Gas line capacity with two sizes in same line

D107

As part of a kitchen rehab looking to correct and simplify gas piping. Gas comes into building at 3/4". From meter it's about a 50-ft run of 3/4" black pipe counting elbows and linear feet, etc.

--Just before entering boiler room it tees off into (probably the old original) 1/2" line which runs to the drier only. (want to cut/cap this one at boiler rm entrance.)

--The 3/4" line just after entering boiler room tees off to the boiler. Off that T another T runs a 1/2" malleable copper line about 10ft. to a direct hwh.

--The line past the boiler tee continues on --as a 1/2" galvanized--to the kitchen stove maybe another 8-9ft. What I want to do is tee 7ft down to drier from the line going to the kitchen. (Old drier line to be cut and capped.)

So there would be about a 50ft 3/4" run and about 25ft 1/2" run adding all the runs. So what natural gas capacity would this run have?

And I assume there's no downside to adding the gas draw of the 22mbh drier to the line beyond the boiler. Contractor says given 5.5" water column gas supply, the draw off the same line so close to boiler line shouldn't be a problem.
I have heard some Wallies say that it's best to have a dedicated line from the meter right to the boiler and nothing else; another dedicated line for other appliances should be run from meter.

I thought of doing this now since the gas line to stove has to be shifted a bit anyhow.

The current load is way oversized for the line with no particular problems that are evident to me: 340mbh. The lowest possible load I envision someday--removing the direct hwh and installing correctly sized boiler 1/4 the size--would be about 140mb, plus allowing for larger drier and maybe gas generator.

Thanks,

David

Brad White_185

Professionals

get paid for this kind of thing, David, so I would let them worry about it as they will be doing the work

Seriously, having 5.5 inches of gas pressure is nearly meaningless without knowing the flow rate. You need to know what your appliances need at the gas valve inlet under flow conditions. This is known as "residual pressure".

The other part is what total pressure drop your local code or utility dictates for the run.

The presence of galvanized and copper in your system is something that would not fly here in MA- your code may differ or you may be "grandfathered".

As a practical matter, the capacity is calculated segment by segment, tee to tee the entire way.

For your edification is one thing and there may be no issue whatsoever but your gas fitter will be able to walk you thought it when they do the work.

Al Corelli_2

Gas Line

If/When you renovate the basement, repipe the gas system.

Actually, if the 1st floor joists run front to back (I think they do), CSST or maybe even black pipe can be fed through to the front of the house. This can be done in 1.25 inch and then manifolded out where it comes through above the water heater.


It was nice to see you again. Are those adjustments working OK?

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D107

Thanks gentlemen;

Of course given the state of the art in the field today, I generally run what I'm told by new contractors through the Wall Verifier Machine. It was a licensed plumber who installed the galvanized run a few years ago, and I'm pretty sure that's not code in NY.

Yes, Al, thanks, system seems to be running fine; I can check DD/therms in a week or so and see if efficiency is up. Sort of miss that faulty fan center drone, though. Regret it took so long to find those Alan Mercurio knee pads for you...

Thanks,

David

Al Corelli_2

That's why I left the old one...

You can fashion a corded plug and just power it up to hear the drone if you wish..

Thank you again, David.

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