Whether you’re burning wood in a fireplace, fire pit, or in the stove box of your wood heated hot tub, the type of firewood makes a big difference to the overall quality of your fire. The best firewood will:
- Generate a good amount of long-lasting heat
- Burn efficiently and not quickly
- Produce minimal smoke
- Create a safe fire
There’s a decent amount of science around the burning of wood but in the interest of time - you have a wood fired hot tub to heat up and sink into - we’ll keep it simple and practical.
The Firewood Factors
The first key point: not all wood makes good firewood. In fact, some types make terrible firewood. For an extra-toasty fire—or maximum heat output—and minimal environmental impact, the two most important firewood factors are:
- Water content
Dense, dry firewood burns the best. It’s a ‘clean burn’ producing high heat and low smoke. In general, hardwoods tend to be more dense and contain less moisture—we’ll go into this in a little more detail below.
Wood with higher water content will struggle to burn while producing a lot of smoke and releasing additional pollutants into the air.
Image: Illustration ‘Quercus robur’ (oak) 1885 via wikimedia commons
Types of Wood
The three broad categories of wood are hardwood, softwood, and engineered wood. This last one has no business being in a fire.
Hardwood is from deciduous trees with leaves and seeds like fruit trees, oak, maple, and walnut. Softwood is from evergreen or conifer trees which produce needles & cones like cedar, pine, redwood, and spruce.
Despite the name, “softwood” isn’t truly soft to the touch. It’s less durable than hardwood, but some softwood lumber like western red cedar is used for construction and hardwearing outdoor applications. Softwood is faster growing, easier to source, and considered a very renewable resource.
Hardwood Firewood vs. Softwood Firewood
If you know your woods well, hardwood will always be your first choice for firewood. Dense hardwoods burn longer and produce more heat, making an excellent choice for heating purposes. Hardwoods are also less resinous, meaning they’re less likely to create a build-up of black residue (known as creosote) in your stove box or chimney.
Hardwood firewood provides a steady, lasting burn with minimal smoke. Additionally, they tend to produce a bed of hot coals which can be used to maintain a consistent temperature.
Softwood is incredibly useful as kindling. Conifers have a sticky substance (sap, pitch or resin) beneath their bark that seems to make it easier to burn. Softwood catches fire and burns quickly, while hardwood is difficult to ignite. One downside is that resin doesn't directly burn off and tends to build up as creosote.
Pine and cedar are often chosen as firewood because they’re readily available in the forest, create an attractive flame, and have an enjoyable scent. Regrettably as softwoods, they make a lot of smoke and a short-lasting burn.
Your Best Firewood Plan
- Use softwood as kindling
- Utilize hardwood as fuel - once the fire is established and there is some heat in the base of the fire, hardwood will maintain a slow-burning fire with a good heat output
Image: Roya Ann Miller via unsplash
What Causes Smoky Fires?
We touch upon the science of smoke in our article on Eco-Friendly Hot Tubs along with recreational fire smoke and its effects on the environment. We believe a properly built and managed fire has minimal or no smoke.
So what causes some fires to be smokier than others? If you burn the wrong type of firewood, or if not enough air gets to the fire—known as incomplete combustion–you’ll produce smoke.
The small, unburned particles of wood that smoke carries upward and deposits on the walls of your wood burning appliance is called creosote. When there’s too much buildup of this residue over time it becomes a fire hazard, and can catch fire.
Firewood to Avoid
Remember “not all wood makes good firewood”? It can be very tempting to burn waste wood or whatever refuse you’d like to clean up on your property. Steer clear of:
- Treated wood (includes manufactured, engineered wood and plywood) - releases harmful chemicals when burned
- Green or new wood which hasn’t been properly ‘seasoned’ - can produce a lot of smoke and burns inefficiently
- Wet or damp wood
- Driftwood (marinated in sea salt) or sandy wood
Be aware for safety reasons that some species of woods are known to throw more sparks, such as hemlock. This is due to the resin or sap. Sparks and crackling are also signs of wood that’s not dry enough to burn.
Image: Green wood visual comparison by Surryroger via wikimedia commons
How to Tell if Wood is Dry Enough
The term ‘seasoned’ wood means it has gone through the process of drying. The firewood is left outside for at least six months in a covered area with good air circulation. Firewood can also be kiln dried.
There are a few ways to decipher if your firewood is dry enough to burn efficiently:
- Visible cracks in the end grain
- Wood colour changes from white to grey or yellow/orange (depending on the species)
- It sounds hollow if two pieces are banged together
- When split it’s dry to the touch inside
- Bark easily pulls away in one piece
Best Firewood By Region
To recap some previous points, in general the best firewood is hardwood because it’s denser, has low resin content, and lower moisture. This type of firewood burns cleanly, hot and slow, making it popular for heating. Depending on where you live, maple is a good firewood choice along with oak and ash. Below is a partial list of the best regional hardwoods to use as firewood.
Western hardwood species:
- Oak - Live oak, Oregon white oak, California black oak, Garry oak
- Maple - Bigleaf maple, red maple, soft maple
- Pacific madrone
- Red alder
- Oregon ash
Source: Dead oak tree by Phillip Harding via wikimedia commons
Eastern hardwood species:
- Black birch
- Locust - Black locust, honey locust
- Oak - Northern red oak, white oak
- Sugar maple
- White ash
If you can’t get your hands on hardwood firewood in your area, consider a ‘hard softwood’ that provides high heat (but burns quickly). Douglas fir, juniper and yew are considered hard softwoods.
Remember that regardless of the type of firewood, proper seasoning and storage are essential to ensure it burns cleanly and produces minimal smoke.
Additional Firewood Tips
Here are a few of GOODLAND’s top firewood and fire-building tips:
- Buy wood from a reliable supplier and inspect before buying it. It should be well seasoned, split, locally-sourced and relatively clean, i.e. no pests, sand, mold, etc. Don't be shy about asking how long it's been seasoned for and where it's from.
- Ideally buy cords of wood in the early spring and stack it on your property to control the seasoning process. It should be ready to burn in the fall.
- Not sure how to stack wood? Read this popular post on the best way to stack firewood from our sister company, Union Wood Co.
- Firewood will need to be split into smaller pieces to fit into your hot tub's wood stove and to ignite more easily, and burn efficiently. We recommend no more than 16” long and 4” wide. Keep in mind that hardwood isn’t easy to split—make sure you have a good quality axe.
- Setting a successful fire takes a little practice, watch this short video for pointers on starting a fire.
Gradually build your fire up by slowly adding slightly larger pieces and adjusting the ventilation with the lid to the stove box. Don’t overstuff the fire so you can ignore it—the process of maintaining the fire is part of the wood fired bathing experience. If curious, learn more about how wood stove hot tubs work.
Cleaning the Wood Stove Firebox
The last step to help your firewood burn more efficiently is to remove the ashes from your stovebox after every few fires. Setting a fire in a ‘clean’ firebox also prevents soot build-up.
Use an ash scoop to easily remove the ashes, or a small shovel and metal bucket. Be sure to wait for the stovebox to cool before handling ashes, and to safely store/dispose of them—ashes can reignite very easily especially in dry, hot climates when left in heaps.
Hot tip: Put the ashes to work in your garden and around the home. Check out The Farmer’s Almanac for articles on using wood ash to improve your soil, compost, and to repel slugs. We also found a helpful list of 13 Clever Things You Can Do with Fireplace Ashes if you use your wood fired hot tub on the daily.