You have a tank containing fuel, another device (furnace) that requires fuel and air, and the pipe connecting the two of them. If all your appliances is running simultaneously, there must be enough airflow and steady gas pressure for everything to operate correctly. When size is wrong, it creates soot build-up and short flames. This can cause appliances to fail during critical times. This is one problem most homeowners don’t consider.
This is the chart. I matched it up with pipe diameter. Run length vs. It shows the BTU capacity. And this is the thing: it meets NFPA standard for liquid propane pressure drop.
How to Choose the Right Propane Pipe Size
What do you do? You measure out how far from your tank each appliance is (furthest to nearest). Look down the left column until you hit number matching that row. Now you pick a pipe size which provide for total BTU needs of all the devices along that run. Furnace + water heater + generator = add them all together. Make sure the pipe are large enough to deliver that amount without starving any one device. That’s basic plumbing logic applied to high energy fuel.
What happens on a long run, like a hundred feet? At such a length, a half-inch pipe can’t carry much of a load; the friction in a small tube use up too much pressure by the time it gets to the burner. You think you’ll save some bucks if you downsize the line, but that’s false economy. Your appliance will perform inefficiently, creating less heat while producing higher levels of carbon monoxide. Be smarter: Upsize your pipe now, or be prepared to pay a service tech later when he diagnose combustion problems. As the chart shows, longer runs mean much lower capacity. So the longest part of your run is often also most important part.
The specifics of propane are different than, and those details affect the math. First, propane weighs more then air, which causes it to settle instead of floating upward, meaning that ventilation inside is critical if there’s any possibility of leaks. Second, because propane is more energy-dense, it will provide same amount of heat with fewer BTUs. But you must have sufficient volume to hold pressure. According to the infographic, while natural gas produces around a thousand BTUs per cubic foot, propane produces about 2,500. When calculating flow rates, that density play into the equation.
The math is part of the story, but so are installation details. Most indoor and outdoor runs will need to be on black iron pipe, which should also be secured at intervals of no more than four feet. Vibration cause fittings to loosen with time. Loose fittings leak. The fittings should also be connected using yellow PTFE tape (specifically rated for gas). White tape is not rated for either the chemical composition or pressure of propane and can fail or degrade without being noticed. No test…no pass. After you cap off the lines and attach them together, put pressure on it and run soapy water around all the joints. Look for bubbles. Bubbles mean no bueno. Hold it under pressure for 15 minutes just to be sure everything has set. Don’t try to cut corners on this to save some time. An hour’s worth of work isn’t as bad as an emergency call in the middle of a cold snap or storm if you discover a leak.
Codes differ by region so professional advice is always good. Making a mistake could of cost you.
Propane piping isn’t rocket science, it’s accurate engineering. Consider your entire house as one complete system, not an assortment of standalone appliances. Apply the physics of gas flow and use existing reference information to size your propane pipe so that in cold weather, your heating system will work propery. We want consistent, even heat without any worries. Properly sized propane pipe flow results in a warm house for you … and you staying out of the cold.
