Gas Line Sizing


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Old 11-09-07, 05:11 PM
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Gas Line Sizing

I currently have a 2 PSIG 1/2" natural gas line coming into the house, the line is copper tubing and is about 35' long from the meter to the furnace which is a high efficient furnace.

I'd like to add a 50 gallon water heater in the next year and a medium sized gas fireplace in the next 5 years and possibly switch to a gas cook top/electric oven combo in that same time frame.

The WH would be ~5' from the furnace, the FP would be ~20' from the furnace and the stove would be about 15' from the furnace.

Assuming my existing gas line is to small how do I calculate the size needed to accomodate all of the new appliances?

Thanks!
 
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Old 11-09-07, 07:23 PM
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There are a couple of ways to figure this.

You need to know the BTU loadings before hand. Draw a diagram with measurements of lengths. You need to find a gas chart, and these are online so search for them. BE SURE YOU USE THE RIGHT PRESSURE CHART FOR NATURAL GAS.

Start at the furthest appliance and the BTU load.This chart will tell you the size of pipe you need for that run.

Then you go the next furthest appliance see the pipe size for it. Add the BTU loads together and this is the new pipe size needed from where this tee's off the main, back to the meter.

Go the the third furthest and see what size pipe you need from the main. Add all 3 BTU loads together and see what pipe size you need from this tee back to the meter.

Work back towards the meter. Fittings (elbows, etc) have a friction loss equal to pipe length. You need to know how many twists and turns you are running. Fewer is very better. Do not use bushings for pipe reducers, these are illegal fittings. Check your code about using copper pipe, it may have to be put back in with black iron pipe.

Normally, I wouldn't mention how to do this. You caught me on a good night and you asked some decent questions.

Check with your insurance agent about do this work before you start. They may want you to have this done by a plumber/gasfitter/pipefitter instead of the home owner. Do get a permit regardless, this way you know it is done right.

Good luck with your project, more questions, ask in this thread and someone will answer you...
 
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Old 11-09-07, 08:29 PM
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Here's a link for reference but follow the advice of notuboo.

Gas Line Sizing
 
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Old 11-10-07, 04:44 AM
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Thanks

Thanks both of you for the information and link.

I sure hope copper is code here otherwise the builder and inspector didn't do to well with the house being 3 years old.

I'm pretty sure I'll have a professional redo the piping if needed but I want to know enough about it so they don't just install enough capacity for the furnace and WH and I end up having to redo it again for a fireplace.

I'll do some research on BTU loads of the appliances and see what I come up with. If I have questions I'll ask again.

Thanks again!
 
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Old 11-10-07, 05:16 AM
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Do your self a favor, ditch the copper tubing all together and run a 1 inch iron pipe main. It may be oversized on the charts but bigger isn't bad.
 
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Old 11-10-07, 08:22 AM
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Wink Gas Line

"I'm pretty sure I'll have a professional redo the piping if needed but I want to know enough about it so they don't just install enough capacity for the furnace and WH and I end up having to redo it again for a fireplace."

You must tell the pro. that you want extra capacity for future hook-ups, otherwise you can't blame them when it dosen't work, luck.
 
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Old 11-11-07, 05:50 AM
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Here's what I've come up with so far - the link was very helpful, their example was close to my needs.

Fireplace - 42K BTU 85' + 11 bends or fittings from meter
Stove - 75K BTU 75' + 10 b or f's from meter
Water Heater - 50K BTU 70' + 10 b or f's from meter
Furnace 138K BTU 55' 7 b or f's from meter

With my layout it would make the most sense to run the main line to the furnace then run 3 branches out from there.

I thought I saw somewhere each bend or fitting should be added as 1' to the distance wether I use the 90' or 100' total lenght the end result came out the same.

Total load is 295 BTU, Total distance is 96' (assuming bends count).

So to the Furnace I need 1 1/4" pipe
Furnace to FP is 1/2"
Furnace to Stove is 3/4"
Furncase to HW is 1/2"

Someone mentioned converting to iron pipe. What's the benefit of that over copper or CSST?

Thanks!
Greg
 
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Old 11-11-07, 08:06 AM
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Smile Gas Line

...."Someone mentioned converting to iron pipe. What's the benefit of that over copper or CSST?"....

I guess you haven't found out if copper is legal in your area?

Copper is probably the most expensive, a lot of areas require copper gas lines to be flared, no compression or SOLDER joints, this is a code question!

Iron pipe is the most economical it's allowed almost everywhere. If you don't want to do iron, I would go for CSST.

I don't like copper on gas because it's too easy to be damaged, up to you, have a good one.
 
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Old 11-11-07, 09:21 AM
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2 Psig

Thanks for the input on iron vs copper vs CSST.

I've seen enough cooper lines used in new homes here that for initial planning I am assuming it meets code otherwise a lot of buildings are ignoring code and the home inspectors aren't caring - I'll verify that when it comes time to do the work.

After more digging I'm wondering if my initial calculations are right - I've seen charts that reference low pressure gas and I just found a chart for 2 PSIG gas which I have coming into the house and stubbed out beside the furnace and then there is a regulator between that and the furnace.

On the 2PSIG chart it appears the 1/2" pipe should be good for 430K BTU at 100' which more than covers my needs.

Thanks for any input on 2PSIG vs low pressure you can offer!

My weekend switch from an electric to gas water heater is turning into quite the chore. If my existing gas line is enough at 2PSIG then I can hire someone to do the switch if I have to replumb all my gas lines then I'll have to wait and save more.
Thanks!
 
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Old 11-12-07, 06:01 PM
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2 psi gas past the meter is unusual. Most downstream gas pressures are less than 1/2 psi.

The gas regulating valve on most appliances (water heater, furnace etc.) are rated for a maximum inlet pressure of 1/2 psi so if you have 2 psi you will need additional regulators before any appliance.
 
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Old 11-13-07, 03:54 AM
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Thanks again...

Thanks, I wandered a few open houses on Sunday and 2 PSI gas seems to be pretty standard here and then they have a regulator after that. Based on the 2 PSI chart I fould it looks like I have enough capacity so i won't have to redo the entire system just add new.

Now it's time to start talking to the local plumbing pros and see who offers what for water heaters.

Thanks everyone.
 
 

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