Flue transition plate

[P3 Stoaker]

G'day All,
I have been looking for a flue transition plate for some time and I've asked on the Forum before without luck. I'm still unable to find a product I'm confident will perform the Job.
What I'm after is a transition plate that can attach to a horizontal brick surface, above the vent arch and allow for the use of an 8" flue. I've seen them on this forum numerous times. Do you know where they are sold, preferably in Australia?
Regards

[UtahBeehiver]

Duravent, Selkirt, Metalbestos are some but they are specific to their double wall vents. They are shown in their catalogs. You don't say what type of 8" vent you are using, IE single wall, double wall, brand or such so kind of hard to answer you question.

[P3 Stoaker]

G'day Russell,
Many thanks for your reply. Do you have any recommendations as to what way to flue, single skin, double layer etc. My 42 inch oven will be outside and I'm planning on raising the flue vent only as high as required to establish enough horizontal area for the transition plate. Having said that I'm quite flexible as to which way to go. I am assuming a transition plate for even a single skin flue will mean around a 10 inch square plate. I expect a transition plate for a double skin flue would be even bigger and I do wonder how that would go with a somewhat limited surface area available, given the longer the transition plate the longer the entry needs to be.
Many thanks
Greg

[UtahBeehiver]

It is all budget, availability, personal taste driven on vent choice. The actual dimensions anchor plates are in the catalogs. The vent chamber needs to have at least the same square area of the square area of the chimney ID. So you may have to make a vent chamber transition from rectangle to square of round. Look are various builds to get options. On a 42" you will need an 8" ID chimney.

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[P3 Stoaker]

G'day Russell,
Apologies for the delayed, but appreciative reply, thanks for the info. I've looked around and found this photo which is similar to how I intend to use the top plate. With an outer flue sitting over the little riser on the base plate, then the sides turned down over the brick edge I hope any water, rain, is diverted away from running through the vent and ending up on the oven floor. These plates are reasonably priced to have custom made here. I'm considering not even screwing/bolting the plate down as I have a beam above and can manufacture a bracket to hold the flue, in place and preventing it from rising. I'll use silicone/fibre tape on the upper surface of the bricks for the plate to sit on and seal.
Only feature I'm yet to finalise is if I need the gap between flu's vented at the bottom, and if so how to allow air but not water in ??
I'm getting there slowly, just sorting out how to close the dome off, another full row will leave a gap a little big for a single plug, I might go with a bigger plug in 2 halves.
Regards. Greg

[david s]

If your oven is outside I don’t think there’s any requirement for a double flue, although it appears that you have a timber structure above it. In which case the flue should be at least 50 mm away from any flammable material.You will need to check your State regualtions for their requirements as they vary.
Apart from anchor plates being pricey they introduce other problems. Firstly the plate that is to be fixed to the brick or casting is often too big and requires trimming down. Secondly, drilling into brick or refractory is inviting cracking. Lastly this cracking is further compounded by any metal fixing that will expand in the hole well before the refractory or brick that surrounds it because of its higher conductivity.
Just as the flue pipe and anchor plate made of plated or galvanised steel will corrode in that position, so do fixings, so don’t use anything other than stainless. I’ve also found that high temperature silicon fails in that position (at least it does in my design although 150mm higher it’s ok, just) For these reasons I don’t use anchor plates in my design.

[P3 Stoaker]

G'day David,
Many thanks for your reply. Yes my oven is outside but I can say if I had my time again I'd design a roof over it.
Given it is outside I'm keen to design things so water cannot run down the flue and inside the vent to the floor. Do you think an anchor plate, made to fit and turn down an inch or so around the edges, not bolted/screwed down and sitting on some fibre heatproof insulation tape to seal would eliminate most of the concerns you've experienced/seen? if not what method are you using?
Regards

[david s]

Hi Greg,

I don't use an anchor plate because of the afore-mentioned reasons. I cut three tabs in the base of the pipe and bend them out at 90 degrees to allow the pipe to fit. This allows the pipe to expand and contract safely. It is surrounded by 6:1 vermicrete which is firm enough to hold it in position but weak enough to accomodate some expansion. My design incorporates a breather that allows moisture to escape between two terra cotta caps that I manufacture, but that's more complex so simply rendering the outer shell up to the pipe, wrapped in some box cardboard which when removed will leave a gap approx 5mm thick which when removed can be filled with high temp silicone. Water entry and cracks around the pipe is common unless addressed. The attached pics should tell the story.

This may help you or you may come up with another solution.

[P3 Stoaker]

G'day David, thanks for the reply. Sounds like you are well sorted with your design, I detect you've built a few of these !!
I was at one stage somewhat confident that a plate, made to order as seen above in post no 6, just sitting there, no bolts but secured to an above structure so it cannot move would address most issues. I might have to reconsider given your experienced comments, which of course is invaluable. The plate design would account for mounting (nil fittings to brick) and expansion but I'm still weary given the concerns raised.
I've only just closed the dome yesterday so I have a bit to consider and sort out before I proceed further.
Kind Regards
Greg