TT Prestige 110 exhaust

2" venting

3" is better if you have the space.  From http://www.triangletube.com/documents/1/Prestige%20Vent%20Suppl_PVC_CPVC_PP%20_SS_0412.pdf



2 Inch Vent Systems Restrictions for the PRESTIGE 60, 110 & Excellence.

-    Derate the maximum boiler input by 3% when using the maximum equivalent length of 2 inch vent piping on Solo 110 & Excellence 110.

-    The 2 inch vent system requires a 1 inch clearance to combustibles

-    Use long sweep elbow to limit pressure drop and to avoid excessive vent temperatures.

-    In 2 inch PVC vent applications, the first 7 equivalent feet of the vent system must utilize CPVC material.