We have a 1200 sq ft modular part time home located in northern Michigan. Average winter outside temps are in the teens and twenties, and it is often windy. The home was manufactured in 1978, with 3" thick exterior walls with fiberglass insulation. Attic insulation is minimal.

Heating is accomplished by a 70,000 BTU propane fired downdraft furnace with A/C. The furnace is about 6 years old, and the system does not have a return air duct system. The furnace is located in a central hallway; room doors are cut at the bottom so as to provide air flow under them if they are closed. Standard pleated filters are located in the furnace intake area in the manner the manufacturer (Coleman) designed, and are changed often.

My wife complains of dust throughout the home. Recently, she purchased and installed register filters similar to these: http://www.amazon.com/Vent-Filters-Pack-4x12-Register/dp/B002JKXW9A

I notice that airflow is significantly reduced, and I am concerned about overall furnace efficiency and longevity. I'm also concerned about the effects in the summer, as the 1-ton A/C system seemed to be barely sufficient without these filters.

What are the potential effects of these filters on the heating and cooling system, the overall cost to heat and cool, and the life of the system?