How to Make a Modern Outdoor Fireplace

It’s surprisingly easy to build—and portable, too.

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Introduction

This project was inspired by an outdoor gas fireplace I saw online. The look was exactly what I wanted, but the construction wasn’t—I didn’t want a 500-lb. concrete cube that couldn’t be moved. And I didn’t want an underground gas line to fuel the fire. So instead I engineered this version. It looks just like the one online, but it can be easily moved by two people and it doesn’t need a remote gas supply. Best of all, it’s an easy weekend project, suitable for a beginning builder.

Tools Required

  1. Basic hand tools
  2. Drill/driver
  3. metal snips
  4. Rasp
  5. Saw

There’s a secret inside this outdoor fireplace

This outdoor fireplace looks like a solid concrete cube, but this hollow box holds a standard propane tank and regulator—the same components that fuel a typical gas grill. Just remove the burner and lift out the tank when it needs to be refilled. The door provides access to the burner controls.

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It’s really easy, but …

This outdoor fireplace project involves mostly cutting parts and driving screws—simple stuff. But it does include some materials and methods that might be unfamiliar to you:

  • STEEL STUDS are the best choice for the inner structure of the box. Unlike wood, they’re unaffected by heat and humidity. If you haven’t worked with steel studs before, don’t worry—you’ll probably find them easier than conventional lumber. For tips on building with steel, search for “steel studs” at familyhandyman.com. Note: Steel studs in contact with soil will eventually rust away, so the box base is pressure-treated wood.
  • BACKER BOARD, normally used under ceramic tile, forms the outer shell of the box. I used 1/4-in.-thick GreenE-Board, which is made from lightweight magnesium oxide. Any exterior-rated backer is fine, except versions that have a foam core, which may not stand up to heat.  For information on types of backer board and how to work with it, go to familyhandyman.com and search for “tile backer.”

The fuel and flame system

Propane burners are available online in various sizes and shapes. I used a 19 x 19-in. stainless steel version with a built-in igniter. The AZ GSF burner connects to a standard  20-lb. propane tank, which provides about 20 hours of use.Some burners have a control panel that can be mounted on the exterior of the fireplace. Mine didn’t, so I installed an 8 x 8-in. stainless steel access door (Acudor ED-2002). I glued the door in place with construction adhesive.

Decorative “fire pebbles”fill the burner tray. To protect the burner from rainwater and other elements when not in use, I applied foundation coating to a leftover scrap of backer board.

Foundation coating

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Foundation coating covers the backer board on this outdoor fireplace. It’s kind of like super-thick paint mixed with fine sand, so it gives the look of concrete without the weight and backbreaking labor. I used FlexCoat, which is available in various colors. Before brushing on the coating, wipe dust off the box and apply backer board tape to the corners. The tape may not stay in place for long, so apply the coating right away.

Cutting List

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Outdoor Fireplace Plans

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WARNING: Ventilation is mandatory: A gas leak would fill the box with propane. That’s a potential explosion. To ventilate the box, I used a hole saw to bore four 1-in. holes on two sides of the box. That way they’d be hidden by the deck but still allow leaked propane to escape.

Project step-by-step (7)

Step 1

Build Four Walls

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Slip each stud into the tracks, clamping them into place with locking pliers. Drive screws on one side of the wall only. Place the end studs with the open side facing inward.

Step 2

Assemble the Box

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Build a base from pressure-treated 2x4s and screw the walls to it. Make sure the screw heads on each wall face into the box. A layer of window flashing tape protects the steel from the corrosive chemicals in treated wood.

Step 3

Join the Walls

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Align each corner of the box carefully so the adjoining end studs form a perfectly flat surface. Then screw the walls together at the end studs.

Step 4

Add Top Supports

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To reinforce the top of the box, add steel studs inside the upper tracks. Set the supports on brackets screwed to the tracks or adjoining supports. Make the brackets from leftover studs. No need to screw the supports to the brackets; adhesive will secure them when you add the backer board top.

Step 5

Skin the Box

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Apply plenty of construction adhesive to the wall framing, then screw on the backer board. Cut the access door hole after the backer board is in place.

Step 6

Round the Corners

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Round all the corners of the box with a rasp or a coarse file. Rounded corners look better than sharp edges and are less likely to chip.

Step 7

Coat the Box

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Apply mesh tape to the corners and brush foundation coating over the tape. Also dab coating over the screw heads. Then give the entire box two coats of foundation coating. When the coating dries, you’re ready for a fire! Check out these other fire pit ideas you can DIY:
Brick fire pit

Stone fire ring

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