In the basement, you’ve installed a new high-efficiency furnace. It’s ready to run, says the installer, and he hands you the bill.
Back in the kitchen, you flip the switch to ignite your gas range. Sput. Sput. The burners sounds like they’re wheezing their last breath. But the flame? The flame dances franticly, then rises off the burner head as if repelled by an invisible magnet. No matter what you do, it won’t settle down.
Why Your Gas Pipe Size Matters
Such a failure isn’t usualy a problem with the appliance itself. It’s almost always a problem with the pipe it feeds from.
Most of us imagine that gas rushes into our house through any hole we put in the wall. Wrong again. Like air flowing through a narrow straw, gas acts more like a liquid, and if the straw is too long (or too narrow) the pressure drop before reaching its destination. One appliance may hum while another starve for fuel, such as your water heater. This can cause all sorts of nasty combustion problems that no amount of tweaking the thermostat will cure.
This means that a half-inch line works fine for a short ten-foot run to your oven, but you can’t push three hundred thousand BTUs through it more than fifty feet either. The above chart matches run length with both pipe diameter and BTU demand. You have to think about the entire system as a network of connections rather then each connection by itself.
Often folks will size the line to fit their first appliance and hope no one notice the deficit for the rest of the house. Add up the total load of your furnace, water heater, dryer, and fireplace and you might find you need an inch for your main instead of three quarters. This maintains stable pressure when everything are running at once.
Diameter isn’t everything; material selection counts, too. For indoor residential projects, black iron pipe is the norm. It is strong enough to handle both physical abuse and thermal expansion, yet it won’t crack or fail under these conditions. While it’s heavy and requires threading, get it right and it will last forever.
If you’re retrofitting, corrugated stainless steel tubing bends easily around obstacles so no more series of elbows. Less fittings = fewer turbulent spots within the line. Turbulence equals pressure drop which equals that sputtering burner dilemma.
And don’t forget about equivalent lengths of fittings: Each 90-degree elbow you add equates to approximately an additional foot-and-a-half of linear resistance in the line. All those corners in your basement could translate to a twenty-foot run becoming a forty-foot effective length on paper.
Special mention goes to those who run on propane; liquid propane has a different specific gravity than natural gas. Denser. Heavier. That means that it will fill out your pipe differently. And pressure will drop at different rates the further it travel down the line. Propane systems has slightly altered sizing rules, something you’ll want to pay close attention to in order to get enough flow. No, you cannot just change fuels and leave the pipe sizes alone.
Safety regs aren’t something to mess around with. Each joint needs to be properly sealed with a gas-rated dope or tape. Avoid regular Teflon tape because it will degrade when exposed to hydrocarbons. With a soapy water leak check, you’ll see bubbles form when the gas finds its way out, until you turn it on and then off again. Tedious? Yes. It is the only way to ensure a leakproof system.
DIYers hate pulling permits and getting inspectors out. Inspectors will check that appliance drip legs are properly installed to prevent sediment from building up and clogging valves over time. Shutoff valves must be accessible; in case of emergency, you need to shut down fuel fast. The inspector checks and gives their sign-off that it all pass a series of real-world stress tests.
Now you can go home confident your home is warm and safe … no need to worry if that little hiss means something or not. A proper size means a steady blue flame. You won’t have to worry about air quality or comfort levels when the coldest night of the year rolls around. Every minute spent planning should of been worth it.
