Furnace sizing opinions

moneymgmt

Right now I've got 800sf being heated by a 70,000btu 80% furnace. I live in Michigan and it gets cold here, having uninsulated walls doesn't help the problem. The last two winters my furnace kicks on and runs and runs and runs to the tune of a $200 gas bill in December, January, and February..... and I keep the temp at 64-67. This summer I'm finishing the bonus room upstairs which will make the entire house 1100sf. Now the fan motor is dead and I'm debating a couple things. Should I:

1. Replace the motor, keep the furnace
2. Replace the unit with a newer, same size, unit
3. Replace the whole unit with a bigger unit.
4. Replace the unit with comparable size but higher efficiency
5. Move to a warmer state (this is my wife's solution)
Thanks in advance for your feedback! Have a great weekend!

mrtech

How old is the furnace? If it's at that age to be replaced or is unsafe- replace it.
I would have a HVAC contractor do a heat load on the home to size the furnace and a/c properly, but not before looking into insulating the home and repairing any infiltration problems you may have in order to save on the cost of operating the system. These two are the most important for any home. Then the system can be designed for the more efficient conditions.

moneymgmt

Allegedly, the furnace is not that old, maybe 7 years. That's what the PO told me but I think it was a refurbished furnace or something along the lines of being re-newed.