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[GatorDave]

How much does raising and lowering the chimney hat affect grill temps.  I'm aware I will need to be careful of causing a flame out, but does raising and lowering help even out temps in the grill?  In my mind, closing it down some will, but I know some of you will have experience and wisdom to impart.

[triplebq]

I personally haven't done anything to my chimney hat on any unit I have ever owned. I personally haven't seen or had a reason to mess with it.

This is just one person's view though.

[slaga]

I personally consider the cap on the chimney a device to prevent water from entering my pit through the chimney. I have never used it to control the temperature or even out temps in the grill. That said, the manual for my Copperhead 5 states, "NOTE: Adjust the chimney cap to affect the airflow inside the main grill. If cooking at low temperature, keep the cap more open." I just leave it wide open all of the time. As a matter of fact, I remove it when I cook and just set it back on when I am done cooking.

From an engineering perspective, if you increase the temperature of air, it will expand. Looking at the table below I took from www.engineeringtoolbox.com, a 150 degree (F) rise in temperature equates to about a 37% to 38% increase in volume. By volume, you will have about 37% to 38% more air leaving the chimney than the fan blew into the grill if you are seeing a 150 degree temperature rise over ambient. The more you heat the air, the more it expands. If you restrict the air flow, it will find the path of least resistance, be it through the auger tube, around the doors, etc. I personally see no purpose in trying to push air through any other hole other than the chimney so I never try to restrict the flow through the chimney, but that is just my opinion.

Edit below:
In the picture below they are talking about heating the air externally, meaning the air is air before and after it is heated. In pellet grills, a good portion of the air entering the grill is converted from mostly nitrogen and oxygen to CO2 and water through the combustion process. It is not an apples to apples comparison but it does get the point across that by volume, considerably more air leaves the grill than enters.

[GatorDave]

I personally consider the cap on the chimney a device to prevent water from entering my pit through the chimney. I have never used it to control the temperature or even out temps in the grill. That said, the manual for my Copperhead 5 states, "NOTE: Adjust the chimney cap to affect the airflow inside the main grill. If cooking at low temperature, keep the cap more open." I just leave it wide open all of the time. As a matter of fact, I remove it when I cook and just set it back on when I am done cooking.

From an engineering perspective, if you increase the temperature of air, it will expand. Looking at the table below I took from www.engineeringtoolbox.com, a 150 degree (F) rise in temperature equates to about a 37% to 38% increase in volume. By volume, you will have about 37% to 38% more air leaving the chimney than the fan blew into the grill if you are seeing a 150 degree temperature rise over ambient. The more you heat the air, the more it expands. If you restrict the air flow, it will find the path of least resistance, be it through the auger tube, around the doors, etc. I personally see no purpose in trying to push air through any other hole other than the chimney so I never try to restrict the flow through the chimney, but that is just my opinion.

Edit below:
In the picture below they are talking about heating the air externally, meaning the air is air before and after it is heated. In pellet grills, a good portion of the air entering the grill is converted from mostly nitrogen and oxygen to CO2 and water through the combustion process. It is not an apples to apples comparison but it does get the point across that by volume, considerably more air leaves the grill than enters.

This isn't the route I would normally take, as there are potential problems with it, but I think with the new diffuser plate and a little adjustment on the chimney I will get close enough to the even temperatures I'm looking for.  I really want to test it this weekend, but I have a wedding to go to out of town.

[slaga]

I personally consider the cap on the chimney a device to prevent water from entering my pit through the chimney. I...

This isn't the route I would normally take, as there are potential problems with it, but I think with the new diffuser plate and a little adjustment on the chimney I will get close enough to the even temperatures I'm looking for.  I really want to test it this weekend, but I have a wedding to go to out of town.

Potential problems? Can you please explain? (I value and respect a difference of opinion)

[GatorDave]

I personally consider the cap on the chimney a device to prevent water from entering my pit through the chimney. I...

This isn't the route I would normally take, as there are potential problems with it, but I think with the new diffuser plate and a little adjustment on the chimney I will get close enough to the even temperatures I'm looking for.  I really want to test it this weekend, but I have a wedding to go to out of town.

Potential problems? Can you please explain? (I value and respect a difference of opinion)

flame out is the big one.  The other being back burning, which actually won't be an issue with my unit.

[imahawki]

I think it makes zero difference and some brands don't eve have adjustable caps.  They're just fixed.  This isn't a charcoal grill or stick burner where you control intake and exhaust to get the right temp.  You have a fan driven controller managed temp system in a pellet grill.  If its adjustable e.g. the GMG caps, set it to open a couple inches.  I'd be stunned if you could prove with empirical measurements that it impacts temp.

[GatorDave]

I think it makes zero difference and some brands don't eve have adjustable caps.  They're just fixed.  This isn't a charcoal grill or stick burner where you control intake and exhaust to get the right temp.  You have a fan driven controller managed temp system in a pellet grill.  If its adjustable e.g. the GMG caps, set it to open a couple inches.  I'd be stunned if you could prove with empirical measurements that it impacts temp.

I'm not trying to change the temps, only even them out throughout the grill.  Slowing the escape of hot air seems like it should have at least a little bit of an effect on that.  In my mind it should work a bit, but I have been very wrong before.

[imahawki]

Ah, that is an important distinction.  I'm still not sure I buy it and lots of junk science is founded on "it seems like it would make sense that..."  You are free to try it.  I would think a thermal mass like a water pan or bricks below the drip tray might be more effective in evening out temps.

[GatorDave]

Ah, that is an important distinction.  I'm still not sure I buy it and lots of junk science is founded on "it seems like it would make sense that..."  You are free to try it.  I would think a thermal mass like a water pan or bricks below the drip tray might be more effective in evening out temps.

If only.  I'm seeing temperature differences of 60 degrees from the back to the front.  I've actually made a different heat deflector that should take care of most of that, so closing up the chimney was just an idea to tweak them a bit more.

[imahawki]

What smoker?  Those are some pretty big swings.

[GatorDave]

What smoker?  Those are some pretty big swings.

https://pelletfan.com/index.php?topic=2734.0

[slaga]

I personally consider the cap on the chimney a device to prevent water from entering my pit through the chimney. I...

This isn't the route I would normally take, as there are potential problems with it, but I think with the new diffuser plate and a little adjustment on the chimney I will get close enough to the even temperatures I'm looking for.  I really want to test it this weekend, but I have a wedding to go to out of town.

Potential problems? Can you please explain? (I value and respect a difference of opinion)

flame out is the big one.  The other being back burning, which actually won't be an issue with my unit.

(Sincerely) Good luck with your endeavors. I have suffered none of your potential problems on my 3 pellet grills when the chimney cap has been fully open, removed or when the pellet grill did not have a chimney cap to begin with. I am interested in the solution you arrive at that makes this grill work for you.

Have you considered a tuner plate type design below the grate where the larger holes are at the front and smaller holes near the back like the picture below? Maybe even have the front corners mitered at a 45 degree angle to ensure you get more heat flow at the front corners than anywhere else? Just a suggestion.

[slaga]

What smoker?  Those are some pretty big swings.

The issue is not with temp swing... The front corners are roughly 50-60 degrees cooler when the rear middle of his grill is at 250.

[GatorDave]

I personally consider the cap on the chimney a device to prevent water from entering my pit through the chimney. I...

This isn't the route I would normally take, as there are potential problems with it, but I think with the new diffuser plate and a little adjustment on the chimney I will get close enough to the even temperatures I'm looking for.  I really want to test it this weekend, but I have a wedding to go to out of town.

Potential problems? Can you please explain? (I value and respect a difference of opinion)

flame out is the big one.  The other being back burning, which actually won't be an issue with my unit.

(Sincerely) Good luck with your endeavors. I have suffered none of your potential problems on my 3 pellet grills when the chimney cap has been fully open, removed or when the pellet grill did not have a chimney cap to begin with. I am interested in the solution you arrive at that makes this grill work for you.

Have you considered a tuner plate type design below the grate where the larger holes are at the front and smaller holes near the back like the picture below? Maybe even have the front corners mitered at a 45 degree angle to ensure you get more heat flow at the front corners that anywhere else? Just a suggestion.

That's essentially what I'm making, minus the holes.  I'm building a diffuser plate that will sit above the OEM plate.  It's going to have a slight rise to it (2" per foot) and move the heat to the front, then it can flow to the back and out the chimney.  I think doing that, with a slight restriction on chimney will give me the results I'm looking for.  I knew going in that I could have problems with this pit, since I had almost know information on it.  If I can get the temps regulated, I will be a very happy camper with my purchase.