Low heat output

[Montana_5429]

I just picked up my Mountaineer 342PHT today! When I run the furnace, I get tons of heat from the rear duct and the kitchen duct, but the 2 forward ducts, bath and bedroom, have real low air flow. I covered both rear ducts with heavy towels, and I only got a small increase of air flow in the forward ducts. Could I have disconected hose under the floor? Where would I access it? Thanks