Need advice on converting fuel oil to natural gas, what to do with buried tank.

My procrastination in dealing with my heating issues is not paying off! We bought a house built in 1898 without sufficient attention to the oil tank and boiler issues and now I could use some advice on the next steps to take.



We have a oil burning steam boiler with a buried tank (not sure of tank capacity or age.) It seems to work fine, just needs cleaning. However, the tank is completely empty. Since I don't know for sure whether it is sound, and oil is so high, I looked into converting to natural gas. We already have a gas line close by the boiler for our water heater.



I got an estimate for new firebox, Midco burner, smoke pipe, larger gas piping, city permit and chimney liner plus labor of $4230 (includes cleaning and servicing.) However, our chimney has a few twists and turns (3 story house and it also services a fireplace which we were instructed not to use because it's unlined and the chimney expert didn't think he could get a liner down it. He may just not have wanted to deal with it...)



IF we can get a 7 inch liner down the chimney to vent the gas burner, is this an expense worth paying in the long term? We plan to stay in the house at least 10 years. How important is it to have the oil tank evaluated? We have no indication it's leaking, but I am sure it needs to be dug up or filled if we are no longer using it.



If we CAN'T get the liner down, is it worth spending any money to do chimney work to make it possible? Would natural gas be enough cheaper than oil to justify a few thousand in chimney work over the long term? Is there any chance we could also get the fireplace operational if we do the chimney work? We would love to be able to use it.



Any advice you can offer would be greatly appreciated! The house is about 4000 sq. ft., seems to have a 2-pipe system on the first floor, 1-pipe on 2nd and 3rd floors.