What is the shortest logs you have been asked to supply?

[dig-dug-dan]

Oh dear. Some basic physics needs applyimg lads.

yes but cutting smaller, you get more surface area, they burn hotter adn quicker. You cannot get more energy out of a log by cutting it smaller, it just releases that energy quicker.

if I have small stuff on my 11kw, I have to shut the vents down on to stop overfiring. If I burn bigger logs, I can open the vents, and het a longer more controlled burn.

[cornish wood burner]

Oh dear. Some basic physics needs applyimg lads.

yes but cutting smaller, you get more surface area, they burn hotter adn quicker. You cannot get more energy out of a log by cutting it smaller, it just releases that energy quicker.

if I have small stuff on my 11kw, I have to shut the vents down on to stop overfiring. If I burn bigger logs, I can open the vents, and het a longer more controlled burn.

 

If you read my post I did say "same amount of heat/kg of logs". Just because you can overfire your wood burner it doesn't mean all will.

To give the same output to the room a stove with a back boiler will need to burn its fuel much quicker as the energy is shared between the water and room.

Im sure you know to achieve correct running a certain temperature needs to be achieved.

[openspaceman]

Oh dear. Some basic physics needs applyimg lads.

 

That's what Ian and I did

 

 

yes but cutting smaller, you get more surface area, they burn hotter adn quicker.

 

The flame temperature cannot exceed about 1600C but because more heat is being released the stove does get hotter and because it is hotter it dissipates more power.

 

You cannot get more energy out of a log by cutting it smaller, it just releases that energy quicker.

 

That's what we said

 

if I have small stuff on my 11kw, I have to shut the vents down on to stop overfiring. If I burn bigger logs, I can open the vents, and het a longer more controlled burn.

 

This last is an interesting one, the air supply should be related to the heat output, so burn lots of small logs will require about 6kg of air per kg of logs burned. Most wood stoves require a bit more air to eliminate unburned gases from the exhaust so typically you will supply between 50-100% excess air ( the damper the logs the higher the excess air in general). Limit the surface area by using a large log AND increasing the air supply means you are passing more excess air, which in turn means the fire is cooler but also more heat is wasted in the increased massflow up the chimney.

[dig-dug-dan]

Fair comment. We all know how our own stoves work best I guess.

my dad insisted when he had 6 inch logs, in cutting them all up into small bits so he could get more heat out of them. He was forever loading the fire up!