I went ahead and decommissioned the oil tank which cost me about $900 bucks. No leakage. They cut a 3x3 ft hole in the top, cleaned it out and filled with slurry mixture. Got my certification from the state.
Next I found a licensed HVAC guy through a house flipper, who came highly recommended. He gave me a great deal on a single speed, 95% efficiency gas furnace. We agreed on retro fitting the new furnace to my existing ductwork, as well as running new heating ducts to a back portion of the house. Total cost for furnace, install and haul away: $4600.
I put the house on the market June 7th of this year. I had 4 offers in 3 days. House sold for $13K over asking. Basement needed a radon gas mitigation unit installed ($1500) and some other minor fixes. Whole process went smoothly. Couldn't have asked for a better outcome!
I'm now in a nice, new-er home 10 minutes from work and couldn't be happier!
If the tank is old and has leaked into the soil then it makes it even more complicated.
If the furnace is damaged and a health hazard I would replace it; otherwise I would not even bring up the subject. Let the buyers chose. Oil could be benefit for some. You would sill have to decide on a gas or oil furnace.
If you do not switch to gas then it's up to the buyer to pay for a tank inspection to see if there is anything leaking. The buyer does not have to get an inspection but any good broker would "highly recommend" they get one. If it is leaking then a report will be filed with the DEQ. Someone is then obliged to remedy that situation, most likely you, which could cost as little as $1000 or as much as $6000 (or more). If you decide to switch you still have to abate or remove the tank, again $1000 plus dollars on top of the new furnace.
Gas is cheaper now but a good oil furnace can be a real workhouse and last for decades with proper maintenance. It can also burn biodiesel. Which may give the owner some flexibility as alternative fuels become more prevalent or you decide to make you own fuel.
Please call me with any questions, 503-866-6670.
In order to be proactive, I would probably get estimates to show the buyer what it would cost and help to educate them as to whether they want you to convert it, or leave it for them to do with a potential credit from you.
You can educate your self as well and use as a negotiation tool.
Hope this helps,