Start by designing a pixelated fire pattern. This will be your pixel map. I went for a 1980s videogame-style flame.

Measure your fireplace. Calculate how big each pixel will be by dividing the height/width of your fireplace by the number of pixels. Mark a pixel grid on your plywood/canvas.

Use your pixel map to label each individual pixel - it will save you time and confusion of having to constantly refer to your map later on when painting.

Paint the color layers from the outside in. Use painter's tape to mask the edges.

After the outer black pixels are dry, we are ready to start painting the red pixels.

Paint using a regular brush or a sponge brush, as shown here. For lighter colors apply 2-3 coats. Make sure the paint is completely dry before peeling the tape, or it WILL bleed through.

For lighter colors (anything that's not black) you'll want to erase the pencil markings before painting, to prevent them from showing through like the "R" in this picture.

Red is done. While the paint dries, rinse your brushes and let them dry out too, so they are ready for the next color (or use multiple brushes).

Now the next layer - yellow.

Finally, the white highlights.

Make absolutely sure the paint is completely dry before peeling the tape.

Perfect square pixels.

Peel the final pieces of tape, admire your work. You are very talented!

Install the pixelated flame in your fireplace. No need to light, add firewood, gas, or put out the fire before going to bed. Voilà! Enjoy your new energy-saving fireplace.