Thread: Double tapped gas supply

I want to spark this discussion mostly because I want to learn more about gas plumbing,(sizing supply lines, use of flex lines) and I want to hear what others have to say on this subject.
Also because I cant remember where I read it but I am quite sure you cannot T off of the branch going to the furnace. It is a dedicated supply. Right?

The first photo is obvious. They have a T at the furnace supply. The second photo is at the 90 degree elbow above. There is another flex line tapped off of it. Both flex lines run through the finished basement ceiling to the other side of the house(more than 20 feet) to service a gas fireplace (18K BTU) and gas stove (20K BTU). The last photo is the connection at the gas fireplace. I know that the supply line should be black iron where it enters the cabinet of a furnace. Does that also apply to gas fireplaces? Is that only required in seismic areas?

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As long as the supply pipe heading towards the furnace is large enough to handle the demand of the furnace, and the other appliance, all should be fine.

Where most people mess up is the furnace gas supply pipe was sized and pipe only to run the furnace, and they tend to take the drip leg off and pipe in a new appliance. So they are making two mistakes, one you are not allowed to use the drip leg, and they are now exceeding the demand for the size of supply pipe.

Getting into gas pipe sizing, is not as simple as looking at what you have right at the fixture. You have to investgate the whole line from the meter, down the main trunk, and the branch lines to the fixture/applance.

The appliance shut off valve is usually before the drip leg. Wonder if it got moved when the tee was added..

Bill,
There are a lot of factors that determine gas pipe sizing. In most residential settings, the gas is delivered at low pressure, typically one half PSI.

Pipe sizing is based on standard demand tables found in most plumbing codes. The system is designed "backwards" in a sense. Starting at the farthest demand, the total demand for the system is added up, working back towards the source and that determines the size of the pipe leaving the meter coming into the house. Each branch line demand is determined,he and again, a chart in the plumbing codes will tell you what size pipe you need to provide that demand.

If you don't have the standard "demand chart" you can calculate the demand in CFM (cubic feet per minute) by calculating a factor based on the BTU rating found on the device's data plate. Check with your local gas supplier to see what the calculation factor should be for your area.

As an example: a 100,000 BTU gas furnace would calculate out to be approximately 91 CFM here in the Southern California area.

Back in the day, when I was a working plumber, one did not oversize gas pipe since it wasn't exactly easy to cut, thread and fit up larger piping. There was also the expense factor. Probably 99% of gas piping systems were sized to meet the existing demand. Tapping off at the end of a branch totally blows all of these carefully performed calculations. This can lead to "starving" both appliances at this location causing several unintended consequences, including faulty combustion which produces excessive carbon monoxide.

All of this is way beyond the SoPs of any home inspector association and should be left to a qualified licensed plumbing contractor.

Thanks to all for the input. Makes a lot of sense. I'm still wondering about the flex line going into the fireplace cabinet. Is that alright or should it be black iron? Also can you run long lengths of flex line through a finished ceiling. Unless the flex line is manufactured in lengths longer than 20 feet, It seems safe to assume there are concealed fittings somewhere. I wrote what I observed and recommended further evaluation by a licensed plumber.

That's not a flex line, that's csst, and it is ok to go directly into fireplace since it is a fixed appliance and not moveable.

Originally Posted by Dana Bostick

Bill,
There are a lot of factors that determine gas pipe sizing. In most residential settings, the gas is delivered at low pressure, typically one half PSI.

Pipe sizing is based on standard demand tables found in most plumbing codes. The system is designed "backwards" in a sense. Starting at the farthest demand, the total demand for the system is added up, working back towards the source and that determines the size of the pipe leaving the meter coming into the house. Each branch line demand is determined,he and again, a chart in the plumbing codes will tell you what size pipe you need to provide that demand.

If you don't have the standard "demand chart" you can calculate the demand in CFM (cubic feet per minute) by calculating a factor based on the BTU rating found on the device's data plate. Check with your local gas supplier to see what the calculation factor should be for your area.

As an example: a 100,000 BTU gas furnace would calculate out to be approximately 91 CFM here in the Southern California area.



Back in the day, when I was a working plumber, one did not oversize gas pipe since it wasn't exactly easy to cut, thread and fit up larger piping. There was also the expense factor. Probably 99% of gas piping systems were sized to meet the existing demand. Tapping off at the end of a branch totally blows all of these carefully performed calculations. This can lead to "starving" both appliances at this location causing several unintended consequences, including faulty combustion which produces excessive carbon monoxide.

All of this is way beyond the SoPs of any home inspector association and should be left to a qualified licensed plumbing contractor.

OK - just to be wise guy - are the cubic feet bigger or smaller in California ?

- The "energy content in BTU's varies. Here the factor is 1100 per CF for natural gas. Tank gas or Propane is more so different calcs are used. Also why it's a big problem to run a natural gas appliance on propane if not properly re-jetted.

Originally Posted by Dwight Doane

OK - just to be wise guy - are the cubic feet bigger or smaller in California ?

The BTU content of a CF of natural gas varies depending on temperature and pressure, which in turn varies by location. A 100,000 BTU/hr appliance may require 91 CFM in So Cal but 97 CFM elsewhere.

Bill,

" shut-off required ahead of the connector" (to an appliance). IRC 2422.1.2.4 UPC 1212.4

My take on your furnace pics is: In your case this means the shut-off comes before the CSST, at the tee, otherwise one could not disconnect the app without shutting off at the meter. Is that tee accessible?
However, Mfr's Instructions are req'd for permission to use CSST ( IRC 2422.1 UPC 1212.1 ) and must, of course, be followed ref. installation of the app.

As regards the fireplace app:

Connectors entirely in the same room as the Appliance. IRC 2422.1 UPC 1212.1
No connectors thro wall, floor, ceiling, or appl housing except ... IRC 2422.1.2.3 UPC 1212.1
... OK thro fireplaces w/factory installed protective grommet - PMI's. IRC 2422.1.2.3X

Shut-offs are req'd within 6ft, and in the same room as an appl. and be readily accessible.
Shut-offs are code within a decorative fireplace - PMI's, but forbidden in solid fuel burning fireplaces.

And don't forget to look for evidence that the gas line is bonded to a ground source when CSST is used.

All piping must be properly sized for every attached appliance under full house load-period.

Every gas appliance requires its own separate approved shutoff. Shutoffs must be within 6 feet of the appliance upstream of the union------------except for vented decorative appliances, room heaters and decorative appliances for installation in vented fireplaces shall be permitted to have the shutoff remote of the appliance as long as : it serves only that appliance, is labeled, and is "readily accessible".

CSST is approved for penetrating an appliance cabinet but it must be protected by a grommet and electrically insulated from the metal outerwrap of the fireplace. I know of no code prohibition for coming off the sediment trap per se as long as each appliance still has its own approved shutoff, union and are sized properly. CSST must meet the bonding requirements of the listing which is generally a #6 solid cu wire from the CSST brass coupling using a listed bonding clamp all the way back to the ECG in the distribution panel.

Shutoffs listed to ANSI Z21.15 are approved for use inside a woodburning fireplace for a gas logset as long as the shutoff is "accessible" and not directly affected by the heat. Remember, the appliance gas valve is only rated for 175F and they are much more sensitive than any shutoff. If you have a gas log lighter pipe, it cannot have a shutoff inside the firebox where wood is burned. If gas logs were installed but they were subsequently removed and the fireplace reverted back to woodburning, the shutoff inside the firebox should be removed and the gas pipe capped and shutoff where it connects to the branch piping or disconnected there. It must be remote of the fireplace but within 6ft. and is considered a throttling valve. A separate "shutoff" needs to be upstream of such a key valve. The gas pipe penetration into a firebox must be sealed. In a factory built fireplace, this means it must penetrate only boxes with a designated gas knockout and conduit--no drilling through the floor, pack around the pipe with rockwool insulation, then grout to the refractory panel with high temperature cement. Also note various mfrs. state a clearance to combustibles off the 1/2" NPT pipe once it exits the side of the fireplace into the chase cavity. CSST can NOT be connected directly through the knockout to a log lighter but it can be connected directly to a gas log set.
HTH

The way I see it... Is an appliance rated for 100000btus per hour will take 100000 buts of natural gas per hour... Not 91... Using the btu rating in my location 1 cuft is 1000 btu (natural gas) so in one hour that appliance will use 100 cubic feat ... Or 100000 btu of gas... The fact you get only 91 btu of usable heat due to other factors ( efficiency rating ) is different... The question/ answer would be if the input is 100mbh per hour and the appliance is 91% efficient... How long would it tAke to get 100 btu usable heat..? Which is a neat calculation . As for gas line sizing: take all known btu's plus future considerations ... Take total developed length and the. Look at the charts.... Gas line can start off large and drop down in size as btu's are dropped... But the total length colum stays the same.clear as mud??

- - - Updated - - -

The way I see it... Is an appliance rated for 100000btus per hour will take 100000 buts of natural gas per hour... Not 91... Using the btu rating in my location 1 cuft is 1000 btu (natural gas) so in one hour that appliance will use 100 cubic feat ... Or 100000 btu of gas... The fact you get only 91 btu of usable heat due to other factors ( efficiency rating ) is different... The question/ answer would be if the input is 100mbh per hour and the appliance is 91% efficient... How long would it tAke to get 100 btu usable heat..? Which is a neat calculation . As for gas line sizing: take all known btu's plus future considerations ... Take total developed length and the. Look at the charts.... Gas line can start off large and drop down in size as btu's are dropped... But the total length colum stays the same.clear as mud??

- - - Updated - - -

The way I see it... Is an appliance rated for 100000btus per hour will take 100000 buts of natural gas per hour... Not 91... Using the btu rating in my location 1 cuft is 1000 btu (natural gas) so in one hour that appliance will use 100 cubic feat ... Or 100000 btu of gas... The fact you get only 91 btu of usable heat due to other factors ( efficiency rating ) is different... The question/ answer would be if the input is 100mbh per hour and the appliance is 91% efficient... How long would it tAke to get 100 btu usable heat..? Which is a neat calculation . As for gas line sizing: take all known btu's plus future considerations ... Take total developed length and the. Look at the charts.... Gas line can start off large and drop down in size as btu's are dropped... But the total length colum stays the same.clear as mud??

- - - Updated - - -

The way I see it... Is an appliance rated for 100000btus per hour will take 100000 buts of natural gas per hour... Not 91... Using the btu rating in my location 1 cuft is 1000 btu (natural gas) so in one hour that appliance will use 100 cubic feat ... Or 100000 btu of gas... The fact you get only 91 btu of usable heat due to other factors ( efficiency rating ) is different... The question/ answer would be if the input is 100mbh per hour and the appliance is 91% efficient... How long would it tAke to get 100 btu usable heat..? Which is a neat calculation . As for gas line sizing: take all known btu's plus future considerations ... Take total developed length and the. Look at the charts.... Gas line can start off large and drop down in size as btu's are dropped... But the total length colum stays the same.clear as mud??

Originally Posted by c francis

The way I see it... Is an appliance rated for 100000btus per hour will take 100000 buts of natural gas per hour... Not 91...

The way you see it is mistaken. The difference is not about appliance efficiency, it's about energy density which is not constant for natural gas.

Francis welcome. I see you have a problem with quadruple posting. There is an edit function which allows you to make changes once you post.

The entire gas supply train: meter, regulators, piping, valves etc. provide FLOW--not BTU's. You could swap gases and flow nearly( not exactly) the same quantity of gas. It is the make up of what you are flowing that is being discussed. Not all "natural gas" is the same, which is why it is usually stated in terms of its Specific Gravity, which is a whole another discussion since we really should be talking vapor density. Back on topic: The heavier the Sp.Gr. the higher the BTU content and the lower the grade of the fuel. For instance, NG with a Sp. Gr. of 0.64 is heavier than pure methane, which is about 0.60 . Therefore, it has a blend of heavier hydrocarbons meaning a higher BTU rating per unit volume. There are correction factors to adjust orifices for varying Sp. Gr.s of fuels. The manifold gas pressure and air shutters often have to be adjusted and possibly a barometric damper if installed. On LPG, it gets worse because it starts off with a heavier BTU content per molecule then is blended with even heavier gases. Propane requires about 2.5x more air than NG per unit volume. This sometimes results in sooting and wasted fuel as it gets harder and harder to mix and burn the fuel completely. Now, NG fuel content tends to run a little more consistent except during peak loads when utilities spike the gas with whatever is lying around on the shelf: propane, iso-butane, LNG--whatever is available to meet the demand. Fortunately, these incursions seldom last long. If they did run longer, problems might manifest in certain equipment from burning hotter and dirtier. The AHRI conducted tests and is satisfied small spikes or "peak shaving" does not represent a major hazard to equipment or occupants. They say...

If you know your local NG is less than 1,000 BTUs per cubic foot then this should be baked into the sizing and set up of all attached combustion appliances.

As for sizing using the Longest Run Method--you stay in the row for that total Longest run then drop to the column with the BTUs for that section up to that point and that tells you the gas pipe for that segment. Note that this method factors in a Worst Case with all appliances firing.

HTH