Overheating Furnace Question

[supersurgilator]

My parents have a 1999 Amana furnace (Raytheon made not Goodman). About this time last year it started overheating and the burners would shut off on overload. We had a service tech out to look at it and he said it was just plugged filters. (Never in my life have I had a furnace do this as I've always kept up on top of that for them). He cleaned the furnace out and changed the filters and it was fine. Everything has been fine this year and I changed the filters for them the end of November. 3 weeks later, I noticed the burners cycling off again. I was like there is no way they are dirty again. I went and pulled them and they were covered in this strange substance. It was like dust, but mixed with something and it was coating the whole filter. I changed them again and this weekend it started overheating again. I go and check the filters and once again I can see they are visibly coated with something, this time they had a grayish tint to them. These are the same filters I've used in their furnace for years, DuPonte pleated filters from Menards. I always used to get 3-4 months out of these filters so the fact that they are now getting clogged every 3 weeks just doesn't make sense to me. Like my mom said the only difference is they have been running a humidifier. Do you think that extra moisture in the air would cause that? Something just doesn't add up and its bugging me!

 

[yogitunes]

some filters are too dense for furnaces....

I know we could not use the 3M HEPA filters during the Summer as the A/C would freeze up from low air flow....during those months had to use the cheap blue fiber ones...

is it also possible the Air Ducts need cleaning?.....

 

[tomturbomatic]

Are they using distilled or demineralized water in the humidifiers? They could be clogging the filters with a fine mineral dust if they are using tap water. I had a West Bend humidifier with the slowly rotating drum with a foam filter on it and it put mineral dust out unless the fan was at the lowest speed unless I bought distilled water.  Friends in FL had the reverse with too fine a filter causing AC to frost up. Make sure they are not using an oil-based air freshener which could be combining  with the mineral dust. This season's filters could be tighter than last season's

 

[gansky1]

I use the lower-end pleated filters year-round, change them every 4-6 weeks.  The first 3M super-filter I used many years ago caused the A/C coil to freeze within a few days.  Neighbor is an HVAC engineer, said my system can't handle that dense filter material.   Summer season the filters are grayish-brown since we live on the edge of the Dustbowl, this is normal.  Winter, we have a whiteish dust on the filters, no doubt it comes from the humidifier I have on the furnace. 

 

[sudsmaster]

The other thing to check is that there may be a filter hidden inside the plenum for air return to the furnace. At least that was the case in my house. Since there were already filters at two return registers on the floor of the living quarters, I simply taped over the ends of the slot for the extra filter down in the crawl space. Furnace works fine without that extra filter (it was a cheap spun glass type anyway).

But it does sound like the humidifier might be the culprit. I'd also be concerned that the gray matter on the filters now is some sort of mold or fungus.

 

[DADoES]

 
I've used the orange Filtrete 800 for some years, hasn't caused any issues.