We have a 1922 house with a chimney that goes through the center (no fireplace). I had the furnace inspected (furnace and water heater new in 2001) and it turned out fine. But, the guy said that our water heater tube and furnace tube need to connect and feed into a big hole in the chimney - then into a chimney liner which we would have to install.

Right now, both the water heater and furnace run separately into the chimney and there is no liner.

I asked the city inspector and he didn't think this sounded right. It's $400 and a permit, so if it's not needed, I would rather not get it. On the other hand, I don't want our chimney to get ruined due to condensation.

Any advice would be very much appreciated!

How old is you furnace? This would be the only reason to have a liner. If it is a newer furnace the flue gases will condencate and cause moisture in your chimney

It's from 2001

Then I would say yes, I would recommend you get a liner.

They make flexable liners that you can install yourself. Without too much problem.

It really depends on the efficiency of the furnace. It may be just as easy to put two lines. They are nothing more than flex tubes. Then put a chimney cap on the chimney.

With any old chimney, your safe bet is a chimney liner. But, if you have an 80 percenter furnace, you should be fine without a liner. If you had a ninety+ furnace, it shouldn't be going out through the chimney in the first place, it should be going out a side wall. Or out through the roof separately. If your city inspector says its OK, let it be. If you are truly worried about it, I would have some other techs in to give you the low down. Most pros should be able to tell you if it is necessary or not by looking firsthand at your situation. Hard to say from here. Good luck and please let us know what you decide.

You absolutely should not be trying to use a ceramic or brick chimmy, the reason is that in order to vent properly the gases must stay hot in order to rise out of the chimmy since these gases are heavier then air and will fall if allowed to cool. The best way to solve your problem is to run the same size vent that is on the water heater and same on the furnace(two vents) in double wall "B" vent or step up one size of the largest vent and tee into vent at the bottom of chimmy yet higher then the vent on water heater and furnace. This only applies to non condensing furnaces, which needs to be vented alone using PVC pipe. Good luck, Mike.
P.S. a bad vent can kill you , take care.

I would not run 2 seprate lins as sugested above 1 flue liner will be plenty, why spend the money for 2. As long as your furnace is under 125,000 btu's you can put it and your water tank into the same 6 in flew liner. Also they make power vents for around $375 that you can vent both units right out threw the wall.