It’s not the first thing you’d consider when building a fixed in-ground fire pit – but drainage is of course a big issue.
An in-ground fire pit will need drainage to stop it from filling with water and becoming a breeding ground for mosquitoes. If you line the bottom of your fire pit with lava pit rocks, fire pit glass, sand, or gravel, and install weep holes or a French drain, then it should drain well.
If your fire pit of any type is located on a flagstone patio, you may also need to install drainage under your seating area too or risk water pooling around your feet even if the fire pit itself remains dry. So there are a number of things for you to consider…
How Do You Keep Water From Pooling in a Fire Pit?
While many portable metal fire pits of large bowl design come with a hole in the bottom, this is to fuel the fire with oxygen from underneath rather than for drainage.
So to stop pooling water most portable models can be covered with a tarp or custom-fitted cover between use, then simply tipped out if needed.
It’s a different story with sunken fire pit drainage, and even if you cover them in the wetter or winter months, you can still get caught out with a rain shower in spring and summer – so it’s a good idea in this case to fit some kind of drainage option.
There are a couple of main ways of stopping your in-ground fire pit from flooding with rainwater, to avoid a messy gunk of wet ash at the bottom – so we’ll look at these below.
We’ll also consider when you should cover your fire pit and ow to measure it up for a cover that actually stops water ingress.
How To Drain a Fire Pit
As mentioned above – if you’re caught out with a rain shower with a portable fire put it’s easy to just tip out any excess water before your light the fire. However, it’s worth noting that the wet metal bowl should be dried off first before your set the fire.
For fixed stone constructed fire pits there are a couple of things you could consider that can be built into the base of the pit before you construct the main walls – and these are a French drain or weep holes. Let’s look at both.
When building your french drain under your fire pit, you have to take into account what you’re going to line the bottom with – whether that’s lava pit rocks, fire pit glass, sand or gravel.
We don’t recommend using conventional rocks or concrete as any water trapped inside can expand and explode when hot.
For the drainage channel itself you can use either a slightly angled 4 inch steel drain pipe to the open air some distance from the pit, or a gravel channel a few inches deep – again to reach daylight under the walls of the pit and then some distance away.
The great point about a French drain is that the channel your create can run under both your seating area and your fire pit, to stop water pooling in both.
Here are some example setups to avoid sand, dirt or ash blocking the drain – and also to stop the metal pipe (if used) getting too hot.
- Lava rock base – these obsidian rocks are formed from magma and are very good at conducting heat, plus they’re specially made for fire pits. If you’re using a metal pipe then you’ll need a drain grill cover over the top to ensure no debris goes down it, plus a few inches of sand or gravel so the metal pipe doesn’t get too hot. You’ll also need to use some durable fabric over the drain grill if your chosen heat diffusion layer is sand. If you’re using simple gravel for your drainage channel, then a layer of porous fabric is a good idea too under the sand/gravel – as this will stop any dirt clogging up your channel.
- Fire pit glass base – although not quite as good at conducting heat as lava rocks, artificially made fire pit glass does have the advantage that it comes in a variety of colors and looks great as a result. The same points apply though in terms of using sand/gravel for your heat diffusion layer – plus some tough fabric to stop debris going down either your metal drainage pipe or gravel drain. This option is rather more expensive than the suggestion above though.
- Gravel base – if you want to keep it simple and save money, then you could just line your fire pit with a few inches of gravel over either a fixed metal drain pipe or a further gravel drainage channel. If the pea gravel size is larger than the holes in your drain grill cover, you won’t need a fabric covering over the drain hole too (although it would still be advisable). Just make sure your gravel layer is a good few inches deep to shield any metal drainage pipes from the heat.
- Sand base – the cheapest option by far is to just cover a gravel French drain (or metal pipe drain) with some durable porous fabric, then cover this with a thick layer of sand several inches deep. However, this would possibly be the best option if your fire pit is a fixed but temporary structure. For fixed permanent stone fire pits, then the lava rock or fire pit glass options are best.
Another option for draining your fixed fire pit is to design in or drill slightly above-ground-level weep holes in the walls of your pit. These can then be used to clean out dirt and ash – as well as help with drainage.
The main downside to this over and above building a fixed French drain, is that the water and gunk can block the holes over time if you don’t regularly clean them out – or the dirty water can pool on your patio and around your feet in the seating area.
The great advantage of a French drain is that all the water is taken away from the location of your patio, and can be diverted some distance away. This helps create a more professional-looking fire pit and dining/seating area.
If you want the low down from Lowe’s on building a DIY in ground fire pit – including the sunken patio drainage – then this video covers it all:
Do You Need To Cover Your Fire Pit in The Winter?
The simple answer to this is yes – but it also depends on your specific year-round usage. Many people still use their fire pits to keep warm when sitting outside in the colder months, and if those months are wetter too then it certainly makes sense to cover your pit in-between lighting it up.
In the Fall you’ll also have to contend with falling leaves, and in the winter with a build up of snow (which then melts in the pit), so it’s a good idea to keep it covered for longer periods of disuse in certain seasons. The same applies when you go on holiday.
However, it can rain heavily in the spring and summer months too in some locations – so it’s good practice to simply cover your fire pit whenever it’s cooled down after use. It will just save you the hassle of cleaning out leaves, debris and any water that pools inside.
How Do You Measure a Fire Pit For a Cover?
Whether your have a portable metal bowl type fire pit or a fixed stone sided one, you can either cover it with a basic tarp or a custom-fitted fire pit cover.
The good news is that pre-made PVC coated polyester covers are not expensive, and come in a variety of sizes for many different styles of fire pits.
To measure your fire pit for a new cover, simply measure the diameter of the pit from its widest outside edge. To make sure your cover fits, it’s advisable to add at least 4 inches to this diameter measurement to be safe.
For example, if the diameter of your fire pit to the furthest outside edge is 42 inches – then you’ll need a cover measuring at least 46 inches .
Fire pit covers are durable, weatherproof and waterproof – and can be picked up quite cheaply at your local hardware store. It’s well worth the extra investment to prolong the life of your fire pit and save yourself a lot of hassle cleaning it out when you don’t need to.
Conclusion: Sunken Fire Pit Drainage
Although the question of whether your fire pit needs drainage seems like a simple one at first glance, there is actually a lot to take into account when considering your options.
It’s definitely a good idea to build in a permanent drainage system if you’re planning on installing a fixed stone fire pit. In addition, it’s also a great idea to keep both portable and fixed pits covered when they’ve cooled down when you’re not using them.
Whatever drainage option you decide to employ, there’s no doubt your investment in keeping the water out of your fire pit will save you time, money and hassle in the long run – and lead to many years of toasty times around the fire.
Homeowner and property investor Larry James founded Take a Yard in 2020 to bring you the very best outdoor living content, based on his years of experience managing outside spaces. Read more >