BTUs (British Thermal Units), in fire pit terms could mean the heat value of a fire pit fuel, propane gas, natural gas, wood logs etc. The greater the BTUs, assuming all other factors are constant, the greater the flames. There are many variables that will determine the flame height in a fire pit for example the fire pit design fittings such the fire pit burner/ring, hose length and gas pressure.
Fire pit burners come with a BTU rating which in this case is how much fuel a burner is going to consume to provide a reasonable flame height and heat. This rating will in knowing the gas pressure required in the gas burner for it to operate at its maximum.
The pressure of gas at the source and the distance the gas has to travel from the source to the fire pit burner will determine the flame height. The further away the hose is from the location of your fire pit, the weaker and smaller the flames may be and vice versa. Also, the number ‘corners’ the gas has to cut in the gas lines in order to finally reach the burner will also have an effect on the final gas pressure.
Choosing the appropriate fire pit burner for the gas pressure available to you at the source will ensure you get good flame height.
Fire ring size
When it comes to the flame height in relation to fire ring size, the gas orifice/ valve size must be considered.
A smaller ring size means greater flame height if the valve is kept at the same size. A larger ring will broaden the flame thereby reducing the flame height so to increase the flame height you will need an even larger gas orifice/valve.
Amount of air mixing with the gas
The amount of air that mixes with the gas before it is burns affects the height of the flame with all other factors constant. The more the air mixing with the gas, the taller the flames. Air is added or reduced by controlling the air shutter at the orifice.
Clean Gas Pipes
If you have a gas fire pit that used to have a reasonable flame height initially but currently the flames are not so pleasing, the issue could be gas pipes are clogged, nothing a little maintenance could not fix. Clean to remove corrosion and dirt which will improve and restore the flames to their original height.