Gas piping install looks fishy

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joshpacker

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Any plumbers want to comment on the gas piping that was installed by my hvac guys to install a tankless water heater? I have a few concerns. And yes I should have inspected their work more thoroughly before they left.

To start it looks like I have at least a 1 inch pipe running to my meter. Originally, we had a regular tank water heater to the right of our furnace. We had both a 3/4 inch pipe going to each of these appliances with their own shutoff valves. Now, it looks like my hvac guys just came off of the piping for the furnace to supply the tankless water heater.

My first concern is that the original furnace shut off valve will now turn off gas to both tankless water heater and furnace, which doesn’t seem like it would be up to code.

My second concern is the pipe sizing. Looks like 1/2 inch piping concerting to 3/4 for the tankless. I tried to understand the part about pressure drops since that affects pipe sizing, but I still can’t determine if the 1/2 inch is fine. The tankless takes 200k btus. I’m not sure about the furnace.
ssouY6r
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All in all, does this look fishy to you guys? Should I talk to my hvac guys about redoing it?
 

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Dana

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Any plumbers want to comment on the gas piping that was installed by my hvac guys to install a tankless water heater? I have a few concerns. And yes I should have inspected their work more thoroughly before they left.

I'm not a plumber, but... (do engineers count? :) )

What tankless model is this? While some Navien units can get by with just 3/4" gas plumbing, most will need much fatter pipe to operate correctly.

To start it looks like I have at least a 1 inch pipe running to my meter. Originally, we had a regular tank water heater to the right of our furnace. We had both a 3/4 inch pipe going to each of these appliances with their own shutoff valves. Now, it looks like my hvac guys just came off of the piping for the furnace to supply the tankless water heater.

The typical burner on a tank is 35-40,000 BTU/hr (in) and doesn't modulate- it's either on or off. A typical tankless is 5x that much at max-fire (usually 2-5x bigger than a furnace burner too), and needs to modulate the flame to control the output temperature. Even if the gas piping is big enough (probably isn't- , most tankless units would need a dedicated home-run gas supply pipe teeing in as close to the regulator/meter as possible), A furnace turning on or off while the tankless is running creates a sudden pressure change at the tee to the tankless that can be interpreted as a fault condition by the tankless, potentially shutting it down.


My first concern is that the original furnace shut off valve will now turn off gas to both tankless water heater and furnace, which doesn’t seem like it would be up to code.

That's probably the least of your concerns.

My second concern is the pipe sizing. Looks like 1/2 inch piping concerting to 3/4 for the tankless. I tried to understand the part about pressure drops since that affects pipe sizing, but I still can’t determine if the 1/2 inch is fine. The tankless takes 200k btus. I’m not sure about the furnace.

A very short run of half-inch (a couple of feet) isn't a limiting factor, but the length of the 1" run to the meter (including "equivalent lengths" of all the tees & ells on the path), plus the total BTU draw at the tee are an issue:

gas_sizing_chart.jpg


Say the furnace draws 60,000 BTU/hr, the tankless is 200KBTU/hr, 260BTU/hr total, and the "equivalent feet" (linear + fittings) of the 1" pipe comes in at 40'. The chart indicates a 323KBTU/hr code prescribed limit, but even though your total load maxes out at 260K, the sudden fuel pressure changes from the furnace turning on or off can still interfere with the modulating tankless burner. With modulating burners, when your close to the limet, go one size fatter on the pipe, and whenever possible give it a dedicated run, not teed off to other big loads.


ssouY6r
5ZcPH63

All in all, does this look fishy to you guys? Should I talk to my hvac guys about redoing it?

Maybe you should be talking to them about redoing it, or finding a different, perhaps more competent contractor to handle it. If your furnace is way oversized with a big burner, with the addition of a 200KBTU/hr tankless you might even be over the rated capacity of your gas meter (it happens a lot.)

That said, some of the newer Navien models have internal compensation for pretty crummy supply plumbing and can get away with a lot of "stupid attacks" by installers (perhaps the most common being reusing the same 3/4" supply plumbing that the tank heater it is replacing.)

Again, I'm not a plumber, not a certified gas fitter.
 

Bannerman

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Table 1 on page 31 of the Noritz EZ111DV Installation Manual indicates 3/4" minimum NG feed line when the supply pressure is less than 8" Water Column. For many residential installations, gas pressure after the regulator located before the meter will be 7" WC.

The chart shows a 30' length of 3/4" supply could supply up to 199 cubic feet (199,000 BTU) so for a greater distance or any additional appliances such as a furnace, the pipe diameter will need to be appropriately larger.

Table 2 on the same page shows 1/2" pipe could be utilized to feed the tankless only when the gas pressure is between 8" - 10.5" WC.

Allowable pipe distances are typically based on smooth pipe, not the corrugated flex lines shown in your photos. In addition to corrugated offering a slightly greater flow restriction, high flow velocity through a corrugated flex line will often result in excessive noise.
 
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Dana

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When measuring the run length, add the equivalent lengths for every fitting in the path to the straight line lengths of pipe. Those turns really add up! eg: A single normal ell of 1" pipe is the equivalent of 5.2' of straight pipe, a single tee branch is worth 9.9'. It doesn't take many turns to boost 30' of pipe behave like 50' of straight pipe.

equivalent-length-screwed-fittings-feet.png
 

Sylvan

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According to decent plumbing practices

3/4" supply to each and reduced at the appliance

A induvial shut off for each appliance

Why decrease the supply and increase it again?

Hopefully they did not use white Teflon tape
 

Jeff H Young

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Without guessing at the sizing I would most certainly have contractor come back and completete job per code including sizing and ask him to walk you through your concerns all of which I think are valid.
After this if you like to tell us your pipe lenghts sizes and btu on appliances we can tell you min size pipe needed through out, plus tell us propane or natural draw it up
 

joshpacker

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Thanks for all the answers! Yes, I will talk to him and have him come back. To answer your question, I have about 50 feet of 1 inch pipe already going to the furnace room, which then splits off into the 1/2 inch pipes going to the furnace and what will be the future dryer. (I believe I was mistaken about the 3/4 inch before) The 1/2 inch runs are about 3 feet and 6 feet in length. It sounds like I really need another T from the 1 inch pipe to go to my tankless water heater with that being about 3-6 feet in length, and it sounds like it should be a 3/4 inch for this one.
 

Jeff H Young

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Thanks for all the answers! Yes, I will talk to him and have him come back. To answer your question, I have about 50 feet of 1 inch pipe already going to the furnace room, which then splits off into the 1/2 inch pipes going to the furnace and what will be the future dryer. (I believe I was mistaken about the 3/4 inch before) The 1/2 inch runs are about 3 feet and 6 feet in length. It sounds like I really need another T from the 1 inch pipe to go to my tankless water heater with that being about 3-6 feet in length, and it sounds like it should be a 3/4 inch for this one.

Wouldnt assume 3/4 will handle it or that 1 inch main is even big enough. It might even require a seperate 1 inch line all the way back to the meter. but whatever , you can either provide all details or be satisfied with what the contractor decides . Im not implying he wont do right , the 200,000 btu for the tankless is a lot , just a glance at the gas chart above suggests its more involved. 200k tankless, 80 k furnace 65k 35k clothes dryer Just guessing no bbq stub 380000 btu from the 60 foot column what size pipe is that? chart above suggests 1 1/4 pipe Im not breaking my book out at this point because Im guessing at a lot, but just a real rough look like you gotta run 1 1/4" main pipe back too the meter or a seperate 1 inch all the way to meter. I dont trust that chart or know which method sizing you use
 

Fitter30

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Call your gas company find out what the gas meter and their regulator is rated for. Also do have a gas cook stove and gas fireplace.
 

joshpacker

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The meter was already upgraded as I told my utility company I was planning to install the tankless 200k unit. I believe they upgraded it to 425k. But yes, I do see the 1 inch pipe is now questionable that would be currently supplying the furnace, tankless, and gas dryer.
 

Dana

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According to decent plumbing practices

3/4" supply to each and reduced at the appliance

A pipe that small is woefully inadequate supply for a 200,000 BTU/hr modulating burner for a run of any significant length, not "decent plumbing practice". The gas velocity required to deliver at a rate of 200,000 BTU/hr would result in a significant pressure drop over 50' (equivalent feet) of 3/4" pipe. Even if it worked it would make it hyper-sensitive to changes in fuel pressure as other appliances came on or off.

Decreasing it to 3/4" to match the tankless connection for a couple of feet just prior to the appliance is fine, it's not a long enough run to cause much of a pressure drop even though it's high velocity for that short section (emphasis on "short".)
 
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Dana

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Thanks for all the answers! Yes, I will talk to him and have him come back. To answer your question, I have about 50 feet of 1 inch pipe already going to the furnace room, which then splits off into the 1/2 inch pipes going to the furnace and what will be the future dryer.


Even if it were 50 feet of 1" pipe with even ONE tee (which adds 10 equivalent feet) and no ells in the path (not likely) it won't be enough to run a 200K tankless, let alone a tankless + furnace + dryer. Even if it were 1.25" or 1.5" pipe with a tees off to the furnace it's going to cause problems for the tankless if the furnace turns on or off during a draw of hot water.
 

Sylvan

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Normally natural gas is by volume not pressure . NYC for example any pressure greater then 1/2 PSI is considered high pressure chapter 4 2014 fuel gas code
 

Sylvan

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More gas piping with meters
 

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Sylvan

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Complex piping for sprinkler off domestic supply
 

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Jeff H Young

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Dont know what you paid the plumber for but I recomend piping per code. I wont install a tankless without figuring out the gas piping required size
 

Dana

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Normally natural gas is by volume not pressure . NYC for example any pressure greater then 1/2 PSI is considered high pressure chapter 4 2014 fuel gas code

And yet modulating burners on tankless water heaters are sensitive to both low pressure and sudden changes in pressure, yielding flaky operation (or even spitting error codes and shutting down) when near or beyond the typical pressure drop limits in the charts.

Table 1 on p.31 in the installation manual for the EZ111DV indicates 30' as the maximum 3/4" run for a 199K burner, assuming no other appliances being fed from the same run. For 1" that increase to 90' as a dedicated home-run line, but it gets a lot shorter if it's also feeding a 100KBTU/hr furnace near the end of that run.

Experience indicates that if the tankless is teed some distance from the meter on a line feeding other appliances they have fewer interaction issues if the tankless is the first appliance tee on the path (as shown in the examples on p.31), but even then flaky behavior isn't rare if the lines are close to the BTU limits in the charts with multiple big burners. With most houses a dedicated 1-1/4" line for a 199KBTU/hr tankless is very reliable, or even 1" when there are comfortable BTU margins. Sometimes boosting the pressure at the main regulator at the meter can fix those issues, other times not.
 
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