I currently have a Lennox G12Q3(or O3)-82-4 natural gas furnace rated at 82,000 BTUH. It's about 20-years old. It works OK and my only complaint is the odd "hamper filter" it uses. The filter is a loose piece of filter material I wrap around a piece of what looks like garden fence. My daughter has allergies and It would be nice to be able to use a better filter. Can I retrofit this unit to take a new filter? Also, would it be cost effective for me to replace the whole thing with a more efficient new furnace since gas prices will be high this winter?