Cheap DIY Outdoor Fireplace: Complete Guide for Homeowners

Contractor-built outdoor fireplaces routinely run $5,000 to $15,000, which is a painful number for something you use two dozen evenings a year. A cheap DIY outdoor fireplace built from standard cinder block, firebrick, and mortar can come in at $150 to $400 in materials and a single weekend of labor. It will not have the custom masonry of a mason-built hearth, but it will throw real heat, hold a 16-inch log, and last a decade if you follow a few fire-safety rules. Here is the full build, the materials list, and the mistakes that make first-timers tear it down and start over.

Design Basics and Footprint

The simplest effective design is a three-sided U-shape about 48 inches wide, 24 inches deep, and 60 inches tall. The opening faces your seating area. Inside, a firebrick-lined firebox protects the cinder block shell from direct flame contact. Total footprint fits on a 5 by 4 foot concrete pad, which keeps your pad cost under $100 in premixed concrete or pavers.

Complete Materials List Under $300

• Concrete cinder blocks, 8x8x16: 40 blocks at $2.50 each — $100
• Firebrick, 9×4.5×2.5: 30 bricks at $2.75 each — $82
• Refractory mortar (Rutland or similar): 1 bag — $25
• Type S masonry mortar: 2 bags at $10 — $20
• Concrete pad bag mix: 6 bags at $5 — $30
• Rebar, #4 (1/2 inch) 20-foot lengths: 2 at $8 — $16
• Metal fireplace lintel or 1/4 inch steel plate: $25
• Miscellaneous: sand, gravel, level, trowel: $30

Total: roughly $328 if buying every item new. Source used cinder blocks from a Craigslist demo or Habitat ReStore and the build drops under $200.

Site Prep and Code Check

Call your local building department before digging — many jurisdictions require a permit for any permanent outdoor fire feature and set minimum clearances of 10 to 25 feet from structures, decks, and property lines. HOA rules can be stricter. Place the fireplace on level ground at least 15 feet from the house, away from overhanging trees, and upwind of typical seating so smoke blows away from guests.

Step 1: Pour the Concrete Pad

Dig a 5 by 4 foot hole, 6 inches deep. Fill the bottom 2 inches with gravel for drainage. Set 2×4 forms around the perimeter, level them, and pour 4 inches of concrete mix. Embed two pieces of rebar in an X pattern in the middle of the pour. Screed flat, float smooth, and let it cure 48 hours before adding weight.

Step 2: Dry-Stack the First Course

Lay the first course of cinder blocks dry, without mortar, to check alignment. A 48×24 inch firebox requires three blocks across the back wall and two blocks on each side wall. Adjust until everything squares up and the front opening measures 32 inches wide. Mark the block positions with chalk before mortaring.

Step 3: Build Up the Outer Shell

Mix Type S mortar to a peanut-butter consistency. Lay a 1/2 inch bed under each block, butter the vertical joints, and stack courses, staggering the joints like a running bond. Check level and plumb every course. Build up 7 courses — roughly 56 inches — to reach chest height. Use full 8-inch blocks for most of the shell and half blocks where you need to stagger joints at the corners.

Step 4: Line the Firebox With Firebrick

Starting at the pad inside the cinder block shell, dry-stack firebrick to form the firebox floor and three walls. Use refractory mortar only — standard mortar cracks above 500°F and your firebox will hit 1,200°F easily. Leave a 1/2 inch air gap between the firebrick lining and the cinder block shell, filled loosely with fireplace-rated insulation or left empty. This gap keeps heat away from the cinder block, which otherwise spalls and cracks at high temperatures.

Step 5: Install the Lintel and Cap

Across the front opening at roughly the 4th or 5th course, set a steel lintel or 1/4 inch steel plate as a bearing beam for blocks above the opening. Continue laying the upper courses over the lintel to form the smoke shelf and chimney stack. Cap the top with a single course of cinder block turned on its side, or a poured concrete cap for a cleaner finish.

Step 6: Seal and Cure

Let everything cure 5 to 7 days before the first burn. Skip this and trapped moisture in fresh mortar will steam-expand during the first fire and crack everything you built. Burn three small, gradually hotter fires (starter logs only) before loading it with a full split-wood fire. This tempers the refractory mortar and the firebrick properly.

Safety Rules That Prevent Disaster

• Never use regular concrete block as a firebox liner — it explodes under heat
• Keep a fire extinguisher and a connected hose within 10 feet
• Burn only seasoned hardwood, never pine, pressure-treated lumber, or pallets
• Allow a 3-foot clearance zone on all sides free of furniture and fuel
• Put fires out completely before leaving — douse with water or smother with sand

Cost-Saving Alternatives

If even $300 feels steep, a single ring of cinder blocks set on a gravel pad makes a functional $80 fire pit — not a fireplace, but warm company on a cool night. Paver stone kits from Home Depot (Pavestone Rumblestone, for example) build a similar fire ring for $150 with no masonry skills needed. These options skip the chimney draw but work fine in open yards with steady breezes.

Finishing Touches

A coat of heat-rated stucco or a stone veneer disguises the raw cinder block. Cultured stone veneer panels run $7 to $15 per square foot and transform a boxy block fireplace into something that reads custom. Add a $40 cast iron grate, a $25 spark screen, and a pair of $15 fireplace tools to complete the build.

A cheap DIY outdoor fireplace is absolutely achievable on a real-world budget. Respect the fire-rated materials, honor the code clearances, and cure everything properly — and you will have a heat source worth a dozen evenings each year for a decade or more.