No you won't damage your furnace. Your far more likely to cause damage with dampers. You need a minimum airflow in the furnace NOT to damage it. Booster fans just overcome some of the air resistance introduced by long ductwork. You would add these to the vents furthest from the furnace.IVB said:The problem is that I live in Northern California, labor rates *start* at $90/hour and rapidly rise. A simple slam-in-install is cheap, but the measuring & balancing is big $$. Tough to justify it, but easy to justify DIY experiments. I hadn't thought about using a blower to increase, wouldn't that potentially damage the furnace? I admit to not understanding the mechanics of furnaces and whether i'd create a vacuum situation burning out the furnace blower.