With the ever growing popularity of Lava Stones, Fire Rocks and Fire Balls being used in Fire Pits, and in particular the larger sizes, I was recently reminded whilst helping a client with an installation problem, how important it is to install these large size rocks correctly into your fire pit or fireplace.
How a Fire Pit Burner Works
It is a common and understandable misconception that a fire pit burner works in the same manner as a domestic gas hob burner, but in fact, that is not the case.
On an ordinary gas hob burner, the flame burns adjacent to where the gas exits the burner as is clearly shown in the image below.
However, a fire pit burner does not function this way.
In fact, it is probably incorrect to refer to this item as a burner. A Gas Delivery System might be more accurate because it is designed to deliver the gas, but the gas then percolates upwards through the fire glass/lava rock and it should not ignite until it more or less reaches the surface.
The important point here is that the flame does not burn adjacent to the burner, but rather a couple of inches directly above it.
As the gas percolates up through the fire pit media it also spreads out into a larger area, so when it finally ignites it has a larger footprint and therefore a better-looking fire.
To to maximize this 'spread' effect we need to slightly slow the upward progress of the gas. If you were to install large sized Fire Pit Rocks directly into your fire pit, the large gaps or cavities between the rock that would occur allow the gas to escape quickly, we need to slow it down a little.
When you turn on the gas and light your fire pit these cavities would fill with gas and ignite, which in itself is not a good thing. But these cavities may be much closer or even in contact with the burner, and thus when the gas is ignited you would have a hot spot, and the burner is not protected by a layer of fire media as it should be.
Depending on how your stones sit, you may not even be aware that these hot spots exist!
In these circumstances, the very best that may happen is that your burner will warp due to the excessive heat, and it may even burn holes into the burner, if the hot spot is close or in contact with it, rendering your burner unfit for purpose.
We need to create a 'protective' layer between the burner and the flame, which will allow the gas to pass through.
The easiest and most effective way to do this is to use a small size lava rock, we recommend 1/4 to 1/2" as a filler. This will slow the rise of the gas down a fraction but importantly not impede it too much.
The objective here is to bury the burner under this small sized lava rock until there is at least 1/2" of lava rock over the burner. ( Please note this is the recommendation for conventional style burners )
It is interesting to note that two of the leading manufacturers of burners in the US have slightly different recommendations on this matter. One recommends the 1/2" we have already mentioned the other says to fill only to be level with the top of the burner, but not burying the burner.
This 'filler' concept applies to both natural gas and Propane installations.
I can only say that we have always covered the burner with about 1/2" and found that to work extremely well.
Some people use Silica Sand as a filler, and this will work too, however, only fill up to the level of the burner, and ensure that no sand particles fall into the gas ports in the burner ring.
The same principle can also be used for fire glass, especially the larger sized variety.
Having installed your filler base you can then arrange your larger Lava Rocks or Stones on top.
American Fireglass have a great range of Fire Rocks and Fire Balls which are supplied complete with the appropriate quantity of lava rock and advise that the rocks must not be installed with the appropriate fire media base ( small lava rock ).
A few points of caution.
Be sure that your fire glass or lava rock does not prevent a Spark Ignition Probe from functioning. Some styles have a protective cage over them, but others are a simple probe and you need to ensure that nothing is getting between the spark ignitors probes and therefore inhibiting the spark.
If you have a Propane Fire Pit, Propane gas is heavier than air and so when it escapes from the burner its natural reaction is to flow down not upwards. If you are not happy with the flame check to see if you have covered the burner with too much filler. If that is the case try removing some and check if this improves the flame quality.