My daughter and son-in-law had a new furnace put in their house. They changed over from oil to gas, the installers ran the exhaust into the chimmney just like the oil unit was. Now they have water leaking out their cleanout door at the bottom of the chimmney in their basement. I know the furnace is only 80% efficient, and when the furnace is running if you have the cleanout door open at the base of the chimmney you can see water dripping down past the door in the inside if it. Do you make a drip pan of sorts and empty it every other day,or? Thanks
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This is really bad. They need to have a properly sized liner installed. They also need to have the draft checked. Preferably by someone who knows what they are doing.
Thanks for replying, your saying they need a liner inside the chimney?
here's the mechanics of what is causing the water...
All combustion appliances, make CO gas, water vapour, and sometimes other solid and gaseous pollutants.
In older appliances that were generally less efficient, a lot more heat was wasted up the flue with the exhaust gasses. You now have a more efficient unit so less heat goes up the chimney. It doses not burn as long and it does not waste asmuch heat when it is burning.
Unfortunately a by-product of that fact is that the water vapour is now cooler, and the column of air moving up and out is also cooler. Less heat is transfered to the sidewallls of the masonry chimney so it stays cool enough to cause the vapour to condense on the sides of the flue. That then drips back down.
Often it is not a problem. Lots of chimneys see more water from rain than from condesnate.
where it does become a problem is when there is no clay flue liner or when heating oil rather than gas is used and the sulphur content is high enough that the comnbination with the water forms sulfuric acid which weakens the liner and the mortar. This should not be the case with a gas appliance, as far as I know.
One error that is more common though is in the deign stage. It is common for heating engineers to oversize the heating plant, 'just to be sure...' That means that it will not run for as long a time on each fire up. If the unit runs longer, the flue can get heated up, less condensation will occour because it is being carried out with the rest of the gasses.
Someone who is good at it can adjust some of the limits on the burner so that it would run longer at each whack. That can be good and bad, and possibly even dangerous, but too short of a cycle time can be dangerous too. If it comeson and off too often, for too short a time, the flue will not get a draw going and CO gases can splill back into the living area.
The low limt setting tells the burner when things are getting too cold and triggers it to comeon. The upper limit switch tells it when it has enough heat available and it ios time to shut down. So by adjust low swtich lower and high switch higher, the burner will copme on less often and burn longer when it does come on
Don't try this yoruself tho. This is generic information only, to let you be able to discourse with the tech responsible..
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Correct on all points but one. The primary components of complete combustion are water and carbon dioxide. When the water vapor condenses it reacts with the CO2, and becomes acidic. Which is why condensing appliances require stainless or plastic venting. Even a clay tile or galvanized chimney can be ruined.
prv's controlling drips..............snicker
Edited 1/9/2006 11:00 pm ET by rich1
"prv's controlling drips..............snicker" means what?
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"prv's controlling drips..............snicker"
means what?
http://forums.taunton.com/tp-breaktime/messages?msg=68040.26
LOLThanks
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what effect would adding mica-fill to ss liner to fill up space between 8x8 so chimney would stay warmer .
Probably not code, and with properly sized liner, not needed.
So you are refering to the material the flue is made of re acids? It is also important for it to be sized right. If the existing lfue is a lot larger than the appliance requires, the column of air moving up and out with stagnate, moving slower and giving more time for the water to precipitate. A flue sized just small eough without being too small will eject the gases more quickly so they have less tiome to cool and condense.
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Yup. The type of material the vent is made of is critical for the application.
Replacement of furnaces usually results in oversized chimneys which helps to kill the draft.
While a high sulfer oil can be a problem, most condensate tends to be closer to carbonic acid.
Don't know about all the U.S. codes, but up here we have to line a masonary chimney or resize a metal one if it is oversized.
Your description is as good as any I've read.
Local codes will prevail on the the liner issue.
Local code here in Metro Louisville, KY. changed in Jan. 2005. All masonry chimneys that serve gas fired appliances are required to have SS liners installed when and if new appliances are installed. New construction requires a line flue, and has for many years now.
Good call on the formation of carbonic acid in condensate from ng exhaust. Like pouring a coke in the chimney ever day. If that stuff will eat a nail, it will slowly eat the mortar out of a masonry chimney.
Dave
"Don't know about all the U.S. codes, but up here we have to line a masonary chimney or resize a metal one if it is oversized."
In most of the US, the International Fuel Gas Code (which was previously contained within the International Mechanical Code) applies, as a minimum, and requires that the "chimney or vent shall be resized as necessary to control flue gas condensation in the interior of the chimney or vent and to provide the appliance or appliances served with the required draft".
In English that means, IF the existing material is suitable, chimneys do not have to be lined IF sized properly, for a good portion of the US. In reality, venting furnaces and small boilers through non-engineered vent systems, i.e. an existing masonry chimney, requires a liner.
The installer of the orignal poster's new appliance did a poor job, and as Bob mentioned, probably installed other portions of the system poorly as well.
>>Someone who is good at it can adjust some of the limits on the burner so that it would run longer at each whack. That can be good and bad, and possibly even dangerous, but too short of a cycle time can be dangerous too. If it comeson and off too often, for too short a time, the flue will not get a draw going and CO gases can splill back into the living area.I question whether anyone should fool with the limit switches; the high limit switch is to protect the heat exchanger from an over-fired burner; it is not intended to control the point at which the furnace burner shuts off except when the heat exchanger gets _too_ hot.The thermostat anticipator can be adjusted to some extent to lengthen the burn time.
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The draft issue has been well explored in this thread.
May I suggest having the whole installation checked by a competent HVAC tech; if the installer got the flue sizing wrong, who knows what else s/he screwed up?