Gas and Oil Home Heating Furnaces - rheem furnace questions

have a furnace removed from another house: Rheem Criterion model RGDG-07EAUER .It doesnt show on their website so I assume it's no longer made.It's nat'l gas and has a Carrier central air unit/condensor that came with it and was a good working unit as well. The outside dia on the ex stack is just under 3" and seems to be made for the PVC to slide on and go from there with the connecters etc to get my vent out.Is there supposed to be a type of rubber(?) flange connector at this to go from the stack to the PVC? I can tell there was some silicone sealer at one time there as I peeled some off.You can also tell this is the first time I've done anything with this type of vent.I installed the previous hand-me-down gas furnace I recently removed but I've only had experience with metal flu type furnace , and rely on "those who know" when it comes to the elect. part of installation.I have the plenum completed and want to make sure I do the vent correct. I have planned on running the vent through my basement area up at what Ive been told at 1/4" for every ft. and it will pass through the side of foundation above the brick through the outer floorjoist/plate. It will be aproximate total length of 12'.Thanks in advance for any advice.

For one I cannot believe you would be using a used furnace in your own home and this must be a rental. Please for the sake of the people living in this home get a pro to look at it and make sure it's safe.

We do not mind helping a diy'er at making repairs but installing a used furnace and not even knowing what type of flue it requires worries me.

I appreciate your concern and agree.I do have a professional that is going to look over everything I have and is doing final installation. I did however install the prior furnace that was gas furnace .I had a pro wire it and a pro go over everything I did.It worked without a hitch .The reason I am installing a used furnace is that the furnace had only been in use for 3 yrs and was given to me.The house it was in prior to now was set for demolition because of a comercial exspansion project.The furnace in perfect working order wouldve been also destroyed. I stored it for the untill now. It is definately an update from what I now have.I am trying to accumilate all the mtrls. needed before hand.The pro that will be making sure everything is correct is out of town at this time. I wouldnt dare install a furnace without knowing it's done correctly.Before I even considered this project I had the pro inspect the complete unit. If I could ask him this vent question I would. I thought before hand I could inquire and possibly learn a bit more. Before I considered asking I browsed through this forum and saw several similar,although not exact questions. I also saw that I wouldnt be the only person without complete knowledge as to this subject asking questions.I realize your concern and appreciate it. It seems I will have to wait and see what he says when he returns.Thanks anyway.

now have the furnace I asked about operating and the vent hooked up correctly ,even programed and installed the thermostat/all wiring worked right off the bat.It turned out that this Rheem reguired a direct 3" to 2" as it left the furnace and I have it at the proper rise and all hooked up.Ran it though th cycle several times already .Next step is hooking the Carrier ac unit...have the pad set and cleaned the condenser and parts related.Bought the line set...I cant believe how much more most places want for line sets on line compared to a local supply close by me here in central IL....about half the price.It pays to check localy before you jump on something at a lot of web sites sometimes.

that is a common unit, you should have found info on it

what is the serial#? that will tell us more