Your First Fire Place:
If you are like me, your first experience with a fire pit was most likely on a camping trip as a child. And if you had camping experiences like I did, you’ll probably always remember fire pits fondly. The warm glow, the family stories, the shared experiences are all a part of the fire pit experience. What makes fire pits one of the best amenities for a landscape is the fact that you can share the experience with a large number of people. While a regular fire place is similar in many ways, it is very hard to get more than a two or three people comfortably in front of a fire place. And when more than three people line their backs to a fire place, the other guests can’t see the fire anymore and anyone not in the first row gets little or no heat. On the other hand, a fire pit, especially a larger one can easily accommodate five or six people or even more. I have seen some large fire pits at ski resorts that were ten feet in diameter and could easily accommodate fifteen cold skiers.
In addition a fire pit can allow for built-in fire side seating. By placing a wall around a fire pit and making the circle large enough people can sit around its edge. Just be sure the fire ring is large enough to place the fire safely in the middle away from the edge and with sufficient room so seated guests don’t get too hot. A fire circle typically needs to be at least six feet in diameter or greater for safe fireside seating.
Sizing your fire pit:
In my experiences I have designed many fire pits including several for my own homes. The most typical size that I have used for a small residential fire pit is an outside diameter of about four feet. This allows for about five or six people to stand near enough to the fire to keep warm on even the coldest nights. Generally speaking, you can use the formula for the perimeter of a circle (2 x pie x radius) to determine how many people can enjoy the fire at one time. Simply determine the perimeter based on your proposed fire pit diameter or radius then divide that by three feet. The resulting number is approximately how many people will stand comfortably near the fire pit. For seating divide the number by 2.5 feet or 30”.
For 3-4 people a 3’ diameter fire pit is good
For 4-5 people a 4’ diameter fire pit is good.
For 6-7 people a 6’ diameter fire pit is good.
For 8-10 people a 8’ diameter fire pit is good
For larger pits please use the formula: #of people = (2×3.14xradius of fire pit in feet) divided by 3feet
Designing the right wall height for your fire pit:
Now that you have the size of your fire pit in mind let’s talk about the height. The height of the fire in your fire pit is very important. If the fire is too high you may lose most of the ambient heat to the atmosphere before it reaches your guests. Also if your fire well is too low and the walls around the fire pit are too high the heat will be funneled and reflected upward and not reach the guests standing around the fire pit. The key is to balance your need to contain the fire with your desire to provide heat to the seating areas around the fire pit. If you want to provide a lot of heat and are not worried too much about fire spilling out, such as cases where the fire is a natural gas fire with gas burning logs, you may not need a low wall around the fire at all.
Fire height in the fire pit:
I have seen some very large fire pits placed in shallow depressions only a few inches deep, with seating placed tightly around the edges to ensure people don’t walk into the fire. There was no walking space between the fire and the log benches; this ensured that there was little to no chance people would walk around the edge. This was a good design for a large ski resort where they wanted twenty or more guests to sit around the fire pit. However, in a back yard fire pit you may have small children, no access to natural gas or other concerns, so a low wall is often best design style fir a residential fire pit. I typically recommend a low seat all from 12” tall to 24” tall. Also I recommend that the base or tray for the fire be placed just 6-12” below the top level of the wall around the fire. A common mistake is to build a 24” high wall and leave the fire down at the bottom of the pit. This reflects most of the heat straight up and makes the fire pit very inefficient at heating your guests. By raising the burning wood to a level nearer the top, more heat is reflected outward. However, you must be careful you are not burning wood that pops and blows burning pieces out of the fire often. Note: A wall 18” height is perfect for seating. If you want to provide a seat wall and encourage seating be sure the pit is larger so that you can provide 2-3 feet from the edge of the flame to the seating. The width of a seat wall should be at least 8” and 12-18” is best.
Air flow for a fire pit:
When considering the height you must also take into account air flow for the fire. A fire behind a wall needs air to burn effectively. I recommend that several small holes 2-3” in diameter be placed around the base of a fire pit. On average you should provide approximately one 2” hole every 2-3 feet to provide adequate air for the flames. Note: If you are building a fire pit out of brick then you can simply leave out a ½ brick or turn one on its side if it is the kind with the holes in it. If you are using stone and masonry you may need to knock out a hole in the block and or brick and use a steel pipe. Note: don’t use any pvc or plastic pipe for air penetrations because it will burn.
Lining your fire pit with fire brick:
In addition to venting for you fire pit you should also be sure to use fire rated materials for the lining of your fire pit. Note: if you use typical concrete masonry units (CMUS or Cinder blocks) they will often crack and can even explode if water gets trapped inside and heats to rapidly. The best thing to use is “fire brick”. This is a clay based masonry unit that is specially high fired at very high temperatures to make it very dense and safe for use with fire. Also use fire rated mortar to join the fire brick to the rest of the masonry in your fire pit. You can veneer the outside of the fire pit with stone or brick for a really nice look. Cap your fire pit with 2” thick or thicker real stone and be sure not to cantilever the edge over the fire as this can lead to a really hot edge and cracking stone.
Draining fire pits:
Draining fire pits can also be problematic. Where possible try to install a steel drain pipe 3-4” diameter into the floor of your fire pit. I have used common shower drain caps to cover my drains. Note: You can usually purchase steel pipe and drain caps at local hardware or home stores. If you cannot do this then be sure the bottom of the firepit has a gravel sump in the bottom at least 12” diameter and filled with stone. This will allow rain water to slowly percolate into the soil beneath. If you cannot do either of these things then you will need to shovel out the fire pit often and suck out water trapped inside so the pit does not become too wet to use.
Placement of fire pits:
Placement of a firepit is also very important. A fire pit should never be less than 10 feet from any combustible material, wall or building. I recommend all fire pits be on patios of stone, pavers, gravel, etc. And you should maintain a clear area around the fire pit free of organic materials. No dry plants, leaves or mulch should be near a fire pit. Wood chairs are generally safe but metal is best. Note: Never leave a fire in a fire pit unattended. Never stack wood near enough to a fire pit that a burning ember could land on it.
Summary of design and construction tips for building a fire pit:
Summary: A fire pit needs to be designed for the appropriate location and number of users. The fire bed should be the appropriate height to ensure efficient burning. Clear zones are needed around all fire pits. All fire pits should have air holes and drains. Seat walls can be nice additions to a fire pit. Fire pits are traditionally built out of stone, brick and masonry.
Other options for fire pits:
Finally, there are lots of options for fire pits including store bought chimineas, fire bowls, portable fire places, outdoor fireplaces and more. Be sure to research the rest of this site and other posts for more ideas on these features. A chiminea is a pre-manufactured fire element. Many of these are made of clay and fired. Also there are lots of bowl like elements that sit on legs sold at home stores.