We have a ranch with a wood fireplace in the living room. It's fantastic at heating the main living area, but the bedrooms down the hall get left in the cold.
I'm going to install insulated flexible ductwork in the attic, with a blower near the inlet (red), with outlets in each room. The initial duct will be 10", with 6" to each room.
This is roughly to scale, about 24' between the inlet and 2 aligned outlets. Fireplace is to the left:
I can either run 10" to a 3-way manifold, and take 6" runs from there. Or I can run 10" to an 8"/6" splitter, take one 6" off there, then run the 8" to a 2-way 6" splitter, and take the remaining 6" off there. The first is preferable, as I'll get more efficient use of the duct, which comes in 25' sections.
Will I see a noticeable difference in airflow one way or the other? If it matters, the lower-right bedroom is the master, and it's fine if airflow is a little less there (other 2 are kids' rooms, which we want a bit warmer).
Best Answer
In either case you have a 10" duct as the bottleneck in the trunk line. Expanding it downstream won't get you much in terms of flow. I'd go with Plan A.
Perhaps a more important question: Is the inlet attached to the fireplace somehow? You'll probably be disappointed if you just pull air from one room to another. The differential would be so small that you won't see much benefit. In fact, the air movement may make those rooms actually feel cooler.