Water Heaters - what kind of water heater?

I rent a power vented water heater that is vented through the roof because there is no acceptable place to vent it through the wall. The exhaust would be bothersome to either my neighbours or myself. The problem is condensed exhaust water runs back onto the fan unit and rusts it out is a few years. I wish to buy my own water heater but I don't like the power vented model because water running onto the motor and also it seems noisy.
I have a chimney with two flues. One has a wood stove connected to it and the other has a gas fireplace. Is there any way that a standard water heater and another appliance can share a flue? I believe the flues are fire clay 8" by 14" .
Is it possible to create a water trap in the power vented exhaust pipe? By water trap I mean a lower point in the 2" ABS pipe with a small diameter drain line coming from it draining into the reagualr plumbing?

In theory multiple appliances can share a flue provided it is correctly sized. Most water heaters use metal flues like B-vent so I would check with the manufacturer to see if they can see any problems with using a fire clay flue. You would need to get someone knowledgeable about gas appliances to check what the correct size of the fule would have to be based on the BTU ratings and the venting tables. These can usually be found in the gas code book.

As for the other question - I guess a more appropriate term would be a condensate line. Many high efficiency appliances do in fact have such lines to drain the condesation so you could probably make something that behaves in a similar manner.

I have learned more on this forum in one night then I could have imagined.
I'm going to remodel my basement and now at least I know what I'm up against in regards to moving my water heater.

Good luck wih the project