Ordering firewood

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A rough formula based on log burning stove requirements has been calculated but its not exact because we use open fires not enclosed stoves, and if its warm and dry hardly anyone has fires on all day, but if its wet and/or cold their fires are going all the time. Also if the wood is dry and seasoned it burns quicker but provides more heat so you actually use less, it follows that if the wood is wet/green then you need more….

Assume that a full day is 9 AM till 7 PM, i.e. 10 hours. Some people will have fires on longer some shorter. A 10 hr average seems practical if the weather is bad and the fires need to be on all the time.

1 fire will use between 1.0 to 1.5kg of dry wood per hour. Again very variable as it depends on the condition of the wood and wind conditions. The reasonable average is 1.25kg of dry wood per hour.

So on average each fire will use 1.25kg x 10 hrs = 12.5kg dry wood per day.

You then need to calculate or guess the number of fires you will have. The average major now has 70 tents with say 50% with a fire = 35 fires. Therefore wood required per day = 12.5 kg x 35 fires = 437.5 kg Add say 10% extra just in case, then round up to nearest 50kg.

We usually ask clients for half a tonne = 500 kg per day for a major. However we also tell clients that we will review matters at the end of day 1. So if they deliver a full tonne for a two day show and there isn’t any left by tea time on Saturday we ask if they can get another ¼ ton delivered Sunday morning,

For smaller events you can work out rough volumes from the above formula. Say half the figures for a medium = 250kg per day, and half again for a minor = 125kg per day.

This assumes use for small camp type fires only. If there is going to be a late night larger communal fire / bonfire then you need to order wood specifically for that.

Main problem we have is that people squirrel wood away in case they need it so we have had lots of events where we have had ask the client for more wood at the end of day 1, only to find that half the wood pile is returned at the end of the event, or worse still the camp site is left with impromptu jenga stacks of wood all over the place.

Also note that wood is best purchased by volume, not weight (despite the above info being in weights). The issue here is that wood is heavier when wet, so fresh cut wood will be heavier than drier seasoned wood. Most commercial firewood is kiln dried whilst most bulk timber is “as it comes” and if stored outside it is likely to be wet. If you buy wet wood by weight then you are actually paying for the water in the wood. Wood densities vary considerably by species but as a guide :-

Dry hardwood is around 600 kg/m3 except willow which is around 400 kg/m3, whilst softwood is anything between 400-500 kg/m3.

Wet wood will be heavier but it depends on how wet. Fresh cut the general rule of thumb is that the wood will be 50% heavier.

Fresh cut hardwoods are around 900 kg/m3 but can be as high as 1100 kg/m3. Softwood will be around 600-750 kg/m3 as felled. Most wood will have lost some moisture and therefore be lighter than these figures by the time its delivered. These figures are at the time the tree was felled. As soon as its logged it starts to loose moisture and weight, and unless its perfectly dry and seasoned there is no way to tell how wet the wood is without proper testing.

Addendum :

A builders 1 tonne sling bag measuring 90x90x90 cm = approx 1 cubic metre in absolute volume but will only hold about 1/2 cubic metre of wood due to air spaces between the logs.

On the basis of the above information, we require about 500kg or wood per day, but lets increase that to say 600kg being the dry weight of a cubic metre of hardwood. So we need approx. 1 cubic metre of dry hardwood per day.

If 1 tonne sling bags only hold 1/2 cubic metre of wood, we need 2 no. 1 tonne sling bags of dry loose logs per day for a major with approx 70 tents. You can vary the amount needed by reference to the actual number of tents expected.