Lava rock vs fire glass comes down to look, budget and weight. Lava rock is cheap, light and rustic, and it hides gas fittings. Fire glass costs more, is heavier for the same volume, and looks modern. Both work in a gas fire pit or fire table when rated for fire use, and many people use both: lava rock as a base with glass on top. This guide covers gas fire pits, fire tables and vented gas fireplaces whose maker approves loose media. Never put either in a wood fire. For electric fireplaces, see fire glass vs a log set for an electric fireplace.
Lava rock vs fire glass at a glance
| Factor | Lava rock | Fire glass |
|---|---|---|
| Look | Natural, matte, brown to black, rustic | Clean and modern; colors and reflective finishes catch the flame |
| Price on our site | About $2 per lb (HPC Fire small lava rock) | About $5.50 per lb (Empava 10 lb bag) |
| Weight for the same area | Our HPC Fire lava rock listing says 10 lb fills as much area as 20 lb of fire glass | Roughly twice the weight of lava rock for the same space |
| Moisture | Porous, holds water; let it dry before lighting | Does not soak up water, but still let the pan drain and dry |
| Cleaning | Porous, harder to rinse clean | Dust can be rinsed off with water |
| Best use | Base layer, filler, rustic look, hiding piping | Top layer or full fill where you want a finished look |
Look and heat
Lava rock looks like a campfire bed and its natural color varies from brown to black. Fire glass reads contemporary, and its color shows even when the burner is off. Media does not create heat; the burner and gas input do. For example, HPC Fire’s specification sheet for its Torpedo H-burner lists a recommended range of 150,000 to 200,000 BTU for the 36 x 8 inch size. Pick media for looks, weight and budget.
Cost: compare per pound and per volume
At the time of writing, HPC Fire small black lava rock (1/4 to 1/2 inch), 20 lb is listed at $40 and the 10 lb bag at $20. The Empava 1/2 inch Shimmer Gold tempered fire glass, 10 lb is currently listed at $54.79. Empava sells the same bag on its own site at the same price with free shipping, so if glass is all you need, Empava’s site may be cheaper; ordering here makes more sense alongside a burner or kit.
Per pound, glass costs a little under three times as much. Per volume the gap is bigger, because our HPC Fire lava rock listing states a 10 lb bag fills as much area as 20 lb of fire glass. That is why builders often fill a deep pan with lava rock and save glass for the top.
How much fire glass do I need?
- Measure the area in square feet: for a rectangle, length times width in inches, divided by 144. For a round pan, multiply the radius in inches by itself, then by 3.14, then divide by 144.
- Decide the depth in inches from your burner manual (see the next section).
- Multiply square feet by inches of depth by 8. MSI’s fire glass specification sheet says a 10 lb bag covers about 1 square foot at 1.25 inches deep, which works out to about 8 lb per square foot per inch.
Example: a 36 x 14 inch pan is 504 square inches, or 3.5 square feet. Filled 2 inches deep with glass, that is 3.5 x 2 x 8 = 56 lb. If you put a 1 inch lava rock base under 1 inch of glass, you need about 28 lb of glass plus roughly 14 lb of lava rock, using that half-the-weight rule. Glass size and shape change the figure, so check the coverage note for your product and round up.
Depth over the burner: follow your manual
Makers disagree. MSI recommends at least 2 inches of its glass over the burner so gas filters evenly. Celestial Fire Glass suggests about 1/2 inch of glass on top of the burner. The Dekko fire feature manual says to avoid covering the burner holes as much as possible. Your burner or fire table manual is the authority: if it gives a depth, use it; if it says not to cover the ports, do not.
Can you mix lava rock and fire glass?
Yes. Our HPC Fire listing describes the small lava rock as a base material under 1/2 inch fire glass or fire beads, and as a way to hide gas piping. Some kits include lava rock already: the HPC Fire H-burner MLFPK Torpedo hardscape block kit, 36 x 14 inch propane, is a match lit insert rated up to 65,000 BTU that ships with lava rock to lay over the burner. It is listed at about $2,397 at the time of writing.
If you are building your own pit, a bare burner such as the HPC Fire Torpedo H-burner, 36 x 8 inch propane or the 36 x 8 inch natural gas version (both about $238 at the time of writing) suits layered media. Order the version for your fuel type, and have a licensed gas fitter make the connection to local code.
Is lava rock safe in a fire pit? Wet media and popping
Lava rock is made for fire features, but it is porous. The Dekko fire feature manual warns that moisture can make stone pop or crack when heated, says not to use the fire pit when the stones are wet, and says to inspect and discard stones with hairline cracks before placing them. Our fire pit buying guide covers placement and safety for the whole pit.
- Use a cover between uses.
- Make sure the pan or enclosure drains. HPC Fire’s H-burner spec sheet calls for a hole of at least 6 inches across in the bottom of a bowl.
- After rain, let the media dry before lighting.
- Vent the enclosure as the burner maker specifies. HPC Fire lists at least 2 vents of 18 square inches each, on opposite sides, for pits up to 200,000 BTU.
Reflective vs regular fire glass
Regular fire glass has a frosted or translucent look. Reflective glass has a mirrored face that throws back more of the flame at night. Neither changes heat output, so choose by look.
One caution: Amantii’s reflective and bead fire glass bags on our site are described by Amantii as media for Amantii electric fireplaces, so we do not recommend them for gas fire pits. For gas, choose glass labeled for fire pits, like the Empava bag above.
Fire glass for a gas fireplace
Some vented gas fireplaces accept glass or lava rock in place of logs; many do not. Use only media the manufacturer lists for that model, in the amount the manual allows, and have a qualified technician confirm any change. For outdoor units, our outdoor gas fireplace guide covers fuel, clearances and installation.
Frequently asked questions
Which is better, lava rock or fire glass?
Neither adds heat. Lava rock wins on cost and weight; fire glass wins on looks. A lava rock base under glass gives you both.
How much fire glass do I need for my fire pit?
Square feet times inches of depth times about 8 lb, using MSI’s coverage figure, at the depth your burner manual specifies.
Why does lava rock pop in a fire pit?
Water trapped in porous stone turns to steam when heated. Keep the pit covered, make sure it drains, and do not light it while the media is wet, as the Dekko fire feature manual advises.
Can I use fire glass in a wood burning fire pit?
No. Fire glass and lava rock are for gas burners only.
Browse more HPC Fire burners and media, or call us at 866-777-2590, Mon to Fri 9AM to 6PM PST, for help sizing a burner and media. We offer free freight shipping on orders of $999 or more, with a $200 flat rate below that. See our return and refund policy before you order.
