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I’m converting some stoves in my house from LP to Nat Gas. The existing supply lines for LP are flexible 3/8 copper with compression fittings. As I understand it, Nat Gas works at lower pressure (5lbs vs 20 lbs???), so I think I’m OK with the integrity of the lines, but I hear about this interior scaleing when the gas meets copper. Some say this is only an issue if water is present in system (rare since your gas meter would freeze) or at high (over 200 Farenheit)operating temperatures. Anyone want to weigh in on this debate? At worst will I just have to clean the screens on the stove gas valves every once in a while? Thanks.
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Several issues here. Will it deliver enough gas, are the materials correct, and is it allowed?
"some stoves" is a little vague. How many ranges and/or cooktops? How long is the current 3/8" supply line? 50' of 3/8 pipe will allow about 60,000 BTU/hour of LP to flow at 11" water column pressure which is typical and 0.5" w.c. pressure drop which is a good goal. If 20' long the pipe will move about 100,000 BTU/hour of LP. Each stove burner is about 10,000 BTU/hour, the oven is a few times that. 65,000 would a reasonable guess PER RANGE. So currently, the LP in 3/8" looks good for ONE range. It probably works for more than one because you rarely operate all the burners on all the stoves at once.
If your natural gas is available at 2 psi and you can lose 1.5 psi to piping pressure drop, then 50' of 3/8 pipe would allow 240,000 BTU/hour to flow. Good for 4 ranges. But sometimes the gas company only gives you 7" water column = 0.25 psi. Then less BTU's of NG would flow than LP and it ain't going to work.)
Copper is allowed for fuel gas in some areas (type K tubing or tinned copper), but not in others. Check with your inspector, building department or gas company. Really. Check with them. I'm not kidding. The water company, sewer department and propane supplier may all have hooked up to your house once the inspector signed off. Or not even that, if you're outside the city limits. The gas company won't. They'll inspect your piping and insist it meet their standards which can be different from the city's. Maybe there's a cool and laid-back gas company somewhere in this country but the dozen or so I've dealt with from Fresno, CA to Anchorage, AK are a bunch of paternalistic pricks who fell they know better then you how you should plumb your house. (Okay, I'm done venting now.)
"Scale" is an issue in galvinized pipes if the sulphur in the fuel reacts with water to form sulphuric acid and erodes flakes of zinc which float downstream and clog your appliance jets and valves. The risk is they can clog a valve OPEN and then the water heater is a P&T away from blowing up. That's why a downward-facing dead leg is a good idea just before the appliance. In copper pipe you can get a black feathery soot from the sulphur which eventually clogs the pipe completely. Whether untreated (type K, not tinned) copper is allowed in your area may be based on the sulphur content of your provider's natural gas.
You can calculate exactly what pipe sizes are needed, but the following covers almost everything: 3/4" pipe main line with 1/2" lines to each appliance. 3/4" to the range if your local code requires it as some do.
All of the above is in Taunton's excellent book on "Plumbing a House" by Peter Hemp. Except for my ranting about gas companies. And I had to extrapolate down to 3/8" pipe because that miminal installation isn't covered in the charts he provides.
So 3/8" might carry enough BTU's if your gas supply is at a high enough pressure. Copper may or may not be allowed. 3/4" may be required to each range. Ask your gas company. They aren't shy about telling you what is required. -David
*Stray,David makes some good points. Copper is Ok for propane but not for natural gas is what I was taught.Compression fittings are not allowed, gotta use threaded or flares.Ask some plumbers here http://www.plbg.com/KK
*David,Some very good points. I hadn't considered the fact that 3/8 may not supply enough to fuel three stoves at once. It's a 4 unit apartment house, and the copper will be split off 1/2" black iron. One stove is 15' away from this juncture, and two more stoves are about 25' away on separate lines (the 4th stove is on the black iron feed, and has 1/2" to the stove). I will consult local utility, but wanted to get some practical advise before-hand too (noting, as you did, that utilities are not the last bastion of logical and reasonable rules...).I have heard that the sulphur content is not an issue any more due to deregulation and a need of the industry to provide more homogeneous product for wider distribution. The current additive for olfactory detection doesn't have the same corrosive effects that the sulphur did a decade or more ago. This is all hearsay mind you; from bar flies, and internet flies that I've chatted with lately....
*Yes, the mercaptans (sulphurous compounds similar to what skunks produce) are at a very low concentration and are not a corrisive concern. The 1/2" feeder line makes this sound a lot more workable. My Kenai gas company wouldn't connect me until I had one gas appliance ready to light. That is common. An approach that sometimes works is to get your most presentable appliance/piping ready for them to look at and hide the rest or leave them on LP for another month. -David
*David:Thank you for the interesting and informative posting.
*Wouldn't be Code in our neck of the woods. We do black cast iron pipe with pipe dope instead of teflon tape for the joints, and pressure test it. Must hold 50 lbs for 15 minutes. We use a bicycle guage and an air compressor for the air test.
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I'm converting some stoves in my house from LP to Nat Gas. The existing supply lines for LP are flexible 3/8 copper with compression fittings. As I understand it, Nat Gas works at lower pressure (5lbs vs 20 lbs???), so I think I'm OK with the integrity of the lines, but I hear about this interior scaleing when the gas meets copper. Some say this is only an issue if water is present in system (rare since your gas meter would freeze) or at high (over 200 Farenheit)operating temperatures. Anyone want to weigh in on this debate? At worst will I just have to clean the screens on the stove gas valves every once in a while? Thanks.