Simple Fire Pit hardware

A match lit fire pit (strike a match and turn on the gas) is pretty simple. Starting with the fire ring and working back to the gas supply, you will need a flex connector from the fire ring hub to the ball valve. Another flex connector from the valve to the gas supply stub or LP hose is all you need. Hard piping is an option rather than the flex connectors. Flex connectors are corrugated on the inside. High pressure gas passing over these corrugations can set up a harmonic and the connector may sing. Hard piping does not have this problem, but is much more time consuming and precise to set up. High capacity flex connectors are now out, but I have not heard enough about these as yet to put forth an evaluation.

There are two other hardware pieces you may want to consider. Propane gas does not burn as cleanly as natural gas. Propane produces soot during the burn process. An LP orifice added to the line to the fire ring is designed to add more air to the propane gas mixture. This helps the gas to burn more cleanly.

Thanks to Hearth Products Controls

The fire ring must be supported and a pan may be just what you need. The burner has to rest somewhere. Whatever else you want to add to the pit (ceramic logs, lava rock, fire glass) also needs support. There are two types of pans, the traditional bowl style and the flat pan. Both have a nipple in the center to connect the fire ring. The burner will set down inside the bowl style. You can then add the decorative items on and around the ring.

The flat pan is much cheaper, but lacks the containment ability of the bowl style. It is simply a flat, stainless steel (round or square) piece with a nipple in the center to mount the fire ring.

Photos courtesy of Fire Pit Outfitter.com

These components are 1/2" connections. Larger fire rings like the 36" and above are available in 3/4" sizes. Rings of this size require a much higher gas pressure to get a decent sized flame, 300k BTU and more.

Next blog: A cool fire pit building system

Let's build a basic gas fire pit

42" x 18" match lit fire pit

Where do you start? The fire ring! Good for you. You have already decided on the burner size. That will have a bearing on the pit diameter. Most of the fire pits I have seen are octagon shaped, but square ones, rectangles, and even straight line shapes are common. Take the one above, for instance. The 42 inches is measured flat side to flat side.

There are a couple of things to consider when sizing the pit. Allow at least 4 horizontal inches between the fire ring and the capstones. This will prevent the heat from the flame from discoloring the capstones. If the flame is too close it can even cause the capstones to crack. Translated, that means that for a 24" ring the inner diameter of the capstone opening should be at least 32 inches. The ring should, also, set about four inches below the top edge of the pit to protect the flame from wind.

The pit height depends on taste. Do you see your guests propping their feet on this or maybe leaning on it and placing a cold one on the edge? You might want to consider a larger pit if this will happen while the fire pit is burning. There is nothing wrong with increasing the distance between the burner and the edges of the pit. Height can be excessive, though when sizing the fire pit. There is a point where the fire pit begins to look like a smokestack. That is not all that attractive to me. Again, selecting the height of you fire pit is strictly up to what appeals to you.

Next blog: The hardware

Beautiful fire pit - Disappointing flame

24" stainless steel fire ring

I got a call from a California contractor today. He built a beautiful fire pit, but the client was disappointed with the project. The match lit fire pit uses a 30" fire ring fueled by natural gas, NG. The lighting ceremony produced a 6" flame. The natural gas is delivered to the pit through a one inch pipe. Why is it so wimpy?

"Is there something wrong with the equipment?" he asked.

Unless there is a crimp in the line to the fire ring, restricting gas flow, this is not an equipment problem. The problem is more likely to be a lower than expected gas pressure at the fire pit. Resolving this problem will not be cheap.

The very first decision in fire pit design is 'what will the flame look like?' Once you have that, then the problem of delivering the necessary gas pressure must be solved. Two very important variables must be considered, where will the supply pipe tap be and how long is the run from there to the pit. Once you tap into an existing gas line you cannot create more pressure than is already there. The second consideration is the length of pipe from the supply to the pit. Gas pressure rolls off over distance (see blog of 10/21/8 for more detail).

I suggested to the contractor that he get a qualified plumber to measure the NG pressure at the pit. Pressure of 150k to the ring should produce about a 14 inch flame. That would give a starting point. Since the pit is already built, going to a smaller ring (the smaller the flame the higher the flame) is probably not a viable option.

If he tapped off from the house, he may have move it and tap off from the gas meter instead if the meter is close enough. If he has tapped from the meter, he will have to resize the pipe to the pit. That is an ugly option if the pipe is embedded in the patio cement.

Always, always start with the fire ring (the burner) before anything else. What should it look like? How will the proper amount of gas be delivered to accomplish that look?

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?"