Chimney Pipe installation

[DonRodarte]

I'm installing a Heatilator EL42. My first length using is 2' pipe then having to use a 90° elbow to get in line past the ridge in the roof. One elbow is not going to be enough. Can I used a second to get the clearance need? Will the straps on the elbow be enough to support? I asked the distributor if it was needed to apply a beed of heat resistant caulking and he said no? The double wall piping locks into place and will be fine? As my elbow goes towards the ceiling ( plywood since this is going into an existing screened patio) the pipe will be about 3-4" away from the insulated wall (no paper). Should I put a sheet of Hardy Backer on the wall for extra fire protection?
Sorry for so many questions. I just want to do it right and not burn my house down. This part scares me more after reading a lot

 

[begreen]

There are no 90º elbows in chimney pipe. The largest offset angle is 30º. From the installation manual:

WARNING! Risk of Fire! DO NOT use offset/returns greater than 30°. Chimney draft will be restricted and could cause overheating and fire. Secure offsets with screws ( not to exceed 1/2” / 13 mm in length) Secure returns with strapping. Straight chimney sections may be secured with screws. Keep chimney sections from separating or twisting.