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Here is the back story:

  1. Starting to finish basement, needed to exhaust my furnace outside instead of drawing in air for combustion inside the house. Hired HVAC person to do this in the fall.
  2. Winter arrives, I go to run furnace, first really cold day and the furnace won't start up (an Armstrong Air unit) that is 8 years old. Error codes tell me: "pressure switch open with inducer on".
  3. I call up same HVAC person. There is no report, but he determines that my exhaust motor is the culprit. It is replaced. They do not replace the pressure switch or give me any diagnostic reports or paper work. The repair costs me $600 (that is the cash deal). Tells me that it includes parts warranty and labour warranty for a year and to call him if it happens again.
  4. Furnace starts running for 10 more days. Gets really cold again, and furnace stops working again with the exact same error code. Same HVAC repair person comes back and tells me that my heat exchanger is cracked without opening anything up within 20 min of being here (based on the flame at the burner) and tells me the entire furnace needs to be replaced.
  5. He leaves with the furnace running again after simply disconnecting the air intake pipe from outside, saying I can leave it off until I decide on which new furnace I want to install and gives me the fear mongering talk about CO2. He also wants to sell me a refurbished furnace that he has, or offers to sell me a new Payne unit which seems to have a less than desirable track record.

I have come to the conclusion that this guy has taken me for a bit of ride and overcharging me for the service (which I confirmed with another reputable person in town asking me to quote the same work), and he also didn't necessarily honour his warranty after charging me another

I ended up putting a shop vac on the end of the intake pipe (disconnected) and blew some hot air through the tube from the outside to melt any ice or snow inside for about 10 min and made sure there was no obstructions. I reinstalled the intake on the furnace and the furnace seems to be running fine right now.

I know these Armstrong furnaces are not the most reliable, but I would like to get an opinion to see if there is anything abnormal about the flame that would indicate a cracked heat exchanger. There looks to be a bit of rollout during the initial ignition, but beyond that, to my untrained eye, it flames seem to be fairly concentrated through the openings and not like the examples of rollout I have seen online. Here is a video of the startup sequence of the burners.

https://youtu.be/3zoq5lxpHGk

Any thoughts?

  • 2
    Can you get a 2nd HVAC person in there with an actual combustion gas analyzer and manometer to check the performance of the exhaust/flue system? – ThreePhaseEel Dec 28 '17 at 1:12
  • That is what I would like to do. They said for $150 they can do a diagnostic and check to make sure there are no gasses leaking and determine health of the unit. In the short term, he said he would take a look at my video but I haven't heard back yet and wanted to get some opinions online of the video. The furnace seems to be running great right now, and still connected to the outside air intake. The 2nd HVAC guy told me that he suspects if the 1st guy was serious about the unit needing to be replaced and the heat exchanger being cracked he would have red tagged and condemned the unit. – nspace Dec 28 '17 at 1:27
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    It's hard to say for sure based just on the video, but the flame does start dancing around when the blower comes on. – Tester101 Dec 28 '17 at 13:42
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    I don't see anything abnormal. Most likely you had ice/snow in your venting. That said if the guy you had out didn't hook up a combustion analyzer, or a manometer, you would benefit from having someone out to check the unit, especially the HX with proper diagnostic practices. And I wouldn't use the previous again, based on what you described here. Seems in too much of a hurry to go through the checklist of items that MAY cause the issue you experienced. – Jim Dec 28 '17 at 16:08
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First off I did not see anything in the video to make me think there was a cracked heat exchanger. The heat exchanger may be cracked but the video does not indicate so. It seems that removing the inlet pipe fixed the problem? The furnace installation instructions has vent tables showing what size pipe can be used for various lengths and amount of elbows. For instance a 90,000 btu furnace can have a maximum of 70’ of pipe and 4 elbows with 3” pipe but only 20’ of pipe and 4 elbows with 2” pipe. And this is combined for both pipes, not for each pipe. So adding the second pipe may have pushed you over the limit. This furnace comes with a restriction plate that must be installed if using only 1 vent but must be removed if using 2 vents. Was it removed? And in my experience these tables are often over generous. I have pushed the limits of the tables and have had venting problems. I had to either increase pipe size or reduce the amount of elbows or both.

  • That is really interesting that you commented on the pipe length. The exhaust pipe (which was previously installed) has about a 15 ft +/- run with 2 x 45 degree elbows to get to the exterior wall. The new intake pipe the same tech put in has about the same length of pipe to get to the wall, plus a couple more feet, and 3 sweeping 90 connectors. The pipe is 2" IPEX system 636 on this. I actually ended up redoing his work and replaced accomplished the same thing using 2 x 45s and less pipe. It definitely seemed to help. – nspace Jan 7 '18 at 13:45
  • There was a grill on the pipe before he removed it and added the intake pipe. Would that be the restriction plate you were mentioning? I assume that is a metal grill that stops larger debris from being sucked, but also simulates some of the friction from having a pipe attached? – nspace Jan 7 '18 at 13:47
  • I am guessing this is a 50,000 btu furnace based on the video. Your description sounds like it is within specifications. With 2” pipe and 20 feet of length you are allowed 6 elbows. What goes on when it exits the building? Any weird bends or restrictions? You should make sure there are no restrictor plates left on the furnace. Round plastic disks with a bunch of holes punched in it. Should be right at the furnace. – user76730 Jan 7 '18 at 18:17
  • Venting tables are usually pretty good but as part of commissioning a new furnace I always hook up a magnahelic gauge to the pressure switch to make sure the pressure does not exceed the rating of the pressure switch. Found this the hard way when the tables were actually wrong, they got amended shortly after I had a very unhappy customer. – user76730 Jan 7 '18 at 18:21
  • Here is the before (what the tech did) and after the more efficient reroute that I did inside the home: imgur.com/a/2UDPO Here is is outside: imgur.com/a/EnEOj One of the issues with this placement, is that the warm air from the exhaust is freezing on my intake and building up and tripping the switch. I ended up taking a heat gun to melt the ice and used a shop vac to make sure the pipe is clear. I now have a small piece of plywood to separate the exhaust from the intake. Ever since doing this, there has been no ice build up on the intake. – nspace Jan 7 '18 at 21:05

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