Condensation in oil flue pipe.

[jrc2905]

I went to service a oil fired furnace the other day. When I arrived I noticed that there was significant condensation in the flue exhaust and evidence of condensation dripping on the floor and onto the oil burner. The home owner had an AC system installed into the furnace this summer. The exhaust flue pipe goes up through the house, 2 floors, using B vent. The owner said the AC installer was coming back to replace all the damaged flue pipe, ( yeah, that will fix the problem,lol).
Not wanting to get involved in someone else’s mess. I left it at that, but was curious as to what would cause such a problem. Over sized system or improper placement of A coil in furnace.

[t527ed]

oil furnace into b vent?? do they make b vent for oil or should that be triple wall? condensation due to venting going up thru now cool house, warmer outside air condensing inside pipe. probably something causing a backdraft down chimney.

[jrc2905]

Everyone calls it B vent, the code calls for type L vent. Is it the same?
Mobile homes use roof jacks.

[oil lp man]

If it is stamped "B VENT". Then it is for gas appliances only. Only stainless steel should be used for oil. He should use triple wall or all fuel chimney.
And the chimney shouldn't be directly above the burner or anything else that would get ruined.
Also it should be properly sized to prevent condensation. If the pipe is oversized for the appliance it will condense. This is because the flue gasses can't fill the chimney fast enough, with enough heat, to escape before condensation occurs.
It is possible that rain has entered through a chimney cap that fell off. Or the cap is still on, but is subjected to driving rains.
The AC shouldn't have anything to do with the chimney as they are not direcly related.

[Edited by oil lp man on 09-16-2005 at 06:30 AM]

[jrc2905]

I never paid much attention to it, but now that I look, I have serviced 2 houses with oil fired heat that are using B vent for chimneys.
As far as this condensation problem, the customer said it only started when they put the AC in the house this year. I do not think it is water coming down the vent because it is crystallized all over the joints on the vent. Could it be a result of the vent going through the cold house causing the air in the vent pipe to condense?

[t527ed]

Originally posted by jrc2905
I never paid much attention to it, but now that I look, I have serviced 2 houses with oil fired heat that are using B vent for chimneys.
As far as this condensation problem, the customer said it only started when they put the AC in the house this year. I do not think it is water coming down the vent because it is crystallized all over the joints on the vent. Could it be a result of the vent going through the cold house causing the air in the vent pipe to condense?



you better START paying attention to it. you are the last one to service it your ass on the line if something bad happens. had one around here 15-20yrs ago house had been converted from gas to oil., b vent left in place. family bought house and when father came home next morning family was dead. acid from oil soot had eaten thru aluminum liner in b vent allowing fumes into house. many towns around here require heating certifications before house is sold or rented due to this case.

[jrc2905]

good point, never thought about all the oil to gas conversions that are going on due to the high cost of oil.

[casturbo]

Exhaust condensation typically means the flue gases are too cool to keep the moisture in vapor form, so instead they condense and makes drips. The boiler may have a burner problem such that the flame is much smaller, and thus, less hot, than it when the burner runs correctly. More than likely, the environment the furnace is in is much cooler. Or, the chimney pipe has an issue (liner rotted?). Or, it's rain water and the chimney cap is gone or leaking.

[t527ed]

Originally posted by jrc2905
good point, never thought about all the oil to gas conversions that are going on due to the high cost of oil.


oil to gas would not be a problem if oil was using triple wall with stainless inner pipe.just make sure flue is proper size ansd clean, then good to go. big problem is oil with double wall unless it has stainless inside which i have never seen.

[jrc2905]

Just to be clear this condensation problem is occurring during the AC season with the heat off.

[t527ed]

like i originaly said sounds like outdoor air inside pipe, cold outside. only other cause coud be backdraft pulling warm air down smokepipe. chek for negative pressure in house, maybe due to exhaust fan or leaky ductwork.

[oil lp man]

When he changes out the b vent. Make sure he puts in an approved chimney for oil, like triple wall. NO B VENT ALLOWED.
Then address the other problems.

[hvacjamie]

B vent. that's crazy.

[Edmund Forsthe]

it boils down to a couple of things the ho will not pay for the pipe change and the installers or the person who sold them the furnace or boiler did not size the unit right also a lot of ho's ***** abouth the oil consumption ive run into this many a times and the the boilers are being underfired ergo flue too cold all i can do is note it on the paperwork argue with the boss who always tell me just remove a couple of the baffles to accerate the venting.

[casturbo]

Originally posted by Edmund Forsthe
.....argue with the boss who always tell me just remove a couple of the baffles to accerate the venting.

You've done that too?....lol. Those stack temps really skyrocket with a few of those baffles missing, heh?