I'm looking at extending my existing gas line to the other end of my basement. The line comes into the house as 1" but doesn't go completely to the other end. I'm looking at around 40' of pipe to run.
I only need 3/4" on the other end, so I'm not sure what's the better option here in terms of pressure, supply, and cost. The current 1" line ends at a T with 3/4" going down to my furnace and 1/2" running forward about 10' and then up to my kitchen range. So I'm guessing in theory I could remove the range line (replace the T) and extend out from there with my new line. Then closer to the range T up to reconnect the 1/2".
So with that; should I extend on with 1" line and just connect up my 3/4" at the end and the 1/2" at the first third of the line, or extend with 3/4" all the way to the end and again reconnect the 1/2" where it goes? So generally, do I downsize the line to reach the end or extend what I've got? Will either help or hurt the pressure, supply, etc.
I do know that the difference in cost of the pipes themselves will be around $7. So I'd save $28 by running the 3/4". But is it better to run the 1" so that more could branch off of it later on if needed?
Best Answer
When designing gas distribution systems, one must consider the demand of every appliance in order to find the minimum pipe sizes.
But, to answer your first question, there is little disadvantage in using larger pipes (except for cost and space). It is very likely that the 1 in pipe will be sufficiently large.
The calculations needed require you to know the lengths of the pipes and the amount of gas used by each appliance. Also, you need to know the gas pressure fed into your system, and the required pressure at the appliance. For low-pressure gas systems (like are in most houses), pressure drops linearly with distance. Tables (generally in the fuel gas/housing code) state the pressure drop per distance with various pipe sizes and flow rates.
So, one consults these tables and calculates the pressure delivered to each appliance with your pipe configuration (assuming that all appliances are operating simultaneously). If the delivered pressure is above the minimum required, then all is well.
The relevant regulations (including tables) are copyrighted, so I'm posting them here. They are likely available in your local library.
Be sure to read up and follow all relevant regulations, including performing a pressure test of the newly installed pipes, in order to ensure that the installation is safe. (Also note that high pressure testing will damage regulators in your appliances, so close their shut-off valves before the test).