Air circulation for gas oven

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Rocketdc
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Air circulation for gas oven

Post by Rocketdc »

I'm building a 4'x8'x6' using a Carlin ezgas burner for the heat source. I've read a lot of commentary online on these oven builds and I've seen differing opinions on air circulation and exhaust.

I'm planning to install the gas burner at one of the rear corners then use a recirculating fan to move heat to the lower area of the front of the oven. Does it matter where the fan is located along the top of the oven in regards to the burner? Should it be above the burner, in the middle, at the front? Is it even necessary to have a recirculating fan on an oven this size with a gas burner?

Regarding the exhaust, is there any reason to use an exhaust fan or just create an exhaust hole at the top with a damper to adjust it? I saw one source say the exhaust fan needs to run for a few minutes before the burner is fired to clear out the oven as a safety precaution. And during operation, the fan needs to exhaust the oven 3x per minute to maximize the btu's from the burner. This is all above my pay grade. I'd rather install fans during the build than retrofit them after, but if there's no real benefit then I won't bother.
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rdj357
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Re: Air circulation for gas oven

Post by rdj357 »

I am using a recirculation fan in both of my Carlin powered ovens. I just have my blower recirculating from top to bottom. It shouldn't matter much as long as you have some air movement it will stir up the heat in an oven that size. As for exhaust, I have a power exhaust on my 8x8x20 and a passive, dampered exuaust on my 4x3x8 - both work fine and I probably didn't need the powered on the larger oven but it is nice to be able to clear out the oven after a cure of say a full load of black.
Rocketdc
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Re: Air circulation for gas oven

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rdj357 wrote: Fri Apr 28, 2023 11:10 am I am using a recirculation fan in both of my Carlin powered ovens. I just have my blower recirculating from top to bottom. It shouldn't matter much as long as you have some air movement it will stir up the heat in an oven that size. As for exhaust, I have a power exhaust on my 8x8x20 and a passive, dampered exuaust on my 4x3x8 - both work fine and I probably didn't need the powered on the larger oven but it is nice to be able to clear out the oven after a cure of say a full load of black.
:Like How did you size the blower cfm for recirculating the air? I found a few blowers that range from 100-250cfm, I'm assuming any of them would work considering my oven size is around 145cu/ft.
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Re: Air circulation for gas oven

Post by rdj357 »

I'm an HVAC guy so flew by the 'seat of my experienced pants.' I think I went with the 310 cfm heat rated Dayton 1TDV4 knowing that that I'd get plenty of air velocity out a 4"x4" opening to make it across the depth of the oven. I'm sure the ones you're looking at will work great too.
Rocketdc
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Re: Air circulation for gas oven

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rdj357 wrote: Fri Apr 28, 2023 11:55 am I'm an HVAC guy so flew by the 'seat of my experienced pants.' I think I went with the 310 cfm heat rated Dayton 1TDV4 knowing that that I'd get plenty of air velocity out a 4"x4" opening to make it across the depth of the oven. I'm sure the ones you're looking at will work great too.
That's right, I remember reading some of your posts about hvac calcs in some of the other threads! Thanks for the feedback :Like
34by151
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Re: Air circulation for gas oven

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Not sure on the exact burner you are looking at.

If its a single stage you will need an exhaust port (vent) in the oven.
Without an exhaust port its the same as blocking the outlet
You may get away with an open floor or bad door seals though plan on a vent
You can get away with no fan if you direct the incoming air up. It will circulate a exit the vent
As your pushing in hot air, a fan wont change it much unless it a very big fan
The fan is needed if you have an electric heater (radiant heat source)

If you are able to get a 2 stage burner get that for sure.
A 2 stage has an internal heat exchanger, so you can block the outlet without an bad effect
The exhaust is also external so you can plump the exhaust outside and hot air into the oven
Whit these you use a lot less fuel and can get away without a large vent but you may need a small fan

I started with a single stage gas and moved to a 2stage diesel burner
Just remember you can have too big a heat source. The faster you can get your parts up to temp the better the rest is holding a stable temp
Rocketdc
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Re: Air circulation for gas oven

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34by151 wrote: Fri Apr 28, 2023 3:02 pm Not sure on the exact burner you are looking at.

If its a single stage you will need an exhaust port (vent) in the oven.
Without an exhaust port its the same as blocking the outlet
You may get away with an open floor or bad door seals though plan on a vent
You can get away with no fan if you direct the incoming air up. It will circulate a exit the vent
As your pushing in hot air, a fan wont change it much unless it a very big fan
The fan is needed if you have an electric heater (radiant heat source)

If you are able to get a 2 stage burner get that for sure.
A 2 stage has an internal heat exchanger, so you can block the outlet without an bad effect
The exhaust is also external so you can plump the exhaust outside and hot air into the oven
Whit these you use a lot less fuel and can get away without a large vent but you may need a small fan

I started with a single stage gas and moved to a 2stage diesel burner
Just remember you can have too big a heat source. The faster you can get your parts up to temp the better the rest is holding a stable temp
This is the burner I ordered:

https://carlincombustion.com/products/e ... as-burner/
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Re: Air circulation for gas oven

Post by 34by151 »

That will do perfect, just have your PID switch it on and off
I like the MT-S over the RexC100 as it has both SSR and 3 amp relay outputs
The relay is perfect for switching your burner
I have the hot air entry in the lower left rear corner of the over with a small baffle across the back side
This direct the air up the back wall over the top and back down
The vents are on the lower right front corner
I have 2 x 65mm tubes

The you want to and need to let the air flow though the oven
This is venting gasses and air expansion as well as for the burner
You cant block the output of the burner, it needs air flow
You need to balance the size of the vent with what the burner is happy with
The biggest will be the same size as the burner outlet
If your oven was perfectly sealed this would be the size
Add leakage around the door and it can be smaller
Add an open floor smaller again to none at all as the open floor is the vent

Another note the smaller you make the vent the faster it will get to temp
Rocketdc
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Re: Air circulation for gas oven

Post by Rocketdc »

34by151 wrote: Sat Apr 29, 2023 6:16 am That will do perfect, just have your PID switch it on and off
I like the MT-S over the RexC100 as it has both SSR and 3 amp relay outputs
The relay is perfect for switching your burner
I have the hot air entry in the lower left rear corner of the over with a small baffle across the back side
This direct the air up the back wall over the top and back down
The vents are on the lower right front corner
I have 2 x 65mm tubes

The you want to and need to let the air flow though the oven
This is venting gasses and air expansion as well as for the burner
You cant block the output of the burner, it needs air flow
You need to balance the size of the vent with what the burner is happy with
The biggest will be the same size as the burner outlet
If your oven was perfectly sealed this would be the size
Add leakage around the door and it can be smaller
Add an open floor smaller again to none at all as the open floor is the vent

Another note the smaller you make the vent the faster it will get to temp
Cool, thanks! :Like
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rdj357
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Re: Air circulation for gas oven

Post by rdj357 »

Rocketdc wrote: Sat Apr 29, 2023 7:52 am
34by151 wrote: Sat Apr 29, 2023 6:16 am That will do perfect, just have your PID switch it on and off
I like the MT-S over the RexC100 as it has both SSR and 3 amp relay outputs
The relay is perfect for switching your burner
I have the hot air entry in the lower left rear corner of the over with a small baffle across the back side
This direct the air up the back wall over the top and back down
The vents are on the lower right front corner
I have 2 x 65mm tubes

The you want to and need to let the air flow though the oven
This is venting gasses and air expansion as well as for the burner
You cant block the output of the burner, it needs air flow
You need to balance the size of the vent with what the burner is happy with
The biggest will be the same size as the burner outlet
If your oven was perfectly sealed this would be the size
Add leakage around the door and it can be smaller
Add an open floor smaller again to none at all as the open floor is the vent

Another note the smaller you make the vent the faster it will get to temp
Cool, thanks! :Like
I suppose some day I should make a proper damper in my exhaust as the cardboard and duct tape is looking a little rough from the heat. :HaHa
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