Cold Oven Draw Test

[stonecutter]

I shot a quick video showing how sizing the throat opening correctly will create a very strong draw in a cold oven. It's not for a brag...there has been some discussion about this lately, and it visibly illustrates how strong the draw can be, even with a stone cold flue. This is the second video....I uploaded it first by mistake. The first video should be up in an hour or so..they take forever to upload on Youtube. That one shows the start of the fire in the back of the oven...not under the throat, and no pre-heating the flue. Ambient outside temperature was 52 degrees, and masonry is usualy cooler. I don't own an IR gun as of now, so how cool the masonry was, I don't know exactly.

Anyway, this video was shot within a minute after the first, and there was no continuous fire...the flue and throat were still barely warm. Note the large particles of ash getting sucked up the flue, and the way the smoke is drawn up immediately after passing the outer face of the oven arch.

I had mentioned in a previous post that this throat is 10.75" across....it is 5" wide.

Cold Oven Draw Test

We have been using this oven since July, and I have never had any smoke make it past the granite. I'm going to make another video soon, to try and see how far I can go before I get smoke roll out.

[stonecutter]

Re: Cold Oven Draw Test

Cold Oven Draw Test 1


Initial fire up...some cardboard and ripped newspaper. The angle doesn't show the draw very well, but you can see how far back the fire was started, and the lack of staining on the granite.

[wotavidone]

Re: Cold Oven Draw Test

Very good. I've just been out and measured mine, which was sort of done by eye. "Yeah, that looks about right."
Guess what? "My yeah that'll be about right" is 12 inches by 5 inches.
Reckon that'll be about right?
Mine does have a bit of staining on the front, but I put this down to lighting the thing with the flaming wind blasting around me, as usual. As I wrote in previous posts, I have a thing that looks like a blast door, but is actually used as a wind excluder.
As I type, the wind is gusting to 22 knots at the airport, according to willy weather.
The snapper fishing seasonal closure ended at mid-day on the 15th, and I haven't yet had one night where the wind is calm enough to launch the boat and get amongst them.
At least the change is coming through and the temperature has dropped from 108 to 88F.

[stonecutter]

Re: Cold Oven Draw Test

"That's about right"is pretty close to what I had to do for all the ovens I built, except for the Pompeii I built at my other home....that was the only time I used any plans for oven construction. I don't remember reading anything about scaling the throat opening, though. As mentioned before, after building many Fp's and such, sizing throats has become more instinctive for me. What I am trying to establish is some solid numbers that new builders can trust, and that are reliable. For some, seeing smoke stains on the front of the oven finishes is no big deal, but it is for others. At least this data might be of some use for those that don't want the staining.

My oven here is oriented with the opening facing the prevailing wind. We are second row off of a huge lake, and we often get windy days because of it. I am going to do another flue vid next time it's blowing. This test wasn't planned, I just thought of it as the sun was setting and I wanted to try uploading a YouTube vid.

[Toomulla]

Re: Cold Oven Draw Test

I agree regards the wind my oven also has the door facing the prevailing wind an at 33 knots last week I struggled to get the oven over 600 f until I propped the door up as a blast door

[kanoer54]

Re: Cold Oven Draw Test

I'm just the amateur taking the lead from our peers. I have a 39 inch oven with a 16 dome and a 10 inch clay tile flue. Smoke always draws right up the flue no matter what direction the wind is blowing. A lot of times I will wait til the oven is around 400F or so and then set the blast door under the outer arch, which seems to help quite a bit to accelerate the fire and oven saturation.

[stonecutter]

Re: Cold Oven Draw Test

I did another video in the rain yesterday. It was 7-10 mph with gusts up to 15 mph. This time I started the fire all the way in back of the oven, with minimal paper and damp wood.

As the video shows, the wind is forcing smoke out of the vent intermittently, during the stronger gusts...there was a steady wind in addition to that. Overall, the throat did well, as there was no continuous stream of smoke coming out of the oven. I put my hand on the oven opening (around 4-5 seconds) to show that the masonry had not warmed up significantly enough to create a good draw based on thermal property alone. This was the worst I have seen as far as losing smoke out of the vent....on calm days, it will swirl just before the granite before going up the flue if the start up is especially smokey. That will be my next video.

I think this illustrates that a draft door can be beneficial for ovens that must face strong prevailing winds or areas like were wotavidone lives....if the throat and vent cannot recover the smoke stream during gusts, or if you want to avoid staining the front of the oven because of an undersized throat.

Windy Day Draw Test. - YouTube

[Toomulla]

Re: Cold Oven Draw Test

Or buy some good cleaning compound and clean it off.

Personally I regard the smoke as a badge of honor and indicator that the WFO is used

[stonecutter]

Re: Cold Oven Draw Test

Or buy some good cleaning compound and clean it off.

Personally I regard the smoke as a badge of honor and indicator that the WFO is used

Everybody has a right to their own opinion. But that reasoning doesn't make sense to me.

[Tscarborough]

Re: Cold Oven Draw Test

I regard the output of the oven as the badge of honor, not the smoke. I saved my black brick for years just for a fireplace surround or oven so you couldn't see any stain, but as it turns out they were not needed.

[david s]

Re: Cold Oven Draw Test

if you are careful it is possible to fire the oven with no smoke escaping out the front and virtually none at the chimney. However this does require really dry wood. I was once set up at a market stall next to a woman who was selling hand knitted baby clothes. I was quite concerned about the smoke issue so when I lit the fire I started it really small and very carefully fed the fire with minimal amounts of wood as required. Using this technique i was able to produce a virtual smoke free firing from start to finish, but it takes constant monitoring. In normal practice we usually over feed the fire, which results in an excess of fuel and some smoke which is unburnt fuel. In addition if the flame is allowed to die and more fuel thrown in the oven wil lproduce a fair amount of smoke. Using the trusty blowpipe will get the flame going again quickly. Also if you preheat some wood in the entry it will burst into flame as soon as it hits the fire.

I have since added an extra flue pipe length to make my chimney on the mobile oven taller. This has proved to be an effective measure to keep smoke higher and away from other stalls.