Magic-Pak Furnace mystery smell...


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Old 02-18-18, 08:36 PM
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Magic-Pak Furnace mystery smell...

I live in a building that was completed two years ago. I am the first person to occupy my unit. I have a Magic-Pak combo gas furnace and air-conditioner in my unit. Since the beginning, it has consistently exhibited a strange bitter/burnt smell from all of the registers after the heat runs for about 10-15 minutes. It seems worse the longer the furnace runs. It does not happen with the fan on (no heat or ac) or the air conditioner alone. I have had three different contractors out who tested for CO, temperature, gas leaks, evidence of melting wires/insulation, blower and exhaust motor voltages, inspected the heat exchanger, gas pressure, etc. The smell originates in the furnace, but nobody seems to be able to figure out why it happens.

The following has also been done:

The Honeywell gas valve was replaced when the unit was first installed because it had a gas smell after it lit. This is different than the current smell and was solved by this replacement as far as I can tell.

The furnace blew the circuit breaker and shut off once (that I know of). But when the breaker was reset it worked fine again.

The last tech that was out said that the furnace blower motor intermittently wasn't responding to the auto turn on signal from the board/thermostat while he was doing the inspection. He recommended the board should be replaced because it might not be working reliably. No suggestion that this might account for the odor.

There are spring loaded fire/smoke dampers on the registers in this unit. Two of them triggered for some unknown reason when I wasn't home. There is no evidence of fire or smoke (other than the mysterious odor from the furnace).

The filter has been changed multiple times. The filter that came with the unit is a "hog hair" filter that didn't look like it would filter anything. It was replaced with a 3M pleated filter. The furnace makes this smell regardless if the original filter is used, the 3M filter is used, or no filter is used. There was a decent amount of dust collected in the furnace (presumably due to the hogs hair filter being ineffective) and this was wiped out without an impact on the smell.

Has anyone had a similar experience with these furnaces? Suggestions?
 

Last edited by asus389; 02-18-18 at 08:53 PM.
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Old 02-18-18, 09:34 PM
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I am not an HVAC specialist, but I do have a brand new Magic-Pak and, though it never blew any fuses or tripped any breakers, I did experience a burnt smell for maybe 2-3 months after I started using heat. No smell with AC or with just the fan on.
In my case, it was the silicone mastic used to seal the ductwork connected directly to the unit. Inevitably, some of it can always end up in the ductwork interior. If they used this grey caulk on your ductwork and if this is the first time heat was applied to it, it could be just that. Takes quite some time to outgas, unfortunately. This was the first suggestion by my HVAC folks and it turned out to be the case -- the smell just gradually disappeared.
 
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Old 02-19-18, 09:18 PM
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Thanks. How can I tell if they used Mastic to seal the ducts?
 
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Old 02-19-18, 10:07 PM
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Can you maybe post a few photos of the ductwork hooked up directly to your unit? HVAC folks here may be able to recognize it. In my case, it's basically this grey goo.

I actually did an experiment: I peeled a tiny bit of that mastic, put it into a teaspoon & heated it. The smell matched right away.
 
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Old 02-19-18, 10:35 PM
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Yep..... a gray goop that looks like putty or real thick paint.
How-to-insert-pictures
 
 

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