My schooling for ministry did not include HVAC training. Yet it seems that more and more of my time lately has been spent trying to get the furnace to heat the sanctuary properly.
Actually, the furnace is most likely working exactly as it was designed to work, in that a "fail-safe" part of the furnace that is designed to make sure that the exhaust from the natural gas vent doesn't get back into the building keeps activating and shutting the furnace off. We've had a professional HVAC company come out to look at the situation twice (at about $90 per service call with the the first call lasting about an hour and the second lasting about 10 minutes) over the past month or so, and both of the people who came out agreed that the issue seems to be related to the exhaust pipe.
This system has been in the building since before my 2004 arrival as the congregation's pastor. We have had some issues with this situation in the past few years, and have been told by professional HVAC people that it is likely that the PVC exhaust pipe leading out of the building was too close to the outside part of the air conditioning unit for the same furnace/air conditioner; the pipe was emitting exhaust directly towards the a/c unit, which is only about 2-3 feet away from the PVC exhaust pipe opening. The diagnosis was that exhaust from the pipe was hitting the a/c unit and swirling the gasses in such a way that the "fail-safe" was being activated because it sensed gas still in the pipe. It was suggested that we re-direct the exhaust away from the a/c unit.
Rather than pay inflated prices to HVAC people for them to extend some piping, we decided to try to do it ourselves. The first fix included attaching about 8 feet of corrugated pipe to the end of the PVC pipe and re-routing the exhaust away from the a/c unit. This seemed to work fairly well, until this past Wednesday evening. Suddenly, the furnace shut off and the indicator lights on the furnace showed the same problem--that the "fail-safe" had kicked in again, most likely again due to blockage in the exhaust system. This is when we made our second call to the HVAC people, and this person told us that the corrugated pipe was not a good solution, as the pipe was letting water from condensation build up in the pipe, thereby blocking the gasses from flowing out of the pipe, and making the "fail-safe" kick in. The HVAC person lifted the 8' tubing up and about a gallon of water came out. He told us that corrugated pipe was not a good idea, but rather that it had to be smooth, like a PVC extension. He suggested an extension that went over the approximately 4-foot tall a/c unit.
So yesterday, we extended the PVC pipe up to about 2-3' above the a/c unit (Thanks to Jimmy and Charlie for working on that!). But this morning when I got to the building, the furnace "fail-safe" had again kicked in, and the sanctuary temperature as of about 7:45a.m. was only 60 degrees. We noticed that the new PVC pipe had an elbow joint on the end which was facing downward. We thought about this, and decided that perhaps the exhaust gas was rising back up into the pipe. So we therefore took a hacksaw to the end and made the end of the pipe vertical again (pointing out away from the building)--the way it had been prior to adding the extension (only now considerable above the a/c unit, and directed on a 45-degree angle between the a/c unit and the building). This was at about 8:45a.m., and the furnace now seemed to be running properly--until about 11:00a.m. or so, when the "fail-safe" kicked in again.
We are at a loss as to what to do next. Someone suggested that by adding the approximately 4' of PVC pipe going up that condensation may be collecting in the bottom of the pipe (even though re-routing the PVC over the a/c unit was what the most recent HCAC person said was needed). We have considered drilling a small hole in the bottom of that PVC to let any collected condensation water drain out the bottom, but we don't know if this is a viable alternative or not.
We don't want to call the HVAC people out again, and have them charge us yet another $90 to tell us what we already know--that the "fail-safe" is kicking in. What we are looking for is someone with some knowledge in this area who might be able to give us more advice. As I said, they did not teach HVAC in my ministry training, so I am open to (and hoping to get) some suggestions. Please feel free to offer any suggestions by commenting to this post.