portals/7/Tec...ish_10_2007.pdf
Page 19

(Side note, this was not my unit, but the chart is the same chart).

According to the distances that the builder gave me, I have about 55 feet of pipe from the meter to the furnace. Then another 10 to the water heater (for a total of 65 feet). Then another 42 feet to the gas line we are installing into the master bedroom for the fireplace...which is 107 feet.

I have normalized all the numbers to take into account drop distances (that is the water heater's 10 foot includes IT's 3 foot drop, but NOT the 3 foot drop from the furnace due to where it's T is located). I have also "guessed" at the number of 90s that will be used (as each 90 adds in ... I think it's 2 feet).

Since, they are ALL chained together (no branches, only taps along a long run), MY understanding is that you take the sum total of all the gas appliances that will be attached, and the FARTHEST point needs to be able to accommodate that amount of gas.

That, or you need to blend different sizes of pipe (as in 1" to the first appliance, 3/4" to the next, then 1/2" to the last). Which then the calculation gets more complex, but less costly...which I don't "get" as the cost difference between 1/2" and 1" pipe really isn't that MUCH...the nipples and Ts are more, but not THAT much.

So, am I crazy thinking that I need to have 1" lines? Based on the numbers that I have worked out, I need to have 138kBTU for my appliance, with capability for a LOT more (as a dead line I'm going to run will be for a GAS dryer (I use electric right now)) and I will be installing myself, a 55kBTU stove.

Did I get this out right?

Should I post all my detailed calculations??

--Dan

 

[nsisman]

When the gas fitters are there with all their machinery set up don't forget to do a drop for the gas fireplace(s) and also the gas bbq and possibly a gas fired pool heater and a gas dryer.

It would also make your home more saleable in future if you had a drop for a gas stove.

It's a lot easier to "tee" stuff in now for future use.

 

[upstatemike]

And what about a natural gas whole-house generator?

 

[pete]

alot of the calcs for gas piping depend on the pressure at the street . . I would at least place a call to a local plumber and/or the utility co and get their input as they will know the local system . .

did a quick google on gas pipe sizing . . there's lot's o hits

as far as mantaining max capacity to the end of the line, thats overkill, as long as the main can carry enough for everything downstream your good to go . .

thinking more about it and I'd bet your utility co will do the calcs for you if you give them the equipment requirements . .


Pete C

 

[DavidL]

A friend recently went through same deal. His home was set back a few hundred feet from the road. The per foot charge was a fair amount of money. When he told the utility company that he was going to put in a heated pole barn, a generator, etc. that upped the energy requirement to one inch line. The nice thing is that the way things were priced, the one inch line was "free" up to and beyond the footage that was required. So, he got a larger capacity for no money, vs. a smaller capacity for a fee. Go Figure.

 

[jhimmel]

As Pete already mentioned, the pressure in your area plays a role in the calculations. Low pressure gas service requires larger diameter pipe.
Also, some inspectors will not allow unused ("future use") 'T's in your installation.

 

[sda]

Since, they are ALL chained together (no branches, only taps along a long run), MY understanding is that you take the sum total of all the gas appliances that will be attached, and the FARTHEST point needs to be able to accommodate that amount of gas.

The piping to the farthest needs to accommodate the amount of gas for itself, the next farthest needs to accomodate itself and the farthest, and so on back to the meter.

meter----A----B----C

The piping from B to C is sized for the capacity of C. The piping from A to B is sized for the capacity of B+C. The piping from the meter to A is sized for A+B+C. Your service needs to be sized for everything being on at once.

You need to know the BTUH for each appliance and convert that to CFH. The typical conversion for NG is CFH=BTUH/1100. Determine the CFH and length for each segment and lookup the pipe size in a table such as http://www.tanklesswaterheaters.com/sizingtable.html . Doing this will give you a good idea whether the contractor is right, and if he's not and won't listen, be sure to point it out to the building inspector.

I think I read that most residential NG systems are 7"w.c. and appliances are designed for that pressure. It may come from the street at high pressure, but after the meter there's a regulator that steps it down. When looking at appliance specs for NG they call out a min of about 5wc and max of about 11wc. 1 PSI=27.68wc, which translates to min of 1/5psi and a max below 1/2psi. If you raise the pressure then you can use smaller pipe but need a special whole house regulator and regulators at each appliance. Obviously non standard design, probably more overall expense, and may not even be allowed.

Correct me if I'm wrong about any of the above. (As if I have to ask).

The alternative to black pipe is CSST. Its less labor intensive but more expensive in materials. There's some problems with it so read up first.

On a somewhat related note, has anybody done natural gas usage monitoring using a pulse output sub meter?
http://www.norgas.com/PDFs/Meters/GALLUS%201.0.pdf

 

[Herdfan]

Correct me if I'm wrong about any of the above. (As if I have to ask).

The alternative to black pipe is CSST. Its less labor intensive but more expensive in materials.

You pretty much nailed it. Slightly oversized will not hurt, but you don't want to starve your appliances by being under.


Just use black pipe. It is tried and true. All these new systems whether they be for gas or water or something else seem to end up in a class action suit. Go with what has worked for a hundred years.

 

[Sacedog]

Correct me if I'm wrong about any of the above. (As if I have to ask).

The alternative to black pipe is CSST. Its less labor intensive but more expensive in materials.

You pretty much nailed it. Slightly oversized will not hurt, but you don't want to starve your appliances by being under.


Just use black pipe. It is tried and true. All these new systems whether they be for gas or water or something else seem to end up in a class action suit. Go with what has worked for a hundred years.

Tell me about it. We were going to use PEX for water, and the city planning dept was requiring all kinds of liability waivers, manufactures specs, and certifications that the plumber is qualified to install it...we finally just said screw it, and went with tried and true copper pipe for our water. It cost about $1,500 more, but it was worth not having to screw around with the city.

 

[drozwood90]

And what about a natural gas whole-house generator?

I actually will be using a few floor scrubber batteries and inverters coupled with a transfer switch. Plus, the kick over time is MUCH faster on the battery system (the time the transfer switch takes to turn flip). Only certain circuits will be run from the x-fer switch.

I found that the payback was much higher and faster (I do not want to RUN off the generator/inverters, just have enough power for the essentials for a few days). Besides, if it comes down to it, I add in a generator (as the x-fer switch has a hookup for a gas powered).

I should also mention, that I was trying to just get the idea of how to run the calculations. I am actually planning for the first tap (furnace) to be able to handle a grill, dryer and a hot tub. I did not want to confuse the issue at hand.

--Dan

 

[drozwood90]

alot of the calcs for gas piping depend on the pressure at the street . . I would at least place a call to a local plumber and/or the utility co and get their input as they will know the local system . .

did a quick google on gas pipe sizing . . there's lot's o hits

as far as mantaining max capacity to the end of the line, thats overkill, as long as the main can carry enough for everything downstream your good to go . .

thinking more about it and I'd bet your utility co will do the calcs for you if you give them the equipment requirements . .


Pete C

I did the same search. If you look at the first few links, they are telling you how to calculate the actual diameter of the pipe, NOT for this type of configuration (star, linear, etc.) at this length, you need this diameter.

I have a chart that tells you the length/size/BTU, I just wanted to know, depending on my configuration, how to size the diameters.

--Dan

 

[drozwood90]

SDA, thanks! That's what I wanted to confirm.

I just wanted to make certain I was doing things right, as the builder stated that 1/2" was going to be adequate for everything. When I ran the numbers in how I THOUGHT it had to be ran, I came up with 1" for the first section, 3/4" for the next (if the grill goes there, it depends on WHERE the pipes end up in the basement, so that 3/4" might go back to 1/2"), then from that 3/4" tap, a T will go out to 2 1/2" lines (one to the stove, one to the fireplace).

Back at the front end, there should be Ts for grill, dryer, hot tub. That 1" line did NOT include load from a hot tub...so I might have to re-do that soon.

The good part is, they are only charging me $200 extra to run the line up into the master bedroom (I'll put in the fireplace). Then, since my washer/dryer is on the second floor one would think I should run that line as well as the house is being built. Actually I can get a line to there through the garage. So, I'm going to save the $$ on that for the moment (as I have an electric dryer).

Similar with the stove. They wanted $300 to put the line in for the stove...but only $220 for the master bedroom...which is strange, as the stove hookup is a cheaper hookup...but I digress. So, for the stove, I'll put my own pipe in (It's going to be nice to have a basement again!!).

I just wanted to make certain that my numbers that I came up with (1", 3/4"1/2") were not false, as I don't want to tell them they are idiots (ID 10 T errors!!) without making CERTAIN that I did this right.

I did the same thing in my last house when I put in my gas tankless unit. One contractor told me he's attach it to the existing line that was over there (1" at 35' could only handle the boiler). Luckily the BOSH install manual was VERY detailed and explained a LOT of things. When I asked the contractor about some of the warnings in the manual, he didn't seem to know...which made me uneasy. So, after I looked into it and found he was wrong, I did some calculating myself, and hired a different contractor. That contractor confirmed my numbers separately (he did his numbers and they were close to mine...which I showed him and he commended me on coming up with the numbers). I ended up running a second 1" line to get the necessary 175,000BTU to the tankless unit (which then the contractor hooked into my meter...I do not like touching those!).
After that, all was well!

It's fun to try to future proof the house! I may go with a 1 1/4" line to the first hookup just to have the loading ability there (if it's where I think it is in the house, that's the most central place and I won't have to try to add a second 1" line to the meter like I had to do last time.

--Dan

Since, they are ALL chained together (no branches, only taps along a long run), MY understanding is that you take the sum total of all the gas appliances that will be attached, and the FARTHEST point needs to be able to accommodate that amount of gas.

The piping to the farthest needs to accommodate the amount of gas for itself, the next farthest needs to accomodate itself and the farthest, and so on back to the meter.

meter----A----B----C

The piping from B to C is sized for the capacity of C. The piping from A to B is sized for the capacity of B+C. The piping from the meter to A is sized for A+B+C. Your service needs to be sized for everything being on at once.

You need to know the BTUH for each appliance and convert that to CFH. The typical conversion for NG is CFH=BTUH/1100. Determine the CFH and length for each segment and lookup the pipe size in a table such as http://www.tanklesswaterheaters.com/sizingtable.html . Doing this will give you a good idea whether the contractor is right, and if he's not and won't listen, be sure to point it out to the building inspector.

I think I read that most residential NG systems are 7"w.c. and appliances are designed for that pressure. It may come from the street at high pressure, but after the meter there's a regulator that steps it down. When looking at appliance specs for NG they call out a min of about 5wc and max of about 11wc. 1 PSI=27.68wc, which translates to min of 1/5psi and a max below 1/2psi. If you raise the pressure then you can use smaller pipe but need a special whole house regulator and regulators at each appliance. Obviously non standard design, probably more overall expense, and may not even be allowed.

Correct me if I'm wrong about any of the above. (As if I have to ask).

The alternative to black pipe is CSST. Its less labor intensive but more expensive in materials. There's some problems with it so read up first.

On a somewhat related note, has anybody done natural gas usage monitoring using a pulse output sub meter?
http://www.norgas.com/PDFs/Meters/GALLUS%201.0.pdf

 

[drozwood90]

On a somewhat related note, has anybody done natural gas usage monitoring using a pulse output sub meter?
http://www.norgas.com/PDFs/Meters/GALLUS%201.0.pdf

Wow! I've been looking for a sub-metering company! So, now the question is: How are the prices?

 

[drozwood90]

Correct me if I'm wrong about any of the above. (As if I have to ask).

The alternative to black pipe is CSST. Its less labor intensive but more expensive in materials.

You pretty much nailed it. Slightly oversized will not hurt, but you don't want to starve your appliances by being under.


Just use black pipe. It is tried and true. All these new systems whether they be for gas or water or something else seem to end up in a class action suit. Go with what has worked for a hundred years.

I also look at this this way:
It is a HELL of a LOT harder to drill into a steel pipe, then steel flex pipe!

--Dan