Montana State University

MSU Extension Forestry

How much Energy is in a Slab of Wood?

Author: Martin Twerplaques
Update: 11/05/2014

This exercise is for illustrative and educational purposes only!

All default values can be changed.


STEP 1 - Get the weight of a slab of wood (without bark)

The calculator uses "pounds" as the unit for weight, so you can convert from other units here:

oz lbs
kg lbs

STEP 2 - Calculate the energy content

The energy yield is the amount of energy that can be captured from burning wood.
Here it is expressed as BTU per pound of wood. One BTU is defined as the amount of energy required to increase the temperature of one pound of water by one degree Fahrenheit (F).

What kind of wood do you have? What is the moisture content of the wood?
Birch
Cottonwood
Cedar, Western Red
Douglas Fir
Hemlock
Pine, White
Pine, Lodgepole
Pine, Ponderosa
Spruce

If you can't measure it, here are some examples:

Kiln/Oven dry (3%)
Air dry (20%)
Green (50%)


Gross Energy Moisture Content Weight (Step 1) Energy Yield
BTU/lb % lbs BTUs
Joules
Calories
Watt hours

STEP 3 - What could you do with this energy?

You could heat water to take a shower.

To calculate for how long you could take a shower, we need two numbers:
The Temperature Rise and the Amount of Water used or Flow.

The Temperature Rise, or delta T, is the difference between the starting temperature of the water you want to heat up and the temperature you want to heat it up to.

The Flow is expressed as "gpm", gallons per minute.
The current standard for residential showerheads is 2.5 gpm, but if you have a modern water-wise showerhead that uses only 1.6 gpm, enter that number in the appropriate box ("gpm") below.
A gallon of water weighs about 8.35 pounds.

Temp in Temp out Temp rise
F F F
       
Flow Shower time
gpm or lbs/minute
minutes:seconds


You could power a lightbulb.

A 60 Watt equivalent lightbulb could burn for  
     
Incandescent (uses 60W/hr)
days:hours
Compact fluorescent (uses 13W/hr)
days:hours
LED (uses 9W/hr)
days:hours