New Stainless Liner

Usually no need to insulate the liner especially in an interior chimney. If the chimney is exposed on the outside of the house maybe.

Liner is sized by the height of the liner and its diameter and the BTU input. You can look up a chart on line if you know the brand of liner

If you read through some of my many posts here you'll see a pattern. However, aside from getting a level II inspection, the liner must be suitable for the class of service. A corrugated ss liner must be derated 20% plus more for offsets not including one broad radius bend at the base. I recommend a type 316Ti smoothwall ss liner which does not have to be derated and flows much better.

A listed ss liner does not 'fix' a chimney that cannot meet the minimum requirements of the listing. For instance, every listed liner is tested in a chimney that is constructed with 4" wythe walls. The flue is expected to be intact. If not, 'bad stuff' can escape into the interstitial spaces between the flue tiles and the inner face of the outer wythe wall. If acidic flues gases have escaped into this space, there will be interior deterioration not visible. The liner makes the chimney rated for a zero clearance to combustibles ONLY if you have an intact outer 4" wythe wall so yes, Mike is correct. Thx

The liner does not correct structural problems. It's a conduit or container. That's it. Ceramic flue sealants are not recognized by the codes because codes deal with new construction. You may get your local AHJ to accept it but IF the chimney is found to be sound according to a level II inspection, dry, and otherwise suitable. Ceramic liners fail if there is moisture penetration or improperly applied. They are still high mass cold chimneys not suitable for short duty cycles, such as with heating. Their durability against highly acidic condensate remains to be seen. You can take a strip of ss, run it through a machine that corrugates it then rolls it into a spiral clenching the seam as it goes and you have a 0.005 to 0.006" thick liner. You can also take that same strip and run it through a set of rollers that roll it onto a flat tube about 1/2" wide then a single layer 'joint' to the adjoining tubular roll. The rolls are 4ply but the 'seams' or valleys between than are still just single walled. Then you can roll this process to where the tubes overlap each other so you get a 4 ply round liner 0.005x4=0.002" of ss and best of all, the inner surface is smooth. This does not offer the flow restriction of a typical corrugated liner that must be derated 20%, does not hold solid or particulates very well such as creosote or fly as (wood, pellet or oil soot) and if it does it partially cleans itself by continual expansion/ contraction cycles. It also is smooth on the outside so it does not hang up going down the way corrugated liners do. They're slick.

Now, there are cast in place ceramic or refractory liner systems listed to UL 1777 for a 2,100F rating at zero clearance to combustibles. Most use an inflatable rubber bladder form while Ahrens pulls a vibrating bell through a zero-slump mix that then gets a glaze coating. Again, these are high mass liners better suited for continual wood burning.

If you have the room, you could drop a metallic vent or class A chimney. These are, like the liners, low mass so they heat up quickly and maintain a stable draft. They are smooth on the inside so no derating and they flow great without corrugations to collect crude. Even on gas, use type L vent instead of B-vent. The ss liner does not rob heat as bad as the aluminum liner in B-vent so you get and keep a stronger draft with less condensation.

EK equipment is unusual compared to the rest of the market. You do what they say how they say or not at all. Most techs are not trained by EK at their facility to sell, install and service their equipment which is essential. If you don't have a solid EK dealer for support then steer clear. If he's the only EK guy in your service area, think about it if he disappoints you who would you turn to.

All that said, EK is great equipment with great performance. Just do what they say and not what the rest of the industry typically does and it will serve you well.

@charlie123 , FWIW, I have a customer with an EK and he loves it. And the EK folks were very helpful when I first encountered it. I can't over-emphasize following the instructions- a previous "tech" hadn't and the unit sooted up. But it's run fine since we took over.