Replies

1. 
   Piffin | Feb 14, 2006 05:52am | #1

   When the chimney was shared with a furnace, it stayed warmeer so much of the moisture by-product of the water heater combustion remaned in vapourous state and left the stack .

   Now you have very little heat going up the chimney so the mass of masonry stays cold. That means that most of the moisture in the exhaust is now condensing on the walls of the flue and driping/running back down and in. Lining it with a class b flue of the right size - probably 4" will help it exhaust to the exterior faster before it condenses.

   There is another feature you now employ in this setup which can be unhealthy. Since the flue is so large re the size required and the gasses cool down so fast, they sit there drigitn around, and there is an increased chance that they can leak back into th ehouse. That is not a good place to have carbon monoxide. I would suggest a tester

    

    

   Welcome to the
   Taunton University of Knowledge FHB Campus at Breaktime.
    where ...
   Excellence is its own reward!

1. 
   Rich | Feb 14, 2006 06:15am | #2

   Thanks, I do have a CO2 detector in the kids' bedrooms and in the furnace room where the WH and chimney are located.  Guess I'll have to look into getting the liner replaced.  Last time I did that on another house it was $500.  Might be money well spent to just change out the 4 year old WH for a direct vent.

2. 
   constantin | Feb 14, 2006 06:35am | #3

   A water heater by itself in a large chimney flue is a BAAAAD idea. Take it from me, the rear chimney in our home was waterlogged to 90+% due to being abandoned to nothing more than a gas water heater. The basement brick chimney foundation had holes large enough to stick a fist through and the stuff was spalling everywhere. That chimney came down rather easily.

   Between the oversized flue (reducing the air speed) and the large surface area, that masonary chimney of yours is never going to come to temperature unless you draw hot water 24/7 slowly but continuously. And if you're heating with natural gas, once the surface temperature drops below 140°F, it'll start condensing in there. And remember, the whole chimney has to make it to 140°F, not just the flue gases entering at the bottom. LP and oil have slightly lower condensing temperatures.

   As I see it, you have a couple options...

   • Line the chimney with a flue that is sized to the water heater
   • Go DV on the gas water heater as well.
   • Buy an indirect water heater and run it off your boiler
   • Buy a electric water heater (tankless or not)
   • etc.