Stainless steel vent

[hubert_s]

I just closed the dome on my Pompeii oven and it is time to get serious about fabricating a vent. I plan to have a stainless steel vent fabricated and have a few questions.

1. What type stainless should be used? Is 304 ok?
2. What thickness should I use?
3. What angle should I use for the funnel part? I was thinking 45 degrees.
4. What is the best way to fasten to the brick walls and is there some type of caulk that can be used to seal the gaps?
5. Should I wrap the whole thing in insulation after installation? I plan on enclosing the oven when I'm done.

Any suggestions would be greatly appreciated.

[UtahBeehiver]

Re: Stainless steel vent

HB,

304 is the lowest grade of SS and could possibly rust especially if you are in an area where chlorides are present, IE by the ocean. You see 304 a lot on appliances since it is easier to stamp and form. I guess it is up to you and the pocket book but your vent will be a visual focal point of your oven. Ideally 316 would be better. IMHO

Just read the rest of your questions so ignore my focal point comment.
Tapcons will work for fastening
Should use a high temp "refractory" caulk to seal especially since enclosing (I am not sure the silicon caulks go high enough for you vent temps.
Insulation of the vent for oven heat loss no, insulation of the vent for fire protection on your enclosure yes.

Again just my opinion.

[hubert_s]

Re: Stainless steel vent

Russel,

thanks for your comments. I'm not close to the sea, but I think I will go with 316 nonetheless.

I am wondering what thickness I need. The Duratech chimney pipe has 0.02" inner wall thickness and they use 430 stainless. I feel like 0.02" would be too thin for the vent. I think I will use 22 gauge at the minimum. If anybody has build a stainless vent, I would appreciate if you could let me know that you used and how it held up.

[GianniFocaccia]

Re: Stainless steel vent

Hi Hubert,

I wanted a more substantial single-walled that would never have to be replaced, so I had one fabricated out of 3/16" (16g) 413 stainless. The dimensions are 34x7x7". Cost of materials and welding was $180.

In addition to the flue being thick, my other requirement was it needed to relieve my entryway of any weight on it. My entryway vault is a hemispherical arch, hence there is no buttressing. The flue weighed in at 34lbs.

I had tabs welded on so I could suspend the flue via insulating firebricks, and rest entirely on the frame. The flue makes contact with the brick vent, but bears none of its weight. I used rockwool insulating caulk (2100F)to seal the IFB that sits on top of the vent and the outside of the flue where it meets the vent. The entire length of the flue is insulated with ceramic fiber blanket.

So far, the 7" flue works like a champ. After a full night of pizza-making, the flue tabs do not transfer enough heat to the IFB to make them more than luke warm. Along with the vent, the flue length totals 42". It is insulated with ceramic fiber.

HTH,

John

[hubert_s]

Re: Stainless steel vent

Hi John,

that is a pretty nice setup. Is it 3/16" or 16g?

My chimney goes through the patio roof and then the roof overhang of the second story. I have a Duratech chimney in place and just ordered the elbow kit and additional pipe lengths to bring the chimney down to the right spot. I plan to strap everything to the rafters of the patio roof to carry the weight. Once I know where exactly the chimney ends up, I will have the vent fabricated. That is probably two weeks out, so I have some time to think about it.

I think it is going to be tricky to get everything assembled since the top section of chimney is already in place and the DuraTech system is pretty rigid and does not allow much wiggle room. I think I will probably have to build the side walls that the vent sits on last. I'll post to my build thread once I figure it out...

[hubert_s]

Re: Stainless steel vent

John,

I tried to look up 413 stainless steel and cannot find technical data. Did you mean 430?

Thanks,

Hubert.

[GianniFocaccia]

Re: Stainless steel vent

Hubert,

My bad: My stainless entryway floor is 3/16". The flue is 1/8", but I can't find my receipt to confirm what kind of SS it is.

I like your idea of hanging the weight of your chimney on the patio roof. It might be a good idea to install as much as you can prior to having the vent built in order to accommodate the positioning of the bottom of the flue.

I would have preferred an 8" square flue, but had to go with 7" to accommodate a trapezoidal-shaped vent. The vent was constructed to match up perfectly with the inside of the flue. Luckily, the 7x7" area was not that much difference (49" vs 50") than a round 8", and my slightly smaller (39") oven breathes great.

FWIW, here's a pic of how the vent mates with the flue.

John

[hubert_s]

Re: Stainless steel vent

John,

That it is a great picture, took me a second to figure out what it is. I plan to have the complete chimney in place before getting the vent fabricated. Since the chimney is all twist-lock and the top is already in place, my thought is to build the sidewalls of the entry last to make everything fit. I should have the chimney components early next week and hope that everything will become clear when the chimney is in place.

I had planned for a heat break in the floor and was going to use thin gauge SS to wrap some Insblock-19. I am now thinking about taking it one step further and putting the insulation against the entire arch and wrapping it in SS. Not sure if anybody has done that before. I have not been on the forum for very long and my search has not turned up anything. I think it would be easier to get a door to seal against smooth steel vs. my not so even brickwork around the arch.

When I started this, I thought building the dome was the hard part. It now seems like that's the easy part!

[GianniFocaccia]

Re: Stainless steel vent

Hubert,

My thoughts are these: Dome/entryway and floor heatbreak: good. Thin stainless steel: bad. With the exhaust temps these ovens produce, thin SS will warp pretty quickly. A number of builders (including me) feel that the rate of heat transfer, especially lower on the dome, is rather slow and incomplete. A previous builder here (I forget who) did use a hemispherical SS strip as a heatbreak, but a 1/4" gap between oven and entryway bricks will do nicely.

Same here: I thought the dome was the hard part until I tackled a flared entryway with different-sized arches in the front and back. No matter: whatever you're faced with you'll figure out a way to get 'er done.

[hubert_s]

Re: Stainless steel vent

John,

thank you for your suggestions. What should I fill the 1/4" gap with if I do not use the SS wrapped insulation?

I have looked at pictures of the FB Artigiano vent in the installation manual, and it seems to be made from spot welded sheet metal. I called FB and they are going to let me know what thickness the metal is. I am concerned about warping. I was planning to encase the vent in Insblock-19 and put bracing behind that on the long side of the vent, but I am not sure if that would eliminate warping issues.

As a side not, the 360 degree swivel feature on the DuraTech elbows is only on one side of the elbow and will only work if you build the chimney from the bottom up, but there is no way to swivel if you connect to a chimney that is already in the ceiling. I will have to carefully loosen the strap that holds the stack and rotate the entire chimney to get it to align. Not looking forward to that.

[GianniFocaccia]

Re: Stainless steel vent

When I built my entryway, I tapered the inner arch so that the inside of each brick made contact with the oven arch, but the outside of each brick left a 1/4" gap. This was done to insure minimum contact between oven and entryway. I covered the gap with rockwool caulk and so far, it works great. I have closed the oven following a 750F pizza session and found it 475F the following day at 3:30pm.

My external hard drive (with all my oven construction and design pics) just went south yesterday. If I can get it functioning, I'll add a pic of the caulk, including the Sketchup drawing of the tapered entryway brick design.

Edit: You can see the actual gap in the oven pic listed here in post #4.

[hubert_s]

Re: Stainless steel vent

Sorry to hear about your hard drive. I hope you can recover the data.

I am a bit torn. I thought the insulation board encased in stainless steel around the oven opening would be really nice and allow me to have a wide entry with enough room to leave the door on the side when baking. Plus, the door would probably seal a lot better against stainless than against the slightly uneven entry bricks. Unless the stainless steel warps...

[GianniFocaccia]

Re: Stainless steel vent

You know, that's your call. I too went with a number of newish designs (soapstone floor, angled arch bricks, twisted-brick entryway, etc) and feel my oven offers improvements in some areas. Just beware that all steel thicknesses warp over time.

[hubert_s]

Re: Stainless steel vent

I think I will skip the insulation board around the opening and use a 1/4" gap like you did. I googled rockwool caulk and found a number of different products, but really don't know which one is the right stuff. Do you remember the brand and product name?

As far as the vent, I am thinking about building a frame out of 1/2" or 3/4" stainless steel tubing to weld the sheet metal to. This should give the sheet metal more rigidity and hopefully limit the amount of warping.

I will attempt to turn the chimney to the correct angle on Friday and then take measurements for vent fabrication.

[GianniFocaccia]

Re: Stainless steel vent

Kaowool makes a CF caulk, but the local refractory supplier carried Inswool, an ANH Product. It was easy to install and dried beautifully. I would use it again. It was $16 for the tube in the pic.

Rather than sheet metal (prone to rust), why don't you fabricate one out of stainless? Once you get your flue in place you can design whatever trapezoidal dimensions you need.