Marty Singer is one of the few NCI trained in Carbon Monoxide safety and combustion analysists in our area. The “only” way to know if your furnace is safe and efficient is for a trained technician to measure the carbon monoxide oxygen and temperature of the flue gas. A blue flame only indicates that the furnace is operating. It doesn’t mean that it is safe or efficient.
The above image shows the heat exchanger of a 1 yr old furnace that a competitor installed. The black sooted section is the junction of the primary and secondary heat exchanger with the cover removed. The sooted sections of the heat exchanger were not visible with the heat exchanger installed. A visual inspection of the assembled furnace would not have revealed this condition.
I was called to preform maintenance check. The homeowner had no idea that there was anything unsafe about his furnace. The flame was blue, but the carbon monoxide in the flue gas was in the thousands of ppm. I know this because I measured it with a combustion analyzer that I calibrate with laboratory test gas. The vent motor’s air pressure safety switch did not open to shut off the furnace. This is because that pressure switch is intended to detect a blockage in the vent pipe after the draft motor. A blockage before the draft motor increases the negative pressure needed to close the air pressure switch.
Modern furnaces have many well thought out safety features, but they cannot be soley relied upon to protect you.
The propane conversion kit was not property installed. Parts were missing and not adjusted correctly. This furnace was unsafe. It was red tagged until repairs could be made.
Below is a link to download a pdf file that you want to see if you have an older Carrier, Bryant or Payne condensing gas furnace. It also goes into much further details and studies on the topic of furnace safety and the need for combustion analysis to be performed during annual maintenance.
The image above shows post repair testing of the aforementioned sooted up furnace.
Flue gas Carbon monoxide is down from thousands of ppm, prior to repairs, to just 4 ppm after repairs.
This furnace is safe, efficient, delivering its rated capacity and operating at the optimal temperature rise.
Anyone not testing is guessing with your safety and investment.