Flue pipe

[Papa j’s]

Hi all, I’m a first time builder, I have jumped the gun and had a gather made and fitted it to my oven, the problem is, I suspect the diameter is too small after reading some posts, the oven is 40” and the gather goes to a 4” connector as the chimney with cowl and dampener i got is 4”. my question is would I be able to put a extender from 4” to 8” from the gather and continue with a new 8” chimney and flue, or would it still not work and I need to have a new gather made

[JRPizza]

Papa j, welcome to the forum. I have heard some folks say that a little restriction/venturi in a chimney "can" be beneficial, but the area of the recommended 8" pipe is just over 50 square inch whereas the area of a 4" pipe is about 12.5 square, approximately a 75% reduction in area. My guess is the door of the oven is going to be the path of least resistance and most of your venting will be out the front. Not knowing how much money you invested in having your gather made I would probably opt for having a new one made or trying to rework the one you have to have a bigger opening. If all you were going to do was attach a simple length of 8" pipe you could try it with little to loose and see how bad it smoked, but if you were going to build a more elaborate chimney you might not want to do something you had to likely tear apart.

[Papa j’s]

Thank you for the reply, I think I’m going to change it now before i go further and create an even bigger problem, do you think a 6” flue would be sufficient as I’m struggling to find 8”

[Papa j’s]

Right I’ve bit the bullet and found an 8” flue, I have 8” x 1m 316 stainless, a storm collar and an anti down draught cowl, just need to have a gather remade now, do you think this set up would be suffice

[JRPizza]

You are moving in the right direction! What actual parts you need depends on a few factors. Are you going to penetrate a roof? Do you have adjacent structures that you need to either rise above for safety or code or do you need to control heat due to proximity to combustibles?
Tell us more about what you have built, where you have built it, and what you hope it ends up looking like.

[Papa j’s]

It’s at the back of my garden away from any combustables, I’ve added photos for you

[Timothy_W]

From the photo it is not very clear how close the trees are to the stove. If close enough, then you need either a barrier or cut off branches, because from constant heating a fire can happen.

[Papa j’s]

Hi mate thanks for that, the trees are no where near, the photo was shrunk down to upload which makes it look long

[Pete C]

Hi Papa J, quick question, what is the material you are applying to the outside of the blanket insulation? Is it the final exterior coating or an insulating concrete mix? I like your idea of using the plywood form to ensure an even thickness. -Pete

[Papa j’s]

Hi Pete, it is vermiculite and cement, it’s not the final layer I will be adding either a tanking coat or render to water proof it, but it has to be completely cured before I add that as I don’t want to lock moisture inside, and then I intend to finish it with a mosaic tile once water tight, with the plywood form it worked a treat, to get the shape I used the same “indispensable tool” to mark out the shape on the plywood and then added the thickness of brick and then the thickness of blanket plus 100mm on top for the desired thickness of vermiculite I wanted, this gives you the template in the correct shape to follow