[Mike in Arkansas]

A 100 year old house with updated HVAC currently but replacing with high efficiency zoned equipment. I have the upstairs done and am working on the downstairs now. Equipment will be installed in the basement. Its a 2 stage induced draft 50,000 BTU 80 plus non condensing furnace with an 18 SEER 2 ton AC. Optionally I may use a 90+ condensing furnace. Presently, the old induced draft heating unit (155,000 BTU) vents into an old 8 inch cement flue original to the house that runs from the basement to roof. Existing natural draft water heater also vents to this flue. The bottom of the flue is sealed. Is it safe to vent the new equipment into this flue? It is sound all the way to the roof so leaks should not be a problem. I suppose if I opt for the 90+ condensing unit it would no be acceptable because of the condensation but what about the non condensing unit?

 

[yuri]

Where I am they would force you to do an upgrade and install a liner inside the chimney AND size it smaller according to the combined BTUs of your furnace and water heater. Liner prevents damage to the innerds of the chimney (mortar) so it does not deteriorate and collapse. I would check with a local gas inspector or gas fitter about the code requirements in your area. Fail to do it to code and you could be liable if the next homeowner has problems and it may have furnace pressure tripping and condensation problems if it is unlined and oversized.

 

[Mike in Arkansas]

Thanks Yuri. Actually, the more I thought about it after posting the question, the more it didn't seem correct to me and doubt that its' really suitable for the present equipment.

 

[yuri]

Did you add a LOT of insulation/better windows etc? You need to do a heat loss calc to get the right sized furnace. Dropping 100,000 BTUs is a lot! I would go with a high efficiency furnace and electric water heater or direct vent one and abandon the chimney. Then you can remove it and gain some valuable closet space/real estate and make Momma even more happy. Good for use as a chase to run your wiring for your high end home theater system etc.:thumbsup:

Load Calculator

 

[Mike in Arkansas]

I did do a heat loss calc shortly after I bought the house. The 150k/5 ton ac heated and cooled the complete two story house and cycled even on the hottest days. The upstairs upgrade has been completed using the same equipment so I only dropped 50k heating and 1 ton AC. I prefer to keep the equipment running and really drying out the air plus we keep our thermostats set very conservatively. They are undersized for someone who wants to keep their house at 65 in the summer but that won't be my problem :no:as I'm not leaving until they carry me out. Can't replace my windows as I love the wavy glass, but better storms and insulation is in the near future. Not much efficiency gain on the 80+ furnaces but the new AC is 3 times more efficient.:thumbup: Also a 94% condensing gas fired instatanious water heater is in the future and it will be vented seperatly through a wall with PVC. Guess I'll just bite the bullet and run B1 vent out to the roof