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Discussion Starter #1
I installed a natural gas water heater the other day and immediately felt hot air coming from under the bonnet which would indicate a blocked flue. had customer set up for a chimney sweep to check out flue. Says it is not blocked but because the furnace does not use the flue any more it is over sized for the hot water heater, advise is to reline making it smaller. I'm not sure if I'm buying this, I would think if it was over sized it would take a little longer to heat up the air in the flue to get it moving. Would like any feed back on this. ( not stating weather pex or copper was used for this installation)
thanks Steve
 

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the chimnay should be relined.

it sounds like we have negative pressure in the house. i have seen where the furnace or ac fan will draw done the chimney. sometimes it's combustion air circulating around each other in a circle. usually goes up furnace flue to tee then back down and out the wh. not the problem here. i hope not. if we have furnace cold air return and wh near to each other, not separated by doors. so when fan runs we have a high & low sides. output side is high and return side is low. that's the inside of house, outside is between them. high pressure goes to low pressure, always. if high is +6psi and outside is 0psi, well we have air escaping. that's not important here. but if low side is -6psi, air comes in because of high to low. turn off ac and stop all air flow in house. that will answer that. ac fans are normally higher speed than heating speed.............chimney will no draw correctly the air just circulates in it. look in your gas code book there are tables of diameters and lengths for vents. if it's not lined we have a carbon monoxide problem and a acid rotting chimney. liner will work better if it insulated if it gets cold out in winter. breid
 

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Discussion Starter #6
Ok guys its running into the same chimney it always has so I guess they do need a liner. thanks again for the help.
 

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Thing that baffles me about this is the water heater vented into this chimney along with the furnace. But the furnace only runs , lets say 6 months out of the year. So does this mean they had this issue the 6 months the furnace did not run? I mean with out the furnace running in the summer months wouldn't the chimney be considered over sized during that time as well?
 

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Do you know for a fact that the old water heater didn't have exhaust gases backing out the hood? Maybe your just the first person to pay close enough attention and notice it. Here we have to have the chimney lined no choice. also is there any other things going on that the customer may have not told you? attic fan on or something you missed?
 

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chimney

there is a good chance, real good that it did this 365 days a year. when furnace wasn't cooking even in winter. i have seen houses with large chimneys that showed no vapor in the winter. i run every morning and it became a game to watch. i presumed that the chimney was circulating inside itself. some also leaked so bad that they didn't show a draw. ..............when i said insulated, i meant double wall..................all chimneys around here were built for solid fuel (wood or coal). breid
 
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