# 1/2" gas on Tankless?



## ZL700 (Dec 8, 2009)

Plbg Biz says: 

_*"2. If you believe the 1/2" gas input LIE started by Navien and now repeated by Rinnai, you should not be installing it."*_

It's not about the brand, hocus pocus, marketing or whatever for certain brands. Its about its burner and gas train requirements.

If you pay attention to some of the newer code book releases such as UPC, they have added the higher pressure drop charts to address these situations. Now we have not only 0.5" WC, and 1" WC N/G, but also charts up to 3" WC Pressure drop.

The purpose is not necessarily to address the main service, distribution lines, meters, etc. but the laterals feeding a specific appliance and its requirements.

Since Navien is mentioned, which is similar or better than many other European negative pressure style burner and gas trains found on many European boilers and now tankless we can use their example. Until the new Navien tankless came out it was for the most part the norm to require 6-8" WC N/G inlet pressures for them to function properly. Partly due to the fire rate capacity requirements, but also mostly due to their gas train pressure drops internal in the unit. Everyone knows, feed a Takagi or a standard Rinnai with 5" WC N/G and have it drop to 4-4.5" WC the burner goes out right? 

The newer and different style of burner technologies used in some appliances reduces or in some cases has eliminated the gas train pressure drop such as the Navien newer tankless and combi boiler allowing 3.5" W.C. inlet pressure to operate the unit at its fullest BTU potential. 

So take a 1" main home gas line at 5" W.C. (correctly sized from street, through meter and to this point) with a 1/2" side tap tee, once feeding a former 40K BTU hot water tank with 15' of 1/2" Blk T+C pipe, 4 ells and a tee. The pressure drop of the 1/2" line between the 1" and the new tankless unit upgrade would be about 1.25" W.C. That leaves about 3.75" W.C. N/G inlet at the Navien tankless meeting manufacturer requirements and allowing heater to work perfectly without cutting into the 1" line and changing the 1/2" gas feed.

That's why some units can use 1/2", no other reason than lower input gas pressure requirements. Save yourself some time, do the calculations, and if allowed use the 1/2".


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## plbgbiz (Aug 27, 2010)

Yes, the units will work great. It is the other fixtures in the home that fail.

A major part of the Navien training sessions I attended was diagnostics. A considerable amount of attention was on the subject of what to do if the burners on the stove go down or if the furnace is misfiring. Cause? New fangled burner sucking the gas out of an undersized system.

Straight from Naviens own mouth.


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## ZL700 (Dec 8, 2009)

plbgbiz said:


> Yes, the units will work great. It is the other fixtures in the home that fail.
> 
> A major part of the Navien training sessions I attended was diagnostics. A considerable amount of attention was on the subject of what to do if the burners on the stove go down or if the furnace is misfiring. Cause? New fangled burner sucking the gas out of an undersized system.
> 
> Straight from Naviens own mouth.


I see, maybe a wild mustang or a more of a mule? 

I only speak of the heaters technology and as said earlier it wont fix a total system capacity under load supply-

_The purpose is not necessarily to address the main service, distribution lines, meters, etc. but the laterals feeding a specific appliance and its requirements._

Thus if its on its own feed off of a proper capacity sized system, there should be only an acceptable drop on the 1" example. 

I have seen it and it will run on 1/2" gas line down to 1" WC (40% input capacity) The reading at the regulator didn't change much so the sucking part is false. The way I heard it told even with 3/4" supply rather than being restricted to about 15' with all the ells, total length with standard pressure drops, the 3/4" can be run farther with less pressure drop.

In the end its not about the pipe, but the minimal inlet pressure required. And since there is no internal gas valve, gas train or orifice pressure drop to account for the inlet pressure allowed is lower.


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## plbgbiz (Aug 27, 2010)

I'll preface this next with acknowledgement that you probably have a better handle on the technical aspects of this topic than I do. My knowledge is based on plumbing experience and manufacturers information. 

So...

1 cubic foot of gas=1,000btu

If a burner is rated at 150,000btu, then 150 cubic feet of gas is needed. Delivery pressure and pipe size are irrelevant to this equation. No matter the deliver system, without 150 cubic feet of gas, 150,000btu has not been accomplished. Granted, I may be over simplifying, but not by much. 

Notice the photo from Navien's install instructions. Since when does the order of fixtures in the system matter? Since the tankless companies realized a fundamental problem with selling their product. They marketed a money saving pipe dream that seldom if ever came true because of adding 100,000btu (or more) to the gas piping system in a home.

Solution? Re-engineer the gas valve so that it will draw more gas than the piping was designed for. The result is if a tankless unit is at the end of the pipe run, and demands 100,000btu over the original design, the stove and furnace have at least diminished function and possible complete failure. This is proven by Naviens own documented instructions.

Also, they say you can run 1/2" pipe but the minimum pipe size for the gas connection is 3/4". Why? Because the marketing department never has lunch with the engineering department. The instructions also acknowledge that while 1/2" is approved, you should not use a 1/2" flex connector because unwanted noise from the pipe is likely. Why is that? Because they are sucking more gas through a 1/2" pipe than it was designed to deliver.

The whole marketing scam with Navien (and now Rinnai with others to follow) is just that, a scam. They are just not good enough salesmen to convince me that 100,000btu-150,000btu of gas demand can be added to a system without increasing the pipe sizes from the new fixture back to the meter. It is plumbing 101.

On the other hand, they are probably more than qualified to sell it to the public and once again leave it to us to be the bad guys.

Next maybe we can discuss how Navien immediately voids the warranty if you have not tested and verified that the water conditions meet near Utopian levels of hardness, etc.


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## plbgbiz (Aug 27, 2010)

These are from the install manual also.

We were told that if a water test did not show these perimeters then warranty service would not be available.


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## ZL700 (Dec 8, 2009)

*Biz, I think you missed the point*

Of course you cannot run the whole house in 1/2"

Think of how many tank water heaters you run across with a 1/2" drop off 1"? Perfect retrofit there with no gas pipe work. 

The water quality chart is the same chart that every tankless company uses which based on the EPA National Secondary Drinking Water Regulations (40 CFR Part 143.3). Thats their suggested limitation for safe drinking water. I don't see that as a basis for a complaint. Check all other brands what I've seen they all use this same standard and it is high levels. 

If a customer has 12 grains hardness (over 200 ppm) for example they have other issues than worrying about getting tankless to last I would venture to state.

I'm interested in knowing how much you will be willing to spend for a 40-50 gallon water heater when 2015 changes are implemented. $1,200, $1,500?? What if they last as long as a cyclone besides?


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## James420 (Nov 14, 2012)

ZL700 said:


> Of course you cannot run the whole house in 1/2"
> 
> Think of how many tank water heaters you run across with a 1/2" drop off 1"? Perfect retrofit there with no gas pipe work.
> 
> ...



Are the new standards including water heaters under 55 gallons?


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## Logtec (Jun 3, 2018)

jonestribe10 said:


> no navien water heater sucks gas as you say they are a negative pressure gas system which allows them to work at a much lower supply pressure then your average equipment.we have installed many naviens in both residential and commercial applications including using the boiler to heat water source heat pump loops. theses are the most reliable units we have ever used. however we install clearwave ion inducers on all our installs and have never clogged a heat exchanger yet and our area has 16 t0 60 grain hard water. correct application and installation is the key to any equipment usage.


You sound like a robot!
…and you’re a lot late to the party..
the beer is gone, the chip bowls are empty, and the BBQ is empty and cold..
the only thing left is you and some drunk fat chicks.. enjoy!


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## Tango (Jan 13, 2018)

jonestribe10 said:


> no navien water heater sucks gas as you say they are a negative pressure gas system which allows them to work at a much lower supply pressure then your average equipment.we have installed many naviens in both residential and commercial applications including using the boiler to heat water source heat pump loops. theses are the most reliable units we have ever used. however we install clearwave ion inducers on all our installs and have never clogged a heat exchanger yet and our area has 16 t0 60 grain hard water. correct application and installation is the key to any equipment usage.


You have till morning to post an intro.


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## skoronesa (Oct 27, 2015)

Tango said:


> You have till morning to post an intro.


His morning or your morning? He's halfway round the world.


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## plbgbiz (Aug 27, 2010)

Wow, this is an old one.


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## Tango (Jan 13, 2018)

skoronesa said:


> His morning or your morning? He's halfway round the world.


Mine


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## skoronesa (Oct 27, 2015)

Tango said:


> Mine


I prefer Mine's.....


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