I am in the process of installing a Modine HD75 Hot Dawg heater in my
attached garage and I have a question about the power exhaust and the
proper vent pipe to use. I'm looking at the installation instructions
for the unit and I am trying to figure out if I can use 5" Metalbestos
type B double wall vent pipe with the heater. If the unit has a
built-in power exhaust does this mean that I need to make the vent
pipe air tight (positive vent pressure, category III)? The
instructions state that that all vertically vented heaters are
category I venting (negative vent pressure). I plan on venting the
unit vertically through the roof of the garage. If the vent pipe has
to be air tight is it possible to use the metalbestos double wall pipe
and somehow seal the joints?

x071907 wrote:

I am in the process of installing a Modine HD75 Hot Dawg heater in my
attached garage and I have a question about the power exhaust and the
proper vent pipe to use. I'm looking at the installation instructions
for the unit and I am trying to figure out if I can use 5" Metalbestos
type B double wall vent pipe with the heater. If the unit has a
built-in power exhaust does this mean that I need to make the vent
pipe air tight (positive vent pressure, category III)? The
instructions state that that all vertically vented heaters are
category I venting (negative vent pressure). I plan on venting the
unit vertically through the roof of the garage. If the vent pipe has
to be air tight is it possible to use the metalbestos double wall pipe
and somehow seal the joints?

You must tape the joints with metal tape. I have a Hamilton Home unit and
they say
to seal the double wall joint in the pipe.