Question: Gas Line Sizing

[Tidybuoy]

I'm getting ready to install my tankless water heater and my neighbor (who is a licensed plumber) will assist me making sure we get it installed properly. I have a question about gas line sizing. I currently have not yet calculated the requirements but I am wondering a couple of things in advance:

Let's say my tankless ends up requiring a 1" gas line. 1) why is the input to the water heater only 3/4"? Doesn't that defeat the 1" issue?

2) my house has a 1" gas line running under the house with 3 1-inch branches which then drop down to 3/4" near the appliances (with the exception of my "tanked" water heater which drops to 1/2".

If the branch nearest the new tankless converts down to 3"4" less than 6 feet away from the new water heater location, would I need to modify the line so that it is 1" diameter all the way to the water heater and then converts to 3/4" at the last 6" of line?

I guess my confusion is based on a possible 1" requirement that will ultimately be reduced to 3/4 at the appliance itself. I'm guessing the 1" requirement means that the line can hold more quantity which will be available as the appliance needs the gas and the 3/4" input will not be overly restrictive. I'm just trying to educate myself before the actual calculations and installation.

Last question: The tankless requires a sediment trap on the gas line, near the appliance. Why don't any of my other appliances have a sediment trap (i.e., heater, stove, and original water heater)?

[908/930]

Here is my take on it, I am not a licensed gas fitter.

The larger diameter line is to avoid flow/pressure loss over longer distance, not sure what pressure your natural gas is out there but prob between 3/4-3 psi. Like with air lines a smaller fitting can be tolerated at the end.

You will need to know what pressure you are starting with and BTU of the heater to determine if the 3/4" dia line for 6' will carry enough flow or require changing up. Your neighbour should be able to determine this.

All the gas furnaces and water heaters I have seen have a trap in front of the unit, likely code requirement.

[Bill Douglas]

Not a gas man. But what I gleaned from the conversation with the man is it's about the gas meter and the psi/flow rate it lets through. He was working out which model meter I needed for two big gas heaters and gas hot water. He didn't want to know about pipe diameters.

[Zeke]

908 is correct. A pool heater only uses a 3/4" fitting at the heater, but since the heater itself is usually located a good distance from the house supply, the plumber will tap the meter with a 3/4 and then immediately use a reducer to a much larger size, depending on the distance to the PH. I've seen 2" a lot. Even 2 1/2".

[BK911]

Yup.
Incoming pressure, appliance required pressure, mbh, and length of pipe all figure into pipe size.
Pressure you have at non running appliance will be greater than pressure when appliance is running.
Depending on length the difference may be unnoticeable.

[Tidybuoy]

I'm guessing this is a similar concept as a fuel rail on a fuel injection system where the the rail holds a supply of gas available when the injectors need it and combined with the damper, prevents surges.

Although this is totally different, I'm guessing the larger line holds enough fuel so that when the tankless fires, it's not relying on a more limited supply that a smaller line would hold. Regardless, I will make sure we size the lines correctly based on the mathematical calculations on output of the meter and requirements of the appliances.

[red-beard]

It is about flow. To get flow through a pipe, you need differential pressure and pipe size. Bigger pipe means smaller differential pressure. And the appliance needs a certain amount of pressure at the input to work.

Gas in this country is regulated to 7-11 in Water column before entering the house.

See here, a small online calculator

https://www.engineeringtoolbox.com/natural-gas-pipe-calculator-d_1042.html

The only thing, you need to know the units (inches of water - pressure) to use the calculator.

On a Pool heater or generator, the "smart" thing to do is to run the pipe to the heater at 2 psi and then put the regulator, 7-11 in-H20, right at the "appliance". You cannot do that inside. If this heater can be outside, this is eezy-peezy. Run the pipe at 2 PSI and put the regulator right in front of the heater.

How many BTUs/per hour is the heater rated? Divide by 1000 and it needs that many cubic feet per hour of natural gas.

The biggest one I've found at Home Depot is about 200,000 BTU/hr.

So, 200,000 BTU/hr = 200 cu feet/hr

If it is inside, on a 3/4 pipe, if you have 50 feet of pipe, you will lose 2.3 in-H2O pressure from the input to the output. With 1", the pressure drop will be 0.45 in-H2O. Most of the time, you will be better off with the lower pressure drop. See if he can run the pipe as 1" flex line.

Also, make sure the meter can supply the needs of the Hot Water Heater and all your other appliances. Most of the time when we install a NG generator, the meter needs to be upsized.

[Tidybuoy]

It's looking like I will have to upgrade my meter. Can someone here, with expertise, confirm my calculations:

Gas Line is 1" for a total of 84'.
The 1" line is run to each appliance (under the house) and then converted and passed up the wall to the appliance:
1/2" for furnace @ 3'
3/4" for stove @ 1'
3/4" for Tankless @ 4'

Furnace: 100,000 BTU
Tankless: 199,900
Stove: 56,200 (all 5 burners)
Total 356,100
divide / 1000
356.1 Cubic Feet per hour (Max Demand)

Meter 210 C.F.H (@ 1/2" Diff ??)

PG&E Meter:


Question:
Is it ok for me to complete my installation before calling PG&E? I'm trying to get this done so that I can schedule sheet rock installation. I won't use the furnace for about 6 months, and I can refrain from using the stove and definitely will not be using all 5 burners at the same time. I also don't want the project to be in a state of disorder when PG&E comes out as they may inspect the appliances.

[Tidybuoy]

Each Appliance Specs:

Stove:


Furnace:


Tankless:

[red-beard]

Your calcs look correct. You need the next size up gas meter.

[Tidybuoy]

Originally Posted by red-beard

Your calcs look correct. You need the next size up gas meter.

I failed to give you credit in another thread but thank you for pointing this out. I would never have thought to check on meter capacity and my plumber friend never thought of it either. It's always good to do your own research IMHO.

[red-beard]

My parents just went through this. The meter plus stove were barely in the capacity of the meter. But the meter was old. Changed meter and the tankless worked fine.

While it is unlikely you will hit all the appliances at the same time, it is good to have them match.

[look 171]

I had to up my meter because I built a natural gas fire pit. Gas company came out and installed a larger one for free. Call and ask, you never know?

[red-beard]

When I installed my pool heater (400,000 btu/hr), it required an upgraded meter. I think I had to "donate" $275 to the gas company

[look 171]

Originally Posted by red-beard

When I installed my pool heater (400,000 btu/hr), it required an upgraded meter. I think I had to "donate" $275 to the gas company

I really think I got lucky on that. We were chit chattin' about bicycles because I was cleaning mine outside when he arrived. I noticed a bunch of meters in the back of his truck and he did a quick calc just to make sure I was in line within specs. Next thing I knew, he installed a larger, new meter on there, wave to me and left.

275 aint bad if you ask me.

[red-beard]

Not compared to the $45K for the pool.

[Tidybuoy]

My Gas Pipeline re-location is complete and I passed the leak test! This was a job I don't want to repeat. I've been under the house about 50 times this past week and my stomach muscles feel it. I may have even lost a pound or two.

Although I was only moving the gas line a couple of feet to a new room, everything was connected in a way that I had to undo several elbows and tee's. Basically, I had to re-do the gas line to all appliances. In addition, I ran a line up the wall to the attic for the future relocation of the furnace to the attic and moved my stove to the other side of the room so re-plumbing the gas line was required.

My neighbor who is a retired plumber helped me with doing an overnight pressure test and NO Leaks! I also did the bubble test at all connections and I purchased an electronic leak detector. I will say, the electronic gadget leak detector was only $26 and seems to work well as I tested by opening the gas valve very slightly to simulate a leak and it registered a leak from a few feet away with only a miniscule amount of gas let loose.

Now to finish the plumbing which is half done. Fortunately, soldering copper to size is much easier than all the measuring, cutting, threading of the gas line.