Pipe Sizing for Natural Gas

[@Anthony-oq8gc]

This is incorrect. 2:38 time stamp. You remain using the longest run measurement to size every branch (unless a there is a new meter, or regulator). Therefore, to size the boiler, it should be 70’ as longest run and 180,000 btuh, leaving a pipe diameter of 1” (according to the chart you provided)

[@MrFrankFixIt]

Thank you for your comment. If I am understanding you correctly, you are saying that I should have used 70' in by boiler calculation instead of 12'. However, I disagree because the boiler is not in series with the other appliances, it is in parallel. I see three parallel branches: Branch 1: Water Heater, Branch 2: Boiler, Branch 3: Fireplace & Space Heater (in series with each other). Using the longest run method in a parallel configuration, you need only account for the length from the meter to the parallel appliance. That said, I see now that I DID NOT use the longest run in Branch 3 for the Fireplace drop. Fortunately, half-inch is still correct. Please note that I made this video as part of a class assignment when I was a student first learning about gas sizing. I should re-make this video to detail my current sizing method (using formulas instead of charts) and explain pressure drop as well as equivalent length for fittings. I should also include a comment about the calculation differences between rigid pipe and CSST. Perhaps one day. Honestly, I didn't think this video would be as popular as it is. Again, thank you for your comment. -Frank

[@edonismajlaj2948]

Good job buddy great explanation

[@fredwild190]

Clear and concise. BUT, what happens when it's time to ADD a drop to an existing piping system? Suppose, for example, you wished to supply a gas dryer (20,000 BTU/H) between the tee to the fireplace and the space heater? I expect it would prompt a recalculation of the entire piping system and a determination whether the piping to the new drop is sufficient to the purpose. In fact, the basic piping system might be insufficient to the larger total demand, or perhaps, the dryer might drop from another location with a greater or excess supply.

[@boby115]

I have been in the natural gas utility industry for over 35 years and would like to give you the highest compliment on your video ( you did your homework)👍. Most videos are pretty accurate until they get to sizing drops and for some reason they continue to use the total length in their drop calculations ( it doesn't hurt anything it's just a waste of time and material, especially when we get into the larger homes and businesses). In the real world it's quite the opposite the main lines (trunk lines ) are found undersized & the drops are okay. I'm assuming your eye for detail comes from an engineering background (?). Keep up the good work; regards Bob.

[@samconstruction4275]

Thanks very helpful

[@vicu2805]

Thank you for your video. May I ask if you have a video with a branch that goes up to, say, the roof? Thank you.

[@MrFrankFixIt]

I am not aware of any differences in sizing calculations for vertical runs.

[@robertwardi358]

Thanks brother

[@rahuljaiswal4421]

How can we calculate the inlet pressure? Also how you are taking 0.5 psi pressure loss

[@MrFrankFixIt]

Inlet pressure, that is the pressure supplied by the gas company's regulator, is measured with a manometer, not calculated. Typically, this is around 7 inches of water column for natural gas and 13 in. WC for propane. Managing pressure drop is the goal of pipe sizing. 0.5 in. WC (not psi) is a conservative estimate and the go-to number used on most exams. However, this number is calculated by measuring the supply pressure and comparing it to the minimum pressure required by the appliance. The minimum inlet pressure will be stated on the appliance data plate. For example, if the inlet pressure at the service regulator is 7 in. WC and the minimum pressure required by a water heater, for example, is 6 in. WC, then the pressure drop sizing chart you should reference is 1 in. WC. You will note that as the allowable pressure drop increases, the required pipe diameter decreases.

[@ashgangman2312]

Hey is this the right method because the way my teacher taught me is to keep the code zone the same throughout

[@MrFrankFixIt]

I'm not sure what you mean by "code zone". Can you give an example?

[@parentswhocare2950]

From an engineering perspective, this doesn't work correctly. The point of calculating the longest length with all appliances is to calculate the mainline diameter to ensure it will carry enough gas. Once that's calculated, each branch only needs to be calculated back to the trunk, or branch that was already calculated to have enough gas capacity. There's nothing special about the meter location -- it's simply where you know you have a certain flow. Once you've calculated the first 4' leg at 1-1/4, you can assume the meter is now AT the first junction, right? So now it becomes a 12' length to the boiler since you know there's sufficient gas up to that junction already. I understand why it seems convincing to calculate runs all the way back to the meter, but that's theoretically like actually having, say, a 1/2" pipe going all the way from the meter to the space heater. Perhaps thinking it's like having a 1/2 inch pipe inside the 1-1/4 inch pipe. But that's incorrect because the 1/2 inch pipe has different friction loss than carrying that same volume in a bigger pipe. If you use the actual pressure drop formulas instead of the chart lookups, you'll find that the capacity is much higher because of the initial trunk size. An easy way to see why the method you showed falls apart is imagine you split out additional outlets right at the space heater and added 4 of those space heaters instead, maybe adding a couple more feet to each. So now each has a total length back to the meter of say 70'. The total draw hasn't really changed significantly so the 1-1/4 from the meter is still sufficient. And 70' at 1/2 inch is sufficient to feed each individual heater. But then notice that the total run of 1/2 pipe you have from the space heater back to the 3/4 line is 57'. That length of 1/2 pipe can only carry 66 CFH total. Yet you have 33 CFH going to the fire place, plus 72 CFH more going to all the space heaters. There's no way that the 11 foot 1/2 line that splits from the 3/4 is going to be carrying enough gas for what's downstream. The right way to compute this is to determine max CFH at each junction, and decrease that each appliance pulls that number down. Like I said, it's more complicated but correctly accounts for more complex situations. Your approach works for many common layouts, but as soon as you have several appliances after a long run it doesn't work anymore.

[@21gonza21]

Couldn’t you just run a 1 inch pipe to the longest run then branch out 3/4 to the appliance

[@MrFrankFixIt]

No. A one-inch pipe diameter can not support a 271,000 BTU/hour load. The total load is the total load regardless of the number of branches and/or drops. Even if the run to the farthest appliance was 60 feet, one-inch pipe can only support 257,000 BTU/hour. However, what is the likelihood of all the appliances demanding gas at the same time. Currently in my case, there is a 0% chance because I have removed the natural gas fireplace insert. Therefore, I could extrapolate from this table that for a run of 64 feet, a one-inch diameter pipe could support 249,000 BTU/hour, which is greater than my current maximum demand of 241,000 after removing the NG fire log. To ensure that all appliances receive enough natural gas, it is important to follow this method and comply with local ordinances.

[@21gonza21]

@@MrFrankFixIt understand, do you know if you can pressure test the line right after installing or do I need to let the soft set sealant cure?

[@MrFrankFixIt]

@@21gonza21 Check the manufacturer's label. Blue Monster, for example, does not have a set/cure time and thus, can be pressure tested immediately.