Outdoor fireplaces have become immensely popular over the years, and as such, there are now numerous types and designs. You can get yourself fire pits, fire bowls, gas fireplaces, wood-burning fireplaces, and even electric fireplaces, but do outdoor fireplaces need a smoke shelf?
Outdoor fireplaces should be fitted with a smoke shelf if they are gas or wood-burning. Smoke shelves prevent smoke from coming out the front of the hearth, which is important regardless of whether the fireplace is inside or outside.
Smoke shelves are generally good practice, especially for outdoor fireplaces, as the wind flow can be unpredictable outdoors. This article will look at what smoke shelves are, how they work, and why it’s recommended to have them!
Do Outdoor Fireplaces Need A Smoke Shelf?
A smoke shelf is not required for outdoor fireplaces but is recommended. Smoke shelves ensure that the smoke produced by your fireplace doesn’t blow out via the front. Outdoors, the wind flow is unpredictable, so there’s always the chance of smoke blowing in your seating area. Smoke shelves can prevent that.
Smoke shelves are shelves in the flue or chimney that prevent smoke from blowing out of the hearth. They kind of ‘catch’ the wind, which ensures that no smoke is blown into the room the fireplace is located in. Just imagine if all that smoke went straight into your home instead of up the chimney.
So if smoke shelves were designed to keep the smoke out of a room, why would you need one outside?
Well, outside fireplaces commonly have a seating area around them, and despite you all sitting outside, it’s still not fun to constantly have smoke blown into your face every time the wind changes.
And that’s where smoke shelves help.
They will catch the wind halfway through, making sure it’s not a clear path to the hearth of the fireplace. This prevents the smoke from blowing out the wrong end and will make for an overall nicer and safer experience.
Why Does an Outdoor Fireplace Need a Smoke Shelf?
Fireplaces produce smoke, and unpredictable wind flow can blow all the smoke out via the hearth. Indoor fireplaces are in a controlled environment with little wind. The outdoors is less predictable and controllable, but a smoke shelf can help regulate the airflow and prevent smoke from blowing into the outdoor seating area.
It really comes down to the fact that outdoor fireplaces are in much less predictable locations. Inside, there’s hardly any wind, and since hot air rises, the smoke will simply make its way through the chimney and outside the home.
Outside, however, even a small breeze can cause the smoke to propel out from the hearth.
Without a smoke shelf, it would also be a straight shot from the top of the chimney to the firebox, and these sudden blows of wind are not only annoying but can also be dangerous.
Not only will smoke be blown into the seating area (smoke contains toxins), but the sudden increase in oxygen can also increase the flame.
There are a few alternatives for smoke shelves, which we’ll touch on shortly, but smoke shelves really are the easiest and most reliable option to prevent all this.
Do You Need To Clean A Smoke Shelf?
Smoke shelves should be cleaned as there can be a build-up of debris, water, ash, and creosote. The smoke shelf is located right above the firebox, so it’s an easy spot for ash and creosote to build up, and rainwater and other debris can easily make it’s way down there. Smoke shelves are typically included in a regular chimney sweep.
Smoke shelves are notorious for retaining all sorts of by-products. Since it’s located right above the firebox, there will be a lot of smoke and ash passing through. And due to the shelf-like nature of the smoke shelf, a lot of ash will end up staying there.
Back in the day, smoke shelves were built with a technique called corbelling. What this created was a structure with many tiers and layers within the actual shelf. And every one of these layers provides an excellent place for creosote and ash to build up.
On top of that, a lot of different layers and tiers create a lot of masonry joints, and if there’s a lot of ash or creosote build-up, these masonry joints will eventually deteriorate.
It’s also a straight shot from the top of the chimney to the smoke shelf, so anytime it rains, the rainwater will make its way down to the smoke shelf.
In short, if the smoke shelf isn’t cleaned every once in a while, it can get really messy there.
A good chimney sweeping service will take care of it right after sweeping the chimney. This is especially important because a lot of ash and debris will fall down the chimney shaft when it’s swept. If your smoke shelf isn’t cleaned after a chimney sweep, there will be even more build-up.
And in the case of creosote, it’s actually quite dangerous since creosote is highly flammable.
What Are Some Alternatives For A Smoke Shelf?
Smoke shelves don’t have to be large, but sometimes, there’s just no space for one. Or maybe you just bought a new house that came with an outdoor fireplace that doesn’t have a smoke shelf.
Luckily, there are some alternatives for smoke shelves.
1. A Wind Cap
Since smoke shelves primarily help prevent the wind from blowing smoke out of the wrong end, a wind cap might be a good alternative.
The main issue is that wind blows into the chimney, and the sudden change in the direction of airflow causes the smoke to come out the wrong end.
By installing a chimney cap, you limit the surface area where the wind can go inside the chimney. By giving the wind less space to go inside the chimney, there will be fewer instances where the wind carries the smoke in the opposite way.
2. A Narrow Flue
Another way of decreasing the chances of wind blowing inside the chimney is by having a smaller flue.
The only problem here is that a flue needs to adhere to certain sizes and specifications.
12.4.4 (1) The cross-sectional area of the flue shall not be less than the cross-sectional area of the appliance flue collar, unless specified by the appliance manufacturer.Source: NFPA-211
A smaller flue decreases the surface area in which wind can blow in the chimney, but it also reduces the amount of space from which the smoke can escape.
This could lead to smoke spilling into the air intake and from smoke building up near the top of the flue.
Ultimately, a wind cap is by far the better option, but a more narrow flue can be an option. Just make sure to discuss that with a local fireplace specialist, as these rules and specifications can vary from country to country and state to state.