The old furnace vent was removed from the chimney and now sidewall vented?

The furnace salesman should have advised you on proper water heater vent sizing since they removed the heating appliance from it and informed you that a smaller proper sized chimney or liner would be required.

Did a professional company do the work, then ask why you weren't told.

In either case, you have a potentially bad condition with probable venting problems, future complications and possible health/life concerns.

The furnace is now sidewall vented and they never changed the original vent. It The 2 of them use to flow out together and all they did was cap off the line going to the furnace. It was a professional company here in Chicago. I'm thinking I might have condensation on the inside of the piping and that is what is dripping??

Yup

Because flue is most likley too big now

I'm not sure what code is here, what I know for sure is 80% efficient furnaces end up with a lot of condensation in the vent as well as corrosion from condensation. They are terrible and I would always recommend the sidewall vented 90% units.

In addition, I can't imagine that it's code to put a forced vent appliance on the same flue as an atmospheric vented appliance.

All that said, you need to check the venting for proper size and also for corrosion. An insulated vent may be in order. Someone who knows venting code better than I can help you out.

Jake, what?

80% units don't condense, improper chimneys however promote the condensation of it's gases.

Fan + Nat vents work well together if done right, besides being listed in every vent sizing table available, recognized by AGA, NFG, NFPA, .........

What is the size of the vent? IF your hot water tank is the only appliance venting in that run, the vent is likely too large and by code should have been re-sized by the furnace installer. You don't tell us your HWT btu or chimney height, but most times it requires a 4" vent by itself. The vent is likely too large and therefore the flue gasses are condesing as they cool down too fast. A properly sized vent will have no condensing in it even with a mid effient furnace.

I'm admittedly not a venting expert... What I've seen in experience is that just about every 80% furnace has a rotting vent due to gases that are already near the condensing point condensing in the flue (including my own, several years ago). Perhaps all the ones that I've seen have been poorly designed-- I don't know. It has been enough to convince me that I would never bother with an 80% furnace.

I believe you when you say mixing fan+nat is permitted... I just can't imagine the reasoning. I never understood the reasoning that would allow combining a furnace and a water heater in one larger flue either. For a good portion of the year the water heater is going to be the only appliance using the vent... wouldn't the vent be oversized for the 3/4 of the year that the furnace isn't running?

The issue does not usually occur in combined vents since the heat is off when the temp is warm, resulting in lower cooling loss from the WH gases.

The vent should be reduced down to the size required by the water heater alone if the furnace is no longer sharing the vent.
While it is unlikely to get bad enough to choke off flow, it is NOT a safe installation.

I think my vent is 4", I have a Bryant Plus-80 furnace, and I just replaced my hw heater, (I'm in BC Canada so YMMV) - the flue hat for the hw heater is sized for the vent that's there, I hadn't thought of that aspect - if I replace my furnace with a HE one - since I just shelled out on the new hw I wouldn't want to change it just yet (but I guess I would run the plumbing for a he hw heater when I do the furnace-

Both furnace and hw heater Y into a single vent of course, if it was hw only, would there be a reducer that runs off the flue hat? I could certainly see a difference if it was only one appliance using the vent, but I've never seen any condensation coming back down....I wonder if OP's issue might also be some negative pressure....which could be dangerous.

jmnoelle13, can you try a test for us? Get a stubby candle like a tealight, and place it right next to the flue hat on top of your hw heater, when the heater's at work, and see if the flame of the candle is drawn towards the flue hat? If it is, all is well in terms of airflow, if not, your system or parts of the ventilation system in your house is drawing combustion products back down the vent, which is very dangerous. Your new furnace should have two side vents, one for exhaust, one for combustion air. You probably didn't have direct combustion air feed before, so you should be better off in that regard.

As for reducing the vent size, can you drop a sleeve down inside the vent from above?

Could a power vent be retrofitted, and can they use the existing b-vent, or are they they things that use pvc and side-venting too? Would the increased velocity help?

What about an increased hw temperature?

PJB999,

I am almost sure the brown water is condensation, although it could be rain/snow water if there's no rain cap.

The OP needs to check the vent size and replace if the vent is too large. The person who did the work should have advised him on the issue if, in fact, the vent is now too large.

If you live in Canada, really consider a 90% furnace and possibly a tankless gas heater. Since both are sidewall vented, you can solve some venting problems. In my area, it's was/is a common practice to vent water heaters into a masonry chimney.

I moved to a tankless in part to solve that problem.