Temperature Variations


 
R

Ron Hunter

TVWBB Member
Regarding these boards, most of the time temps are used - it's the lid temp. In the modifications area I reviewed the Excel files that show the temp deviations. I also read from some posts that your deviation is just a few degrees.

Shouldn't the variations between the lid, top grate and bottom grate temps depend on the bottom vents? For instance, if the bottom vents are 100% open, that should mean more airflow out the top vent and door. But if the bottoms vents are less than 100%, the airflow is less. Meaning the volume of hot air thru the top and door should be less.

Bottom line - wide open vents - more temp variation between lid and grates; vents tamped down - less airflow - results in a smaller variation between lid and grates.

1. Does this sound reasonable?
2. For you who check temps at different levels, what have you found - or did you not consider the effect of the change in airflow?
 
I understand what you’re saying and there’s probably some validity to the “higher volume of air = greater temperature differential” between the lid and lower grate. Generally speaking, though, wide-open vents will create a higher temperature in the WSM and I’m not sure anyone’s measured the difference between the 3 levels with temps in the 300’s. The general consensus I’ve read about temperature differentials is that initially, the lid will read higher than the top grate, which reads higher than the lower grate. The temps have a tendency to equal out over time as the heat fills the WSM from the top down and things settle in for the long run. I will agree with you in that if the airflow were greater, the temps probably would not equal out as much.

Bill
 
1st let me state that I'm no physicist. My take on this, and it's less than .02, is that the design of the unit most likely was to move the minimum amount of air thru in order to save fuel and easily control temps. I imagine the vents control the amount of oxygen to the fire but don't have an appreciable affect on the movement of air THRU the unit. That being said, once you have a stable fire, then regardless of the vent settings, the temp difference between the 3 mentioned areas would generally fall into the same range. For example, regardless of your target temp, the temp differential between top vent and top grate should always be around 20-25*.
 
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Paul K:
1st let me state that I'm no physicist. My take on this, and it's less than .02, is that the design of the unit most likely was to move the minimum amount of air thru in order to save fuel and easily control temps. I imagine the vents control the amount of oxygen to the fire but don't have an appreciable affect on the movement of air THRU the unit. That being said, once you have a stable fire, then regardless of the vent settings, the temp difference between the 3 mentioned areas would generally fall into the same range. For example, regardless of your target temp, the temp differential between top vent and top grate should always be around 20-25*. </div></BLOCKQUOTE>

Paul, are you saying if you are shooting for 230° at the top grate you should target 250-255 at the lid? My lid runs around 10° higher than the top grate--at least it did last week.
 
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