How much gas line do I need? House natural gas content

My house has gas (heheh)

Currently the only thing that is NG powered is the forced air heating, but I want to add some pipe to pop up into the kitchen for a gas range, and possibly drop a pipe below it for a gas water heater when my electric tank dies (looks like any day now).

It's a teeny house, and it appears that it enters the house as 3/4", goes across the basement ceiling as 3/4", then necks down to 1/2 before going in the furnace.  3/4" seems small to supply enough for adding two more gas appliances.  How do I calculate if I have enough flow to supply things?  How much more would I need for a tankless gas water heater?

Contact your supplier.

Contact your supplier.

 there might even be some reg,s concerning do  it yourself gas lines.

 some states are really touchy

DIY work may be allowed, but it can depend more on the local authority than any specific state rules.  The work may need to be inspected and signed off.   I ran a lot of gas line at my ex's house and it passed inspection, but the line from the regulator was a 2" line, so there was more to work with. 

Here in PA every municipality's permit requirements are different, but how will they know you did the change since you already have gas service?  My place is gas everything, and each unit has a 3/4 connection at the inlet. The line in from the street is only 1.5. I am heating 6 large rooms and a full basement with hot air. When they re piped my street last year the main is only 3 inch pex, they ran it through the old leaky iron! Just remember to leak check everything with soapy water before you light any fires!

A 3/4” line can handle 2 1/2 times the volume of a 1/2” line. A 3” line is huge. 

Line size and capacity changes dramatically before and after the regulator.

I was once woken from a sound sleep by the sound of a house blowing itself entirely to toothpicks, eight blocks away from me.  I thought someone had driven into my house.

He had done his own gas fitting.

Gas pipe sizing is dependent on gas pressure, gas load or demand, and the distance you are trying to get it to go.  Elbows in the pipe add distance.  Google gas pipe sizing chart and take your pick.  You need the chart that is based on 1/2psi, and make sure you are reading a chart for nautural gas and not propane.  Then get the BTU ratings on the appliances.  Then measure how long each branch needs to be.  Anybody with half a brain and some mechanical aptitude can size gas pipe once they spend a few minutes looking at the examples provided with the charts.  Installing it according to code is another thing thou.  I'm guessing 1" coming in until the first branch, then you can drop to 3/4' to feed the second two appliances.  

Streetwiseguy said:

Line size and capacity changes dramatically before and after the regulator.

I was once woken from a sound sleep by the sound of a house blowing itself entirely to toothpicks, eight blocks away from me.  I thought someone had driven into my house.

He had done his own gas fitting.

Did he make his own meth too? 

I agree with most everything so far. However, Just find the chart and read it. 

While the line sizes and pressures and volumes and gas properties and stuff all matter to the engineering problem, the charts have already done the engineering.

TurnerX19 said:

Here in PA every municipality's permit requirements are different, but how will they know you did the change since you already have gas service?  My place is gas everything, and each unit has a 3/4 connection at the inlet. The line in from the street is only 1.5. I am heating 6 large rooms and a full basement with hot air. When they re piped my street last year the main is only 3 inch pex, they ran it through the old leaky iron! Just remember to leak check everything with soapy water before you light any fires!

This was my thought.  For the most part here in my municipality, there is nothing about permitting what appliances are gas or electric.  The house has gas.  The house has electric.  The only person I need to impress is the home inspector of the future buyer if I ever sell the house.  I have done plenty of this before so I'm confident.  If I can flare my own brake lines to hold 2500 psi, I can thread some black pipe to hold less than 2 psi.

My township is pretty permissive.  I asked about getting a permit to expand my garage and they asked me how big.  I said doubling the size from 12x24 to 24x24.  He laughed and said I don't need a permit for free-standing buildings under 800 sf.  (of course there are setbacks and non-permeable rules)

tr8todd said:

Gas pipe sizing is dependent on gas pressure, gas load or demand, and the distance you are trying to get it to go.  Elbows in the pipe add distance.  Google gas pipe sizing chart and take your pick.  You need the chart that is based on 1/2psi, and make sure you are reading a chart for nautural gas and not propane.  Then get the BTU ratings on the appliances.  Then measure how long each branch needs to be.  Anybody with half a brain and some mechanical aptitude can size gas pipe once they spend a few minutes looking at the examples provided with the charts.  Installing it according to code is another thing thou.  I'm guessing 1" coming in until the first branch, then you can drop to 3/4' to feed the second two appliances.  

This is one of my confusions.  I did google things and I can look at charts of pipe size vs BTU or pipe size vs CFM.  My real shortcoming is... how do I size things based on actual useage?  I can add BTU + BTU, I just don't know WHAT to add.

For example, let's look at a typical gas range.  I can add the BTUs of the burners (around 50k) plus the oven (who knows), then add for an on-demand water heater (3gpm for a washer, 2 gpm for a shower, 1 gpm for a sink... suddenly I'm into 8 gpm total which is 200k BTU), plus furnace....

The thing is, I live alone, so the chances that I'll be using 5 burners and an oven while taking a shower and doing a hot load of whites while the furnace is running is slim.  But, I'm not doing it for just me.  This small house could easily support a small family of 4 with two kids.  This would dramatically change the demand.  I rarely have more than one burner going to cook a meal.  I rarely bake.  I almost never use hot water in the laundry.  I keep the heat set to 68.  That is different from a potential demand of two adults with germaphobia, one infant in diapers, and one adolescent kid who keeps setting the heat to 76.  Make sense?  I don't want to install all of this only to realize I've made it something I have to change before I sell (if I sell).

If I add up all the BTUs and demands possible, I'm looking at big numbers.  How do installers determine the actual average needs of gas flow?  Is there a calculation where; insert appliance BTUs + climate zone X + insulation R-value + number of people that could realistically live in the house = CFM?

Robbie said:

I agree with most everything so far. However, Just find the chart and read it. 

While the line sizes and pressures and volumes and gas properties and stuff all matter to the engineering problem, the charts have already done the engineering.

I have, but here's my confusion:

Right now it's just me in an 835 sf house.  I come home from work in the summer (no furnace operation) and I take a shower (1.5 GPM water which means 15,000 BTU) then I fire up the small burner on the stove to cook a grilled cheese (5000 BTU), then I do a load of particularly soiled whites and use hot water (2 GPM water or 20,000 BTU)  In this scenario, I'm using a max of 20k BTU at any given time.

Scenario #2:  I get a live-in SWMBO.  She bakes a lot, cooks every meal, showers twice a day, and it's winter so the furnace is running.

Scenario #3:  I'm having a party with 20 people and several of them wash their hands in hot water, it's 10 degrees outside and windy, I'm helping a friend by washing his shirt because he spilled red wine on it, and all 5 burners are cooking food and there is a casserole in the oven and the dishwasher is on cleaning the pots and pans I used yesterday.

Scenario #4:  I sell the house to a couple with two kids; one in diapers and the dad is a germaphobe who washes everything in hot water.  The mom is always cold so she keeps the stat set to 76 degrees.  Dad loves to grill, so he hooks up a monster gas grill to the outside line so he can cook up a few pounds of flesh for the family dinner while mom bakes a cake and makes potatoes, corn, and gravy on the stovetop.

These scenarios represent a BTU usage of anywhere from 20k up to nearly 400k.  Is there a metric to estimate what is actually a logical CFM supply based on what "should" be available for use?

In reply to Curtis :

You are WAAY over-thinking it. 

You size it for peak demand. Just as you would for electricity. 

You wouldn’t run 12 ga wire for your electric range because you only intend to use the front left burner.

...and you wouldn’t put a 1 gallon fuel tank in a car because you don’t intend to drive very far. 

I used to work for a gas connector manufacturer (https://www.watts.com/solutions/channel-solutions/residential) and what I recall is that improperly sized gas lines are a MAJOR safety hazard. You can get gas to an appliance and it will light, but without enough flow, it will not be burning correctly and could kill everyone in the house. CO2 IIRC.

First off, the meter on your house may not allow the total CFM you need, so you need to start there.  Many homes are close to or at their CFM limit already, so you can't just add more pipe. You have to upgrade the meter, the main line, and all of the branch lines. You definitely have to size for peak demand with everything on! The calculations are actually run from the end of the line, at the appliances, backwards. You increase pipe size as you go to come up with a main pipe diameter and a CFM for the meter.

Check out NFPA 54 for all the details and if you aren't 100% comfortable with the calculations, have a pro do it.

You don't size for anticipated demand.  You size for maximum total possible demand.  Add up everything on the little stickers.  Yes, if you want an on demand water heater, then figure 200,000btus.  Thats why adding an on demand to an old house is such a big deal.  Now once you have sized your pipes, go out and read the meter.  You need a meter that can deliver that much gas.  a 250K meter isn't going to work if you want to heat the house and take a shower at the same time.  Gas company will need to give you a bigger meter.  They will if there is a large enough pipe from the street to your meter, and there is sufficient gas pressure in your neighborhood to give you more gas.  Don't just assume your gas company is going to sell you more gas than you are already using.  Here, if we do anything that adds BTUs to a house, we have to have permission to do so before a gas permit is pulled.  I have seen HVAC guys swap out oil burners to new gas ones and then tell the homeowner to call a plumber to hook up the gas.  Call gas company and the answer is a flat no.  Then scramble to convert unit to propane which is just as expensive as oil, and get a propane company to install a tank.  I know of newer neighborhoods where the gas running into said neighborhood is insufficient.  Cold mornings, everybody gets up to go to work.  Furnaces kick on, on demand water heaters fire, not enough gas pressure to run these high tech appliances and they go into shut down.  Poor guys at end of the individual branches loose hot water almost every time they take a shower in the mornings.  Think of it like fuel line.  You have a nice 3/8" line in your Malibu.  Add a big block with a blower and nitrous.  Guess what ,fuel line isn't big enough, and you need a serious fuel pump.  Big block might idle just fine with what was in there, but you can't make a pass with it.  There is a demand factor that is calculated in for water pipe sizing, but not for gas pipe sizing.

Poke around and see what the Code is.  Sure, you can DIY minor surgery, but wouldn't the results be better with professional intervention?  If you're not totally comfortable, confident and certain of a positive outcome, don't berke with it.

That's just me....

Size based on maximum demand AFTER you insulate the house properly (R-19+ in the walls, R-53+ in the attic, double glazed windows in any room with a heating duct) and downsize the furnace appropriately.

How do you fit R19 in a 2x4 stud wall? (serious question!)

The mechanical part is easy.  I have run many gas lines in my life.  It's just the sizing that has me confused

SVreX said:

In reply to Curtis :

You are WAAY over-thinking it. 

You size it for peak demand. Just as you would for electricity. 

You wouldn’t run 12 ga wire for your electric range because you only intend to use the front left burner.

Meeee?  Overthink things????  You totally understand me.  I can't just ask for an answer, I have to understand how the molecules of natural gas react to the I.D. surface finish of black pipe biased against pressure and moisture content, and accounting for moon phase.  I don't think I know how to ask a yes or no question.  :)

This is exactly how I was approaching it AND THE SAME REASON IT'S CONFUSING ME.  For example... I have a 200A panel with 30 bays.  If I add up the possible amperage of all the circuits in my house, I get 440A, but it is sized so that the 200 is more than enough to supply the things I would use at one time.  If I just add up all the BTUs or CFMs I would need for all of these gas appliances based on their max effort, I would need a monster gas line.  Or to complete the analogy... if I added up all the capacities of the bays in my service panel, I would have to supply it with 500A service.  And yet, 200A is overkill for my tiny house with one person.

I get the anaolgy... 12 ga wire to use one burner... but the stove is on a double 50A with 2-ga wire.  Am I making sense?  I know that a single 3/4" will be enough to supply any ONE of my gas endeavors, just like my 200A service is enough to supply any ONE of my appliances.  The electric isn't sized to supply all possible amperage draws, it is designed to supply enough for some of them at one time.

I have found all the google charts for CFM and BTU per pipe size and pressure, and I've read up on temp deltas per GPM flow of tankless heaters.  I just don't know how to size the supply based on expected occupancy and demand.  You said "size it for peak demand."  How do I find peak demand?  In the case of my water service, it's 3/4" into the house and then it splits to 1/2" for everything else.  If I turn on every faucet and the dishwasher and washing machine, it is undersized... but who opens every faucet?  If I plug in a welder to every circuit in my house and pull the trigger, none of the individual breakers will trip, but the big 200A breaker will.

So how do I figure out how much CFM I will need based on the real-world demand of those appliances?

dculberson said:

How do you fit R19 in a 2x4 stud wall? (serious question!)

You don't.

And it's not required.  The IECC (International Energy Conservation Code) requires R-13 in climate zones 1-4 (south of the US beltline), and R-20 in zones 5 and 6.  Zones 7 and 8 require R-21 (that's like the very Northern edge of N. Dakota, and the Yukon).

Ceilings require R-30 in zones 1-3 (Southern states), R-38 in Zones 4 and 5 (up to about the Great Lakes).  Zones 6, 7, and 8 require R-49.

No where in the US requires R-53. Including the Northwest Artic.

In reply to Curtis :

Curtis said:

  If I add up the possible amperage of all the circuits in my house, I get 440A, but it is sized so that the 200 is more than enough to supply the things I would use at one time. 

I'm willing to bet you are wrong.

You don't add the BREAKERS.  You add the LOAD.  Just because you have a 20A circuit does not mean your vacuum cleaner uses 20A.  Go through your house, read the motor load plates on every device.  I guarantee you do not have 440A of load in that house.  Total of combined branch circuits can exceed the capacity of the main breaker, as long as the load does not.

But you are trying to de-rate the load.  If your furnace says it can burn 50,000 BTUs, that's how much you need to pipe for.  It's not a vacuum cleaner.

In reply to Curtis :

Peak demand is the maximum BTUs on all of the appliance data plates combined.  I know you don't want it to be that, but it is.

And yes, I understand your point.