Heat Spike and Fan Question


 

Bob Ivey

TVWBB Emerald Member
We did fathers day on Saturday so I did an overnight on Friday night and was now able to sleep. All went well but I did notice a minor problem and am wondering if the fan is the problem. When I hit the stall, I went out and foiled both the brisket (top rack) and pork butte (lower rack) and put the lid back on. Set temp was 235* and after replacing the lid I watched the display on my iPad and saw the pit spike to above 250*. The graph showed the temp go down when lid came off and then spike high for a while. The temp did come back down after a while but it seems like it should have taken less time. What I am wondering is if the fan is the problem? What I am thinking is this. Even though the fan shuts off when the set temp is reached, the temp still rises. Since the parts list fan does not have a baffle to shut off airflow, is the fan still allowing air to stoke the fire and fuel the spike. Other than the top vent (about 50%), the bottom vents are closed with the exception of the bottom fan. The center section and door are equipped with nomex. There is still a slight amount of smoke coming out of the door but not much. Will deal with this soon. I am wondering if my idea of the fan being the problem, would the Auber fan that is equipped with an automatic baffle help stop the temp spike. Twice more in the morning I had to pull the lid and noticed the same spike activity. Any thoughts?

TIA

Overall, the HM is GREAT!! Untill the spikes, temp was held within a degree or two for hours.
 
Yeah the real key to HeaterMeter working properly is that the fire has to go out if the fan isn't running, and it shouldn't ever spike more that 10 degrees over the setpoint in an extreme case. If you're getting too much air in, the temperature can spike on it's own (the fan is off the whole time) or ride high for a really long time after you open the lid (long = 20+ minutes). If you can't choke it off enough using the vents, then you can try making your own baffle or buy one of the pre-made fans with integrated baffle.
 
The other thing to consider is how you have your fuel setup. If you have a bge and are using a mix of coals with wood chunk and you open the lid long enough, you can ignite a wood chunk that will set off a heat spike. It can take a little while to recover from this.
 
Tom, it is a WSM22. There is a little leakage at the door but not really anywhere else. Other than where the fan is installed, the other two lower vents were closed. The upper vent was at about 50%. Both center section joints have nomex to seal them. I am thinking that an Auber fan might help since it has an automatic damper so the air is closed when the fan is off. The WSM had been very stable until I had to remove the lid to foil the brisket and the butte. After that, It took a while to deal with the spike.
 
I have about 80% of the fan intake covered with foil tape on my Big Steel Keg, in addition to every edge of the lower vent being sealed with tape. Without that, natural leakage keeps me above 225*....
 
Even on my Egg, if I open the top vent more than a toothpick-width, the temperature starts getting tough to control at 225F. I was never able to build an effective damper on the fan, but depending on the orientation of your fan mount bracket, one could possibly tape a piece of cardboard that flops over the hole when the fan is off that provides some amount of restriction. I tried this myself but because my fan doesn't tilt back at all, it didn't really close all the way.
 
I have found that I need to prepare to open the lid by disconnecting the fan so it doesn't run even if controller calls for it when the lid is lifted and I shut the top vent completely for a few minutes before lifting the lid. Lifting gives the cooker a big shot of oxygen so be as quick as possible. I use Aubers and Gurus and one team member has the IQ110. Same with all of them.
 
ProTip: You can press left on the HeaterMeter directional control before lifting the lid and it won't run the fan for the next 4 minutes (configurable) as long as the temperature dips within the next 30 seconds. Doesn't work if you do it a few minutes in advance though, sorry. I hit the button then open 'er up and take the food out to do my business to minimize that oxygen burst it gets.
 
I experienced this same issue with my WSM 22.5 on it's first run two weeks ago. I use lump and that stuff reacts to oxygen VERY quickly. One little trick that I did discover is that if I lift the lid and don't turn it over, keeping the hot air trapped in the lid, and put it back on it took a lot less time for the smoker to settle back down.

I had to tape over one side of the fan completely to keep things from getting out of control on that windy day.
 

 

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