Construction of chimney sandwich tubes for gas boilers.
Sandwich tubes have proven themselves in the market of services. This is understandable, because they have a number of advantages, the main of which is a long service life( of course, if you acquire a quality product) and a high degree of fire safety. The material consists of stainless steel, which means that they are not threatened by the aggressive environment in the form of high temperature and outside air. Plus, everything does not settle with condensation or soot. 
ST are easy to install. Installation is possible both inside the house and outside. You will be able to save a little money, due to lack of need to build a foundation. All elements and parts are very easy to assemble, so a chimney can be made even by a person who does not have any skills in this area.
Naturally, there are several drawbacks. Despite the long service life, they are not as "durable" as chimneys built of bricks. They are characterized by high cost, and also, the probability of leakage of joints is high. This is due to the fact that in the pipe there are constant temperature changes.
As we said above, the CT consists of high-alloyed stainless steel. But that is not all. Sure, you noticed the familiar name "sandwich"( with a sandwich) and it's no accident. Builders know the term "sandwich panel" - this is a kind of three-layer construction, which consists of two sheets of solid material and a heater in the middle. CT is also inherent in this design, but it looks a little different: instead of rigid material, we have 2 pipes with different diameters, and the empty space that remains between them is filled with a special heater. It is resistant to high temperatures and, as a rule, consists either of fiberglass, or of special mineral wool, based on balm. 
Installation of the CT is carried out in a new way: the length of the sections is only one meter and they are easily connected to each other. The diameter can also be different: wide or narrow, depending on operational requirements.
Installation of chimney sandwich tubes.
Before installation, you need to make several purchases, which include: deflector, spark arrester, brackets, crimp clips, apron, revisions, knee( if necessary).
When installing this construction, it must be connected to the boiler, fireplace or stove using a fitting. Further all is simple and elementary: we insert one element in another, thus we fix all the above mentioned brackets.
Remember the basic rules. First, if the roof is flat, then the pipe should be installed no lower than fifty centimeters above the plane. A slightly different case with a pitched roof. CT should be no lower than fifty centimeters above the level of the ridge, if it is closer to it than half a meter.
Secondly, if the device passes through the roof, it is necessary to use a steel sheet( put on a pipe), in which the diameter of the hole will be equal to the diameter of the pipe.
Third, the design should be wrapped with a silicone sealant. It will not allow moisture to get into the under-roof space.
Well, in the end, on the roof do not forget to install a metal sheet, and then get it under the skate. This sheet is fastened with roofing screws, with a silicone or rubber gasket. Do not forget to coat joints with silicone sealant. 
Successful installation and let the chimney sandwich tubes for gas boilers will last for many years.
