Propane characteristics and cautions

Liquid propane (LP) is an excellent gas to fire your pit. Propane is trickier and more complex to handle than natural gas. Liquid propane is just that a liquid with a low boiling point. Liquid propane comes in different sized tanks. The tank is not completely filled. This is to allow the liquid propane room to boil off into gas. Larger tanks are able to boil off more liquid propane into gas and can, therefore, flow more propane gas. This is important to know when selecting the fire ring size for your pit. If the control valve flows more gas than the tank can process the tank will shut down to about 10% flow.

My thanks to Propane 101. Check out this website for much more information about propane.


SPECIAL ANNOUNCEMENT

I just heard last week of a propane fueled fire pit blowing up. Fire glass, the fire ring, and the pan were ejected out the top of the fire pit. Luckily, no one was injured. I have not heard of this happening before, but that is not to say it hasn't. As mentioned earlier, propane is heavier than natural gas. Somehow propane gas seeped down into the bottom of the pit and then ignited. It seems to me that the gas would have had to flow for a longer time than it normally takes to ignite the burner. Another possibility is that liquid propane got into the supply hose somehow. This condition will produce much more propane gas than what is produced in the tank. Now, this is only speculation on my part, but it does emphasize the fact that LP must be treated with caution and respect.

I would like to see your comments and experiences with fire pits, NG or LP, that have ignited in an uncommon way.

One other item, LP tends to cause soot as it burns. It is just not as clean burning as natural gas. An LP orifice added to the line to the burner introduces more air to the mixture going to the fire ring and helps to minimize this problem.

Next blog: Beautiful fire pit - Disappointing flame

Gas - NG or LP and how much?

Now that you understand what to expect from different sizes of fire rings, the next thing to consider is that which makes a burning ring something to behold, the gas. Gas fire pits are fueled by natural gas NG or liquid propane LP. The available gas determines the quality of the burner flame. Imagine putting time and money into a beautiful fire pit of your own design. You light it and it produces a 1 inch flame. What the hell happened?

Natural gas and liquid propane have their unique problems when applied to a fire pit. First of all for both, gas pressure rolls off over distance. Tapping into an existing smaller pipe with a larger pipe will not increase pressure. I strongly recommend using the services of a qualified plumber to assist in determining how to pipe the gas to the pit, and how much gas (in BTUs) to expect at that point. Someone qualified to measure gas pressure at the fire pit will save you much disappointment and expense later.

Let's start with natural gas for more detail. The most convenient source of natural gas for your home fire pit is the nearest line in the house. The problem with that is you are stuck with whatever pressure there is in that pipe. The architect may have designed the gas capacity to the house based on the expected usage. For instance, the architect may have sized the supply pipe from the meter to support the furnace, the water heater, and the kitchen stove. As I mentioned before, 150,000 BTU is an excellent pressure level for 18" and 24" fire rings. You may find there is considerably less in the pipe you plan to tap into. If you find that is indeed the case, the resolution is to run a line from the gas meter directly to the pit. Your plumber should be able to to select a pipe size that will deliver the quantity of gas necessary to run the pit for the desired burn.

Next post: "Let's talk propane"

Where to start when designing a gas fire pit

Build a fire pit (firepit)

It is my experience that many people building gas (natural gas NG or liquid propane LP) fire pits start at the end of the process and work backwards and are often disappointed with the results. Fire pit design must start with the fire ring (the burner). The final size and height of the pit depends on the proper selection of this one component. Fire rings generally come in 6 inch increments starting at 6 inches up to 48 inches. Burners are custom made above 48 inches. The rings are made of either black iron or stainless steel. Black iron is more susceptible to corrosion than stainless steel, but should still be serviceable for 2 to 4 years depending on the climate. Compare Seattle, Washington to Flagstaff, Arizona, for instance.

First Rule: The bigger the fire ring the shorter the flame at the same gas pressure. An 18 inch ring will have a 22-24 inch flame at 150,000 BTU at the pit. A 24 inch ring will produce a flame about 18 inches tall at the same pressure.

The fire ring affects the design of the pit because of space and offset distance requirements. More about this later in a separate blog entry.

Next blog "Got gas?"