Best heating ducting avail

Ok lets see if the forum wiz's can come up with some answers to these questions :)
Where can you buy insulated, rigid heating ducting?
Where can you buy duct with an R value greater than 1.6?
Why is flexible ducting used almost exclusively on domestic install?
I have read that the maximum recommended length of flexible ducting is 6 metres ( http://www.westaflex.com.au/_pdfs/du...troduction.pdf ). Is this so?
We will be putting in a new zoned gas heating system with our renovation and the main line of the ducting will be in the unconditioned space under the floor. I wish to achieve the best efficiency possible. As an example of what Im trying to overcome, I measured the external surface temperature of the main heating duct that we have under the floor with an infared Fluke thermometer, with the heating on, last night. The air temp was 13 deg and the measured external temp on a sound piece of duct was 31. Seems like a huge waste to me.


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