I have a manufactured home - downdraft furnace and in-floor ducting. I bought a new Nordyne/Intertherm furnace 2 years ago. It is ready for A/C up to 3 ton and has a 3 speed fan.
The addition on my place was not heated (including the bathroom in the addition) at all! Last summer I ran a 6" pipe and took 3 - 4" takeoffs for 4"x10" registers. The 6" line runs perhaps 15', the takeoffs vary in length, one is ~2', one is ~3' and the last one is ~7'. All of these lines are insulated with reflectex. This addition is not very big, it's 14' x 12', and it is split 3 ways:
10' x 12' den (put two 4" x 10" registers here)
6' x 4' walk in closet (one 4" x 10" register)
6' x 4' entry way (there is a register from the main unit located in the opening to the main house so didn't bother with one there.)
This winter has been so much better since I insulated everything properly in this addition (I haven't got a clue what the previous homeowner was thinking, only half the walls and roof were insulated... )
The heat/dampness is much better in this room now but there's not much airflow, and when it got to -15 C here the addition was a few degrees cooler, and I suspect that's mostly because of the lack of airflow.
I saw someone servicing the HVAC at work, so I asked for his opinion. He suggested that the fan should be bumped to medium speed if it isn't already and some vents should be closed in the main unit to try to balance the air flow out a little. He showed me a CFM meter (?) that he normally uses to do this. This does make sense to me, but I found out he only works on commercial equipment and doesn't do residential. Doh! It sounds like he knows what he's doing...
I don't have the tools to do this kind of work, so before I call around, does this plan seem like a logical thing to do? Last thing I want are companies telling me I have to have all of the ducting redone when it doesn't need to be.
Thanks for any input,