From someone who has tried...
The problem I had was... they type I have has a combustion area, and the
air actually is just blown over the outside of it. (air blows out only
though the outside area of the internal combustion tube)
The result was, when I added ducting, the increase of back pressure
would cause some air to be blown backwards into the combustion tube and
puts out the flame. Not all are built this way, but many are now.


Mike

dave wrote:
Another thread made me think about using the portable propane heater I
use in my garage to preheat my airplane. It's the standard metal tube
type with the fan from Home Depot or Lowes. I've seen people simply
attach a flex duct to the end of this type heater and blow the hot air
into the cabin - poor man's red dragon. Any drawbacks?
Thanks
Dave