Gap between hot water heater exhaust and chimney

Old 02-13-11, 02:52 PM
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Gap between hot water heater exhaust and chimney

There is a gap where my hot water heater and oil furnace exhaust meets the old chimney in my house. It looks as if the old mortar used to make the seal has fallen off.

1. How concerned should I be about this? No CO detectors have gone off and I am sure it has been like this since I bought the house 3 years ago.

2. What do I use to once again fill this gap? I am sure there is some kind of special high-heat gum-like substance used now a days. Can I use whatever it is with the furnace running? Its cold in the northeast and shutting down the heat for more than a few hours is not an option.

Thanks in advance.
Old 02-13-11, 05:19 PM
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You can use ordinary mortar, furnace cement (should be available at any plumbing supply house), or Hi-Temp silicone. The mortar or furnace cement would be my first choice because of set up time. The silicone needs to cure several hours before heat is applied.

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