Match Lit – good/bad

The most common method of igniting a fire pit is to flick the grill lighter and turn on the gas. Whoosh! Flame. There are a couple of concerns of which you should be aware. First and foremost, there is no failsafe for a match lit gas fire pit and should always be attended. If the flame goes out gas will continue to flow through the burner. When the gas finally finds a proper ignition source, the whole neighborhood will suddenly know about a problem at your house. I recommend against using the match lit method for public use, such as hotels, spas, golf courses, etc because of liability issues. (More about electronic ignition systems, private and public use, later.)

The other concern is with larger burners. There is no problem that I am aware of lighting a 24” or smaller fire ring; but I wonder about lighting a 30” or larger burner. The 30” burner may have a 150k or 300k BTU supply. Fire rings larger than 30 inches (36, 42, and 48 inches) will certainly have 300k BTU or more gas supplies. That might make for a different WHOOSH. As explained in the very first blog entry, the larger the burner ring, the shorter the flame. That is because the gas is spread over a wider area. When the valve is opened, gas is fed to the hub and passed outward to the rim with holes in the piping along the way. What is it like to ignite that much gas from one place on the outer ring? Please let me know if you have match lit one of these larger rings. Did you reach in with a lighter or did you stand back and toss a torch? How did/do you get your fire pit lit?

Next blog – Electronic ignition systems

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?