The Fire-Fountain

A waterfountain and fire pit hybrid

The finished product

The finished fire-fountain in Springville Utah The finished fire-fountain The finished fire-fountain at night

How It's Made

This cut-away view shows the hidden components of the fire-fountain.
  1. Gravel Base, 2 inches thick.
  2. Leveling Sand, 3/4 inch thick
  3. Water Pump, purchased from harbor freight has a flow capacity of 1300 gallons per hour (gph). The 1/6 hp motor is powered by 120V electricity, which is supplied by a direct burial cable run from the wall-mounted switch. Direct burial cable is a cheap option, but is more succeptable to damage from shovels than a conduit.
  4. Pond Reservoir. This reservoir catches and stores the water that is pumped into the fire bowl. The top of the reservoir is almost as wide as the stone brick walls in order to catch all the water falling and splashing from the fire bowl. The structure is made of 3/4" PVC pipe and wrapped with a thick pond liner. There are 8 sides to the circular shape and it tapers inward at the bottom.
  5. Fire Bowl. Water overflows from this bowl back into the pond reservoir. Natural gas is released in a circular pattern under the surface and bubbles to the top where it ignites.
  6. Rock Fill
  7. Rock Fill Screen. This screen is anchored into the surrounding stone blocks to support the weight of the rocks and small children/animals who may inadvertantly step on the rock fill. Kids tends to immediately jump on when the water is running!
  8. Stone Bricks. The bricks are tapered in from front to back, and this taper allows for the stone wall to be cleanly curved at a specific radius (unless your willing to cut each piece). These stones from Home Depot made a perfect circle with an acceptable diameter.

How the fire fountain works
This view shows the hidden components of the fire bowl
  1. Fire Bowl. To keep the cost of construction down, I opted to use a bowl made from resin. The obvious downside is that it has a very low melting point, and would never hold up without the water overflowing from the bowl. The upside is that it was less than $100 as compared with over $600 for a comprable bowl made of cement.
  2. Water Distribution. The water flow rate it too high to allow for just a 1" pipe to come straight into the fire bowl. The high velocity makes a bulge in the liquid surface and does not distribute water effectively. To reduce the velocity I split the flow 3 times using 3 PVC tees, now there is 4x the cross-sectional area of PVC pipe leading to a lower exit velocity. This distributes the water gently.
  3. Natural Gas Inlet. The natural gas flows in from the bottom of the bowl through 1/2" copper tubing. The tubing makes an arch above the water line for reasons described below.
  4. Natural Gas Tee. This tee sends the gas in two directions through the gas distributor.
  5. Gas Distribution Ring. 12 holes of 1/8" diameter are drilled into the bottom of this ring to send natural gas into the fire bowl. This ring is below the water level so the gas bubbles up to the surface where it is ignited.

Low Pressure Challenge

The natural gas supply I used was installed when my house was constructed. I asked the builder to run a line to the back wall of the house, which was tee'd off from the water heater. Natural gas is throttled down to very low pressures inside homes. This very low pressure cannot even lift 18 inches of water, so if I allowed the vertical section of tube feeding the gas distribution ring to flood, the water becomes and effective seal preventing gas from flowing. This is great for safety, but bad for function...

My first attempt to solve this problem was to use a check valve. However, no check valves I could find would work because the pressure drops across them were too high.

I then purchased a venturi vacuum pump that is used for cleaning fish tanks. It operates on the principle that flowing water, when expanded, can create a negative pressure. A properly shaped device can thus pull a strong vacuum with only water out of the hose. I tried placing the device on the pump discharge, but the water flow was too greatly restricted and had a very high discharge velocity.

The solution I used was a simple inverted U trap. The top crest of the trap has to be above the water surface (the top of the bowl) to prevent water from ever getting into the vertical tube. Water is able to flood the gas distribution ring, but is unable to rise up and over the inverted trap.
How the firefountain works with callouts shown
The copper tube feeding the fire ring must rise above the top of the water level.
To hide this tube I chose to bury it in the same rocks that fill the bowl.
Copper tube is hidden under pile of rocks. The yellow natural gas valve handle can be seen near the front of the basin.

Operating Procedures

  1. Turn On Water Pump
    The switch to turn on the fountain pump is fixed on the house near the power source (outlet on back wall). Note It is generally safer to keep a switch close to its power supply, so when the switch is off less wiring is energized. All the cable buried underground is after the switch, so it is only live when the pump is on. Power to the switch can be removed by unplugging the SEOW cable plugged into the outlet.

  2. Open 1st Natural Gas Valve.
    There are two valves feeding the fire fountain. One fixed to the house which cuts off the natural gas to the back yard (barbeque and fire fountain), and the other is inside the rocks in the fountain basin. Open the yellow valve attached to the house.
  3. Light Natural Gas
    The second valve inside the fountain basin allows the person lighting the fountain to throttle the gas while they light it. Start the barbeque lighter and place it 3 inches above the water surface, keeping your hand outside the perimeter of the fire bowl (lighter flame is 3 inches from bowl edge). Open the valve halfway (45 degree turn) and adjust lighter position to be above the bubbles. Gas will ignite and the flame will travel around the bowl until it is fully lit. Note All fuels can only burn within a spefic fuel/air ratio range. Natural Gas is mostly methane, which can combust only when the methane is between 5 and 15% of the surrounding air. Perhaps counter-intuitively, too much natural gas will put out the flame. For this reason, when lighting the fire fountain the lighter must be over 3 inches from the water surface. This lets the natural gas dilute to combustable levels.