Ken Bates
01-15-2009, 10:36 AM
The specific warm air, gas fired furnace is sold as CONCORD and made by ARMSTRONG. It is 6 years old. It is a 90% efficient condensing unit. I guess the type is called up-flow (circulated air) and down-draft (exhaust gases induced down by a motor driven fan to an area where the condensate drains out and then exits upwards via PVC exhaust vent to the exterior.)
The 2 part heat exchanger consists of 4 ferrous steel clamshells on the top and stainless steel tubing at the base for ultimate heat extraction and condensing the water from the combusted methane gas.
My only vantage point is via a 5X11 inch removable register cut into the plenum. I use a large glass mirror to view the exchanger. Everything looks clean and brand new.
THE PROBLEM: My nose and my Tif combustible gas detector say something is wrong. The odor is best described as the smell you get when book (paper) matches fail to fully ignite. Sort of a Sulphur-like odor. Slightly acrid. A reliable CO detector shows nothing. It does show about 25 ppm at a test port drilled into the exhaust pipe a few inches above the furnace vestibule. Also, this burnt match odor cannot be detected when I smell the exhaust exiting from the vent on the exterior.
OBSERVATIONS: I once saw a small spot of liquid on the floor pan of the blower compartment. As time goes on there are white, hard deposits accreting on the floor pan and in other areas. It appears that a liquid is dripping down from the heat exchanger area into the blower chamber. Also, some have made their way out of the plenum and dripped down the exterior part of the plenum where a flange was created to attach the plenum to the furnace cabinet. ( The humidifier is not attached to the plenum and is downstream on the main duct supply trunk and we do not have hard water with minerals and the problem occurred without water in the humidifier.)
Simply said it appears that condensate is escaping and then being blown upwards and also evaporating and then leaving a hard white residue. However, I have taken an ounce of condensate and evaporated it and found no residue. The strong smell seems to occur at first firing in the morning (the t-stat is lowered at night)
I once got to speak with an unfriendly Armstrong tech person who burbled something about a coating applied to the interior of heat exchangers. Anyone have any ideas? I have consulted a highly rated HVAC company and they found nothing. I suspect a seal failure where the round stainless exchanger tubes connect to a manifold that separates gas from condensate. But I have never seen this part of a furnace. This area is not visible or readily accessible. $1,200 to dismantle the furnace to get at the exchanger. The clamshell is very visible and looks perfect. No stains or white deposits on it, however, my theory is the very hot clamshell is evaporating the mist that is coming from a leak below and carries something dissolved in it that smells like half burnt book matches.
The 2 part heat exchanger consists of 4 ferrous steel clamshells on the top and stainless steel tubing at the base for ultimate heat extraction and condensing the water from the combusted methane gas.
My only vantage point is via a 5X11 inch removable register cut into the plenum. I use a large glass mirror to view the exchanger. Everything looks clean and brand new.
THE PROBLEM: My nose and my Tif combustible gas detector say something is wrong. The odor is best described as the smell you get when book (paper) matches fail to fully ignite. Sort of a Sulphur-like odor. Slightly acrid. A reliable CO detector shows nothing. It does show about 25 ppm at a test port drilled into the exhaust pipe a few inches above the furnace vestibule. Also, this burnt match odor cannot be detected when I smell the exhaust exiting from the vent on the exterior.
OBSERVATIONS: I once saw a small spot of liquid on the floor pan of the blower compartment. As time goes on there are white, hard deposits accreting on the floor pan and in other areas. It appears that a liquid is dripping down from the heat exchanger area into the blower chamber. Also, some have made their way out of the plenum and dripped down the exterior part of the plenum where a flange was created to attach the plenum to the furnace cabinet. ( The humidifier is not attached to the plenum and is downstream on the main duct supply trunk and we do not have hard water with minerals and the problem occurred without water in the humidifier.)
Simply said it appears that condensate is escaping and then being blown upwards and also evaporating and then leaving a hard white residue. However, I have taken an ounce of condensate and evaporated it and found no residue. The strong smell seems to occur at first firing in the morning (the t-stat is lowered at night)
I once got to speak with an unfriendly Armstrong tech person who burbled something about a coating applied to the interior of heat exchangers. Anyone have any ideas? I have consulted a highly rated HVAC company and they found nothing. I suspect a seal failure where the round stainless exchanger tubes connect to a manifold that separates gas from condensate. But I have never seen this part of a furnace. This area is not visible or readily accessible. $1,200 to dismantle the furnace to get at the exchanger. The clamshell is very visible and looks perfect. No stains or white deposits on it, however, my theory is the very hot clamshell is evaporating the mist that is coming from a leak below and carries something dissolved in it that smells like half burnt book matches.