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Old 02-24-2011, 08:20 PM   #1
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gas hot water tank venting in chimney w no furnace...


About 4 years ago I had a high efficiency furnace installed. The exhaust for the old furnace vented into the chimney along with the hot water tank. The chimney is not on an outside wall, and is central. The installer didn't think it was a big deal to leave the water tank vented into chimney because it was central (there is no separate liner for the water tank exhaust in chimney). The new furnace vents directly thru the glass block windows in the basement. I have numerous carbon monoxide detectors in basement & first, second floors and they have never gone off. I know this set up wouldn't pass inspection, but wanted to find out if I should bother changing it and if I did, what are my options. I have a slate roof and my chimney is covered with a cage to keep critters out, so it would be a pain to add a liner into the chimney.

I heard that small amounts of carbon monoxide can seep thru the brick & mortar into the house if its not escaping thru the top of the chimney. My house is a cape code style built in 1939 and has a low attic.

Thanks in advance for any feed back


Last edited by dbldee20; 02-24-2011 at 09:20 PM.
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Old 02-24-2011, 09:41 PM   #2
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gas hot water tank venting in chimney w no furnace...


The safest method if your worried is get an electric tank, then it can sit anywhere.

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Old 02-24-2011, 11:27 PM   #3
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gas hot water tank venting in chimney w no furnace...


If your chimney is too small for just the water heater to vent into, then the water heater's exhaust will condense before reaching the top of the chimney and rot out the clay liner. Considering that your chimney was supposedly big enough for the water heater AND furnace, now that the furnace exhaust has been routed elsewhere, it's almost guaranteed that you need to install a chimney liner.
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Old 02-25-2011, 01:51 AM   #4
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gas hot water tank venting in chimney w no furnace...


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Originally Posted by hvac benny View Post
If your chimney is too small for just the water heater to vent into, then the water heater's exhaust will condense before reaching the top of the chimney and rot out the clay liner. Considering that your chimney was supposedly big enough for the water heater AND furnace, now that the furnace exhaust has been routed elsewhere, it's almost guaranteed that you need to install a chimney liner.

OR... you could cheat a little and open your clean out and let a little warm air from the base help keep the chimney warm on of cycle. The idea is that most homes withs chimneys in the center of the house don't need lining because it is surrounded by the four warm room walls.

Just an Idea...
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Old 02-25-2011, 04:27 AM   #5
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gas hot water tank venting in chimney w no furnace...


Removing the cage/screen to drop a liner may be a PITA, but not as much as having to have your chimney rebuilt because you didn't drop a liner in.

If your water heaters breech/dilution hoods opening is 3", then the inside dimension/area can't exceed 49 sq in by code. This doesn't take into account the height of the chimney, so for many water heaters, even 49 sq in of cross section is too big.
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Old 02-25-2011, 08:21 AM   #6
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gas hot water tank venting in chimney w no furnace...


Thanks for the ideas and info. I have 2 fire places. One on first floor and one in basement game room. So the chimney is fairly large.

Does anyone have a cost estimate to have a liner installed. The roof is slate so I am concerned that a contractor doesn't crack any of the slates. The roof in back of the house is a giant dormer so its not as steeply sloped as the front. Before I bought the house someone repaired the flashing around the chimney and broke about 10 slates by walking across the roof, which I had to replace because my home inspector didn't bother to look at the back roof. I've used 1/4" plywood myself to lay on when repairing some of the slates which works and wont crack them because my weight is dispersed over the plywood. So it could be something I would consider tackling myself.

The current water heater is somewhat small and runs out of hot water after one full load of laundry on the hot setting, so changing the water tank isn't out of the question.


Last edited by dbldee20; 02-25-2011 at 04:16 PM.
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