Question about gas line sizing...

Skyline

A quick background of the system in question...

The system in question is located at my daughter's house, where she used to have a Navien combi-boiler. It had its share of issues, prior to being replaced by the Lochinvar NKC199 boiler eight month ego.

Couple of days ego the new boiler failed as well with "flame failed" error; resetting the boiler fired it up and did not fail again. The service guys came to identify the source of the issue and fix it. They checked a number of things, pulled the igniter and the other thing was probably the flame sensor. The parts were just fine and they did a combustion test that passed with "flying colors".

They suggested that, in random order:

1. the gas line is undersized
   
2. more than one appliance is used at the same time
   
3. the meter may not supply the right pressure
   
4. everyone in the neighborhood had been using their gas appliances at the time of failure, that may had dropped the NG pressure in the area
   

The house has two gas appliances, the boiler and the gas stove, here's a rough drawing for the gas line:

The gas stove was not used at the time (around 17:30) the boiler had failed with the error. Based on this chart:

The 3/4" pipe cannot supply sufficient amount of gas for the boiler running at full capacity, but... The gas meter has 1/2" piping in/out, while the boiler gas line is also 1/2". Questions....
Would replacing the 3/4" line with 1" line alleviate the issue described?
Are 1/2" lines the limiting factor?
Could the gas meter be somewhat worn out and should be replaced?
Could the incoming line's pressure drop on the gas meter cause this issue?

TIA...

Ironman

You didn’t show the length of pipe between the boiler and the Tee, but assuming the total developed length is 30’, then the line is too small.

Depending upon the total developed length, it looks like that you’d need at least 1” black iron between the meter and the Tee. If it’s CSST, then it would have to be at least one size larger.

Or, you could have the gas co. Install a 2 psi meter and step down regulators at each appliance.

A minimal amount of 1/2” pipe at the appliance is acceptable, but it shouldn’t be smaller than the appliance’s connection size.

pecmsg

Did the tech test the pressure at the meter, at the furnace with everything calling or did he ASSUME there's a pressure drop?

You don't say how many T's, Ells, 45° fittings are in the runs. I would rather see 1" from the meter to the T but thats a guess from here.

EdTheHeaterMan

I would use 1-1/4" from meter to boiler. Then drop to a 3/4" short appliance connector for the last 2'


in my example 1" will only feed 157,000 BTU boiler on that natural gas chart. Your boiler needs 199,000 on full input.


CSST would have less capacity but in my example you would still be OK with 1-1/4"

You could go with smaller pipe if you sized on a higher gas pressure from the meter to allow for 1.0" Pressure drop. That means for the pressure at the gas valve inlet to be the same, the pressure at the gas meter regulator needs to be higher.

Skyline

Thanks guys...

The tech did not test the pressure, just stated that he suspects, the 3/4" gas line might be too small for the boiler. Which resulted in my statement of "Now you tell me this, where were you when you guys gave me the quote for the boiler replacement?"
The 1/2" pipe is in the boiler, so is the wiggly 1/2" pipe coming out of the gas meter that connects to a 1/2" to 3/4" elbow or whatever it's called.
Darn, I forgot to add the fittings to the calculation. From the gas meter to the 1/2" line in the boiler, there are four fittings and the actual total pipe length is 23'; the pipe is solid black iron pipe, no flexible connection in the line. The total length for BTU rating is 43' then, that calls for 1-1/4" gas pipe to the "T" and the 1/2" pipe in the boiler. That would be more than sufficient for the maximum of 200K boiler. Even if my calculation with the fittings is off by 5-10 feet, correct?
I'd just hate to go through this process just to learn, that the gas meter is malfunctioning. After all, this issue came up only once in eight month, or once in a blue moon. It's not really the money that it'll cost, it's more of a headache, scheduling the work and being there.

EdTheHeaterMan

The only time you need full capacity of 199,000 is when the boiler is operating at full capacity. During the warmer weather times, you may not actually get the boiler to full capacity. I believe the entire country went thru some unusually cold weather for over a week during the Christmas season. Is that when the problem happened?
or is this the first time you have experienced the Failed Flame error?

There are charts that will allow for a 1.0" WC pressure drop and even 2.0" WC pressure drop with much smaller pipe. The thing is... to use these charts, you must have elevated pressure at the meter in order to get the same minimum pressure required at the appliance. If the gas pressure at the street drops as a result of additional customer load during lower outdoor temperature, that can reduce the inlet pressure to the gas regulator at the gas meter. This is unlikely, but can happen. Another problem is that outdoor temperature can sometimes play tricks with outdoor regulators and gas meters. This is why you need to have the proper gauges on the appliance when the problem is happening to determine where to look.

To just replace the pipe with a larger pipe without knowing the actual pressure at the appliance when there is a problem is just crazy. It brings me back to my mantra "After you finish the expensive repair and you have the same problem, what will you check next?". I believe that you have a small diameter gas pipe, but I would verify before recommending replacing it.

ratio

Skyline said:

…The 1/2" pipe is in the boiler, so is the wiggly 1/2" pipe coming out of the gas meter that connects to a 1/2" to 3/4" elbow or whatever it's called.

I'm sorry, do you mean that the ½" pipe that connects the meter to the rest of the gas piping is some kind of flexible pipe? Can you post a picture of it?

Skyline

@EdTheHeaterMan - I just love how the pros provide in depth analysis of the issue at hand, thanks Ed. One of the reason why I keep reading this forum, learned a lot about heating even if I wouldn't pass as an apprentice in field as of yet.
This is the first time that my daughter's boiler had the error and it didn't happen during the cold snap around Xmas. It has taken place during the past Sunday, or Monday at 05:40PM:

At the time the gas stove had not been used, it was only the boiler running, rather failed. Since resetting the boiler, there had not been another failure.
While the tech did bring up the issue of pressure drop due to additional customers, that may or may not be valid. Although her house is a half a block away from a small shopping center with couple of restaurant and couple of apartment building with 4-5 floors. Anything is possible at this point I guess...
Could this error be caused by voltage fluctuation, be that by slight surge, or brownout? The control board in the boilers nowadays are just as sensitive for voltage fluctuation as computers and other electronic equipment. Maybe the igniter did not have the right voltage and could not start the boiler. I did add a surge protector for the boiler on past Wednesday and her electrical panel does have a whole panel surge protector. Maybe I should add a UPS to protect against brownout as well.
I do believe as well, that the current gas line size is too small for the maximum capacity of the boiler and sooner or later it will need to be replaced. That's regardless, if there might be other issue that actually caused the recent "flame failed" error.
That's the thing, my daughter is rather frugal when it comes to money. Unless the source of the issue is clearly pointing to the size of gas line and this issue becomes frequent, it's unlikely she'll go for replacing the gas line. While she's frugal, she picked the second highest bidder from list of candidates. While I pushed for a Viessmann boiler, like mine, she couldn't justify the 20-30% cost increase.

@ratio... It is not a flexible pipe on the meter, it's like mine in the picture below. Unlike mine, her gas meter is in the basement with no heat, where the temperature is around 65-68 degree Fahrenheit.

I don't know what the proper name for the fittings circled in red...

TonKa

EdTheHeaterMan said:

The only time you need full capacity of 199,000 is when the boiler is operating at full capacity.

Aren't many modulating boilers designed to light at 100%, run for a short bit, then modulate down?

Ironman

TonKa said:

EdTheHeaterMan said:

The only time you need full capacity of 199,000 is when the boiler is operating at full capacity.

Aren't many modulating boilers designed to light at 100%, run for a short bit, then modulate down?

No, most ignite at 30-50% and then drop to their lowest modulation for two minutes before ramping up.

ratio

Skyline said:

@ratio... It is not a flexible pipe on the meter, it's like mine in the picture below. Unlike mine, her gas meter is in the basement with no heat, where the temperature is around 65-68 degree Fahrenheit.

I don't know what the proper name for the fittings circled in red...

Ok, that's a plain old meter setting, nothing to worry about.

Skyline

@Ironman... The initial ramp up could be dependent on the brand name. I observed a number of times that my Vitodens 222-F starts up as high as 70+% burner capacity when the thermostat calls for heat. Afterward it is modulated down to as low as 15 - 17%, but the start up capacity utilization does depend on the RWT.

The combi-boiler, like mine, might be working differently from heat only boiler. Supplying hot water with my Vitodens usually runs at 95 - 98% capacity, when my wife is taking her long shower...

Ironman

That’s the meter rack.

BobZmuda

What was the output of the previous boiler?  

 you could test the line sizing theory by having them limit the combustion rate for heating.  If she needs 180,000 btus an hour for heat loss at those temps then that is not going to be an option for testing.  

Since she had a combi before I’m going to suspect that it was oversized for heating in order to be sized correctly for heating her domestic hot water.  The only way to know is with a heat loss analysis. 

She may not have ran into the pipe sizing issue while heating dhw with those outdoor temperatures and if she never fills a bathtub. The dhw btu requirements are based on flow and how much temperature rise there needs to be. 

Also, given this company’s performance i have to ask this question.  Did they install an outdoor reset and set up the temperature curve?  That’s imperative for efficiency with this boiler. 

EdTheHeaterMan

The RED circles indicate 3/4" ID pipe fittings that are not usually counted as fittings in the pipe length calculation

While the tech did bring up the issue of pressure drop due to additional customers, that may or may not be valid. Although her house is a half a block away from a small shopping center with couple of restaurant and couple of apartment building with 4-5 floors. Anything is possible at this point I guess...

Well considering that Sunday, January 22 was National Hot Sauce Day and the Chinese New Year, If the majority of the residents of the apartments were of Chinese decent and the restaurants were offering specials on items that contain Hot Sauce, there may have been an unusual demand on cooking with natural gas, then all the gas was being over-used and could not get to the Lochinvar Knight in your home. If you had partaken in the Hot Sauce slathered items from the restaurants, perhaps you could have provided your own natural gas. Although I am not sure how you hook up to that source of fuel.