Brown liquid from flue pipe

[essenz]

I have a house with an asbestos flue. The water heater and gas furnace have regular sheet metal flue duct, then up in the ceiling the metal flue slips into this ceramic/asbestos flue - 6" diameter.

There was no heat for about 1 year, just this past week got everything back together.

One problem, there appears to be a brown liquid dripping out of the asbestos part of the flue, it then trickles down the metal pipe. Not alot, just a small drip from time to time - but messy and concerning nonetheless.

Any idea what this is? Should I be concerned?

Thanks John

[jamesgangnc]

Yes, you should be concerned. The brown liquid is most likely water with various contaminants mixed in. In your case it is probably caused by the flue not staying hot enough all the way out. When you burn gas one of the resulting products is water vapor. The way 80% and lower effeciency heaters deal with that is to keep the flue temp high enough so the water vapor does not condense out. In the original installation there was probably enough heat going out the flue to do that because the original furnance was not very efficient. As furnaces have gotten more efficient there is less heat in the exhaust. It may be possible to install a liner in your old flue to prevent this. Or you may need to have a newer flue installed. You do not want to just ignore this because the other combustion byproducts make that water corrosive and it will damage the flue and the furnace.

[Tekkie®]

essenz posted for all of us...

It's essence

[essenz]

Well, the liquid is definitely condensation.

The flue from attic up to roof is 6" diameter asbestos/concrete product - difficult to remove.

So I want to explore my other options. I tried lowering the fan speed on my furnace - thought was slower speed = hotter exhaust through flue. No luck.

The other problem I have, which may also be a cause is my thermostat. Its a new digital programable Honeywell, and it attempts to keep the house at exactly the set temp, without deviating a single degree. As a result the furnace short cycles. Heat goes on for maybe 5 minutes, then off.

There are no settings on the thermostate to help out, so how to remedy this?

Ideally, if I set the temp to 68, I want the furnace to kick in at 66, then shutoff at 69. Having that 3 degree gap, will allow the unit to run long enough so there is no condensation. But how do you force a thermostat to do that?

-John

[Noon-Air]

You *DON"T*

You pay to get it done right the first time

[jamesgangnc]

There may be an adjustment in the thermostat. Check the paper work that came with it. Otherwise try the original one and see if that helps.

You still may have flue problems. They make liners than go inside older concrete/chimney flues. They are flexible. Your local hvac folks will have plenty of experience putting liners in and it should not be too expensive. Your current flue may be too big even for the combination of the water heater and newer furnace. Condensation is acidic and will deteriorate the concrete and cause it to develop leaks. That can result in carbon monoxide problems or cause a fire. I'd get it fixed right rather than attempt to work around the problem by playing with the furnace run time.

[HVAC Guy]

Maybe wrap it in insulation inside (the section of it inside the attic).

That means more heat up the flue, which means a less efficient furnace which means larger heating bills. No, you don't want that.

There might be a setting on the back of the stat, like a jumper or small switch. It might be referred to in the instructions as setback, span or hysteresis. It might be settable through the menu system on it's front panel. If you can, set it to 2 or 3. It is probably set to 1 right now.

Also, put a cover or shield over the stat (like the clear plastic box you see in commercial situations like offices). This might help keep it running longer in between calls for heat.

[Bubba]

??? Are you for real? Wrap a oil furnace flue pipe with insulation up in the attic where you dont usually see it? You are scary man, real scary. Have you ever wondered why you need an inch or two of clearance completly around the flue? Here's a hint. Its NOT to keep the flue pipe from making babies.

Holey chit! You got something right!

More genius material at work.

Dumb, dumber and dumbest. Longer run cycles mean longer off cycles. Hmmm, that ought to be a really comfortable house.

Give it up "havclueless". You havent a chance Bubba

[HVAC Guy]

If his flu pipe is condensing then it's too cold to cause conventional fiberglass insulation to "combust". Conventional fiberglass insulation can be used up to 250 f (according to Owens Corning) and probably higher (fiberglass insulation is non-flammable last time I checked). There is pipe insulation that is rated for up to 800 f.

Because wood burns, and most framing, flooring and ceiling joists are made of wood.

An attic flu that is not insulated is radiating heat inside the attic and that is bad news in the winter for all sorts of reasons. Insulating it will raise the inner flu temperatures and hopefully prevent water from condensing inside it.

Did it ever occur to you that setting the span from 1 degree to 2, or from 1 to 3, does the same thing (longer on time and longer off time) ???

That is exactly what the OP is looking for.

He could also turn down his burners so that the furnace runs longer (but cooler) so that the heat output of the furnace matches the heat loss of the house.

[Bubba]

Your right. I give. Id rather burn my house down or turn my burners down causing soot, carbon monoxide and water. Sounds great to me. Bubba

[HVAC Guy]

Like I said, fiberglass insulation doesn't burn, especially not at 300

- 400F.

Oh I see, your furnace currently doesn't generate any of those things. A furnace that doesn't even generate carbon monoxide eh?

[Dave]

Careful, You might get calluses in mouth from all that tongue in cheek!

[Bill]

I bet there's a law about retards pretending they are in another's trade.

You need to keep your uninformed mouth shut before someone gets hurt listening to your crap.

[Bubba]

.....and like I said......If you wrap fiberglass insulation around a oil burning flue pipe in an attic you are a clueless retard that needs to borrow Stormy's rock.

Currently, my 90+% gas furnace puts out less than 10 PPM at the flue outlet (thats, outside incase you didnt figure that out). This is well within the norm.

You really should get a clue on what you are doing and the physics of air and fuel combusting. Bubba