Yes but consider that you live in an area that gets fairly cold in winter and your furnace must be far past its expected lifespan by now. Unless you have alternate means of sufficiently heating the home, it is due for replacement. You can take your time getting bids on replacement cost if you're not in a hurry from it being 0F in winter at the time of failure.
I have looked into it but the thing is ancient and seems to be working great.
approx 1700 sq ft house kept at 70 most expensive gas bill this winter was $170.
what type of failure would you suddenly expect at 0F?
I did change the blower motor and capacitor last fall due to a squeak that would only go away temporarily with oiling.
what would be your price estimate installed, mb a 100k BTU 95-98+ not sure if modular is good or not? more things to break
Ancient and working great means you aren't at a hardship to shop around for the best replacement cost, as I mentioned.
You do not need 1000K BTU for a 1700 sq ft home. Not even close unless it is very poorly insulated or sealed.. A properly sized unit will cycle on and off less and wear out slower as well as reducing the operating cost. Do NOT believe some of the BTU calculators out there unless your home is incredibly lossy and if it is, invest in better sealing and insulation first.
Price estimation depends a lot on what your exact specific setup is. Measure your furnace width. If it's 17.5" an 80K BTU is your best option. If it's 21", go with the 100K BTU. This will make it as near a drop in replacement as possible and save the labor cost of extra adaptation. Granted I am making several assumptions without seeing your setup and could be wrong, am just doing some kind of mental averaging of cost and situation.
Why are you focusing on 95-98%? That's like upgrading from a yugo to a Cadillac. There is a sane middle ground, don't be duped by HVAC affiliated companies who are just interested in ideals instead of your cost.
Either you do or you don't already have intake inducer air piping with an induction blower setup. If it is an open ventilated area you can get an 80% efficient furnace the cheapest but otherwise shoot for 92% efficient to use or add existing ductwork for inducer blower airflow. That ductwork (I should call it piping since most often it is just standard PVC) will require labor and a smaller material cost.
The type of failure I"d expect at 0F is the worst kind, that if it is very cold when it fails, it is inhospitable in the home so you are in a rush to repair it without having the time to wait on competitive offers.
The older what you have is, the more it may deviate from modern furnances so an estimation is impossible without very detailed site survey info, but suppose it was just a drop in installation of same size furnace and the A/C was not replaced, recoverable due to more recent replacement or whatever, or you opt not to do A/C, then the 100K unit can be had for around $1000 and the installation can be had for around $1200 but again this depends greatly on what is there and what has changed since your ancient furnace was put in.
The main thing is, do not wait until it is urgent to repair it quickly. Get competitive estimates NOW, and then if you want to wait and see if they will honor those estimates when the dead of winter is upon you, at least you have more info then.