The truth behind moisture content
The biggest mistake you can make when buying firewood is not understanding how much the dryness of the wood matters.
One of the biggest myths we have heard from time to time is "Kiln Dried burns away too quickly"
It's always difficult to hear because they are literally telling us that our wood is better than what they are used to, but would prefer something that's less efficient, less capable of heating the house, and costs them more in the long run!
Let's dive into the science of burning firewood and well and truly put this one to bed!
To heat your home with firewood, you start with kindling. Once it's going, you add larger pieces.
The heat warms the wood until it reaches pyrolysis — the point where wood turns to gas. That gas ignites, releasing more heat, which drives more pyrolysis — and so the chain reaction continues until the wood is spent.
Now let's dig a little deeper!
Each piece of wood has some water in it. How much exactly? Well that depends, but it seriously matters!
As the amount of water in the wood goes up, the amount of energy in the wood that goes into your home goes down.
This comes down to two key concepts, the energy consumed to evaporate the water, and the gases lost up the chimney due to inefficient combustion (the chemical reaction is more effective at higher temperatures, but evaporating water cools everything down)
Think of it this way - For each piece of firewood you have, you need to and cut off a bit at the end. Think of this smaller bit as the sacrificial lamb! That piece is donated to convert the rest of it into heat that heats your home. The wetter the wood, the bigger the piece you need to cut off, and depending on where you get your wood from, this isn't just a slither, this can be up to half the piece of wood!
So now you have a bit of background, let's revisit this idea that kiln dried burns away quicker!
Well, it's not necessarily untrue, but that's not a bad thing! Less water means it gets going quicker. The water isn't holding things back so it starts putting out heat sooner. The vast majority of that time difference, is simply the wetter piece to start putting out proper heat! So all your really gaining in time is a period where the wood is sitting in the fire, doing nothing but sucking the heat out the last piece burning!
Now there's an interesting idea! If the last piece is having heaps of it's energy absorbed by the new piece, can you still count that time? Well if all you care about is whether you can see a piece of wood still existing in the fireplace, then yes, sure! But if you care about how long the piece of wood is being useful to heat your home, then not really, because the output of the log-burner reduces!
So here's the key message here, the question actually needs to be
"how long is this wood raising or maintaining the temperature of my room?"
For wetter wood, the clock starts later because it just takes longer to get going, and the clock stops earlier, because it needs to dedicate time to the next piece!
So yes the wetter wood exists for longer in the fireplace, but the drier piece spends more time heating your room, and here is the real kicker - during the time it is heating your room - let's call it the useful burn time - it reaches a much higher intensity. So the gain in temperature in the room is greater, and it's doing so for longer!
Put simply, with drier wood, you do not need to use as many pieces! For some that is counter intuitive but for most of our customers that's why they keep coming back!
Bonus Rant - Overnight Burns
What about wanting to burn overnight? Maybe a wetter piece has an advantage here with a delayed start and prolonged finish (with no additional piece added at the end when everyone's asleep)?
Sorry, once again, this isn't helping!
The kiln dry wood starts immediately raising the temperature the room. The air, the walls, the furniture, everything is absorbing heat. Once the fire starts running out in the early hours of the morning, the room starts falling in temperature, but it's falling from at a higher point, the heat in the room creates a more steady drop and even though the fire might be out, the room take hours for all of that high intensity heat creating a warmer room in the morning.
The wetter wood has a delayed start - sounds good right? Well not really, because while it's trying to heat up the temperature of the room is dropping or stagnant. By the time it starts putting out heat, it's already behind. The air, walls and furniture are all comparatively colder. Because it burns with less intensity, it takes longer just to get back to the temperature it was at 10:00am! By this point, the kiln dried is miles ahead. By the early hours of the morning the wetter wood has been through it's intense period and is now in it's final hour. It's kiln dried counterpart may have just finished about now but it doesn't matter because the room temperature is so far behind. This last hour is low intensity fade to black which slightly closes the gap, but by 6:00am in the morning, the room is still a few degrees lower. That could be the difference between say 16C vs 13-14C when you go to get things up and running again!
So what's the key takeaway here!
- Moisture content matters! It's not just about being wet or dry, it's about how wet, or how dry! Every bit counts
- The cost per cubic metre can be misleading as to the real value! You really want to know the cost of heating your home for the season, and that comes down to what your actually getting for what you spend.
- This is why we pioneered kiln drying, we invest into the wood we sell. We spend more on it so that each piece does more work. We truly believe our firewood is the best value in the country!