Weird air filters inside the furnace

[beeth]

When I opened the cover of the furnace in the utility room at the basement level, the first time after I moved in to this house built year 2000, I was so surprised to find two air filters put right under the fan(please see the picture #1 below): one 16x25x1 old filter with dust, one old style of filter with plastic frame, both were held under a curved stick. What are they used for?? This doesn't look like a professional work.

In picture #2, the intake airflow is from the right side, through a 16x25x1 air filter(I changed it a few times after I moved in). Also, I noticed "20x25x1" was marked on the "base" of the furnace, but there is NO slot to insert the air filter like the slot on the right.

In picture #3, I lifted the filter a bit, I could see a big hole under the filters. I don't think it goes anywhere because the base sits on the concrete floor of the basement.

Should I keep it as is, or should I "fix" it? This doesn't look right to me.

Please advise. Thank you!!

Picture #1: two old air filters found *within* the furnace

Picture #2: filters within the furnace, cover the base and under the fan

Picture #3, air filter was lifted, a hole to the base

 

[WorthFlorida]

That plastic piece was shoved in there to prevent the fiber filter from getting sucked up. It looks like the covers are slipped into place and not screwed down, therefore lifting off the cover for a filter change would be the norm. The wire hoop, looks like its copper clad, is used to hold down the filter. The filter in there reads 16x25 yet one side is folded over. The back side might be cut to size. Just take a tape measure to be sure of the size that will fit. It's not uncommon in older installations to have air come in from two different directions. The side ductwork is a return and it is brought down to the bottom box and allows some of the air to flow up from the bottom? In the future when it is time to replace the unit, (add AC) besure the HVAC contractor does not reuse this setup. New furnace and AC air handlers rely more on a slower fan speed with a larger airflow for better efficiency. Most new duct work installed are larger than from past practices. After twenty year it might also be a good idea to have the plenum inspected and cleaned by a pro. Spider webs and dust can cause the burners to burn too rich and unevenly between them. In rarer cases the heat exchanger can rust through causing CO fumes to enter the living space.

One issue might be is to get enough air flow because of undersized ductwork, the fan motor may have been set to a higher or the highest speed speed and it can really pull in on the filters. Might be the reason for all the mess of the bottom setup.

 

[Sponsor]

 

[WorthFlorida]

 

[Reach4]

After thinking more on it, it seems to me that instead of a filter there, you may just want that bottom opening closed up with sheet metal. Your actual filter is one that is vertical.

Or if that turns out to be a suitable place for an extra filter (and if that is really earth down there I doubt that is a suitable place), get that modified to accept a standard sized filter. You would want a frame that lets you slide in a standard sized filter, I would think.

 

[SShaw]

After thinking more on it, it seems to me that instead of a filter there, you may just want that bottom opening closed up with sheet metal. Your actual filter is one that is vertical.

Or if that turns out to be a suitable place for an extra filter (and if that is really earth down there I doubt that is a suitable place), get that modified to accept a standard sized filter. You would want a frame that lets you slide in a standard sized filter, I would think.

If the "hole" in the bottom of the furnace really goes to the "ground" and not to another return duct, then it looks to me like that stand at the bottom of the furnace was built to allow airflow from the side and top. Looks like the side and bottom returns are connected by open ductwork. Some units require that to get enough airflow. In that case, you don't want to close off the bottom, as that would cause too much restriction, and could kill the blower motor, or cause too high a temperature rise in the furnace.

 

[Fitter30]

That plastic filter in the bottom looks like a electrostatic filter. Could just buy the correct size of plasti framed filter and mastic the box to the floor to seal. Pull the blower to wash the wheel ( remove motor before washing) if has central air might be able to up through heat exchange to see how dirty the coil is.

 

[beeth]

That plastic filter in the bottom looks like a electrostatic filter. Could just buy the correct size of plasti framed filter and mastic the box to the floor to seal. Pull the blower to wash the wheel ( remove motor before washing) if has central air might be able to up through heat exchange to see how dirty the coil is.

Yes, that's an electrostatic filter, I found a few in the house.
Are the filters used to seal to the ground? I attach another picture with a better view below:

 

[beeth]

If the "hole" in the bottom of the furnace really goes to the "ground" and not to another return duct, then it looks to me like that stand at the bottom of the furnace was built to allow airflow from the side and top. Looks like the side and bottom returns are connected by open ductwork. Some units require that to get enough airflow. In that case, you don't want to close off the bottom, as that would cause too much restriction, and could kill the blower motor, or cause too high a temperature rise in the furnace.

I attach another photo above, and I will check and confirm if the base of the furnace connects to the right duct.

 

[WorthFlorida]

The duct work looks fairly new and plenty large. The pictographs of the dirt on the filters show that air is coming in from the bottom.
I see there is an A Coil for the AC. That should be opened and check the coils. They can get clogged up with dust and lint that the filters missed. If the blower is loaded with dust so are the coils. There are coil spray on cleaners that require no rinsing. When the AC is running the condensation rinses the coils.

 

[beeth]

I confirm they are connected there is an opening between the furnace base(riser) and the bottom of the duct:

Why the airflow needs to go two paths instead of just one? I wonder why the bottom should be connected, why the airflow can't just go through the air filter(red one, 16x25x1, slide in) but also go from the bottom?

Should I replace the two old air filters inside the furnace, with one piece of right size filter? The base was marked 20x25x1, but I measured it's about 25x28x1 for full cover.
Or should I block the airflow through the base/riser/bottom(that is, leaving only one airflow through the 16x25x1 filter), by covering the base with a 25x28 sheet metal, or blocking the hole between the base/riser and the duct bottom?

Please advise. Thanks!

 

[WorthFlorida]

More air flow the better. The one side filter is too small and the installer realized this. If the bottom factory designed filter is 20" x 25" and the side is 16" x 25", that is 100 sq inches. Sometimes the furnace will sit on a much taller frame off the floor and then all the air can be drawn from the bottom. Nothing wrong with what you have.

I see from the picture you have some 18x18 fiberglass filters and it's why they are rated for 30 days. I know filter prices have been going up in the last few years where some get over $20 and that is crazy. The best money for the filter is ones rated at MERV-8 and are paper material. They are good for about 500 hours of use. I change mine every 90 days since my AC runs almost every single day. Home Depot brands don't use this rating so you'll need to compare. Try to shy away from those fiberglass ones for all they do is stop bowling ball size dust. If you search online there are some good buys that can be had. I buy 6 or 12 at a time. Last year at the beginning of the pandemic and shut down, paper filters were in short supply because paper were being diverted for masks, etc. and prices went up. Using MERV 8 rated filters you'll notice the dust levels in the home will decrease.

 

[WorthFlorida]

I know this is getting off topic but the picture is from my home after 90 days of filter use. Before and after MERV-8 filters. We keep our windows closed most of the time here in Florida. If the AC is not running, it's in heat pump mode. This past winter heat was on most of the time and I cannot understand where all that dust comes from. It's just the wife and I and 1/2 of the space is laminate and tile floors. Most cooking is done on the outside gas grill.

 

[Reach4]

I think the intention was that the horizontal filter would slide in and out of a space covered by a tan bottom front panel that has four hex-head screws.

 

[SShaw]

Could the slot be on side of the furnace?

Here is a screenshot from a York manual, referring to using 20x25 and 16x25 filter sizes. It says you need both side and bottom returns for CFM above 1800. It also says not to put the filter inside the furnace.

What is the size of your furnace, or the model number?

 

[Breplum]

It is indeed a sad installation.
It is common when the furnace airflow requirement is high, as in your case, that as SShaw notes, the mfrs require both side and bottom openings to be utilized.
That wire spring is normal for old-crap school, and used to hold a rigid filter into place in some cases.
The filter slot on the side is old, sloppy, leaky style, causing loss of conditioned air that you are paying to either heat or cool.
Modern standards call for air tight sealing of all points of entry. New furnaces even have cover panels that are gasketed.
You can get a shop to make up a cover panel and gasket them with peel and stick material from the hardware store for better efficiency.
Also to note: The condensate from AC coils is supposed to be trapped so that you aren't blowing air through the 3/4" pipe to the outdoors.
Some time soon, get yourself a 96+% AFUE furnace. You will save bucks in the long run on heating fuel and make sure you hire a contractor that actually has knowledge and ability to do the job to the highest industry standards.

 

[beeth]

Could the slot be on side of the furnace?

Here is a screenshot from a York manual, referring to using 20x25 and 16x25 filter sizes. It says you need both side and bottom returns for CFM above 1800. It also says not to put the filter inside the furnace.

What is the size of your furnace, or the model number?

Thanks for WorthFlorida and SShaw pointing out the filter type, so what type of filter should I buy for the "bottom" one to replace the existing mess one? I used 3M Filtrete "7"(1000) 16x25x1 for the side one.

The model number of the furnace is York P3HUC16N09201C.

Please advise. Thanks!

 

[beeth]

It is indeed a sad installation.
It is common when the furnace airflow requirement is high, as in your case, that as SShaw notes, the mfrs require both side and bottom openings to be utilized.
That wire spring is normal for old-crap school, and used to hold a rigid filter into place in some cases.
The filter slot on the side is old, sloppy, leaky style, causing loss of conditioned air that you are paying to either heat or cool.
Modern standards call for air tight sealing of all points of entry. New furnaces even have cover panels that are gasketed.
You can get a shop to make up a cover panel and gasket them with peel and stick material from the hardware store for better efficiency.
Also to note: The condensate from AC coils is supposed to be trapped so that you aren't blowing air through the 3/4" pipe to the outdoors.
Some time soon, get yourself a 96+% AFUE furnace. You will save bucks in the long run on heating fuel and make sure you hire a contractor that actually has knowledge and ability to do the job to the highest industry standards.

Thanks breplum! Could you please tell me a bit detail about:

1. "shop to make up a cover panel and gasket them with peel and stick material from the hardware store for better efficiency": did you mean how to cover the filter slot on the side(the leaky style)? or should I simply tape it with HAVC tape? Please tell me a bit detail about the "cover panel" and "gasket"

2. "The condensate from AC coils is supposed to be trapped so that you aren't blowing air through the 3/4" pipe to the outdoors", sorry I don't understand this, can you explain the detail, like show me in the picture?

Thanks again!

 

[beeth]

The duct work looks fairly new and plenty large. The pictographs of the dirt on the filters show that air is coming in from the bottom.
I see there is an A Coil for the AC. That should be opened and check the coils. They can get clogged up with dust and lint that the filters missed. If the blower is loaded with dust so are the coils. There are coil spray on cleaners that require no rinsing. When the AC is running the condensation rinses the coils.

You also mentioned about the AC coils like breplum said today, could you please tell me a bit more? Sorry I am not familiar with this but love to learn. Thanks again!

 

[WorthFlorida]

Filter size is what fits and type is whatever you like and can afford. As posted by Reach, the frame bracket at the very bottom can be removed by the four screws and a filter may slip into it. Give it a try.

With a mirror look inside the blower wheel and check to see how much crud is caked on to the fins of the blower. After twenty years it is probably loaded even with proper filters. Just normal stuff. To remove it, of course turn off power at the breaker, move all of those wire out of the way, undo four or six screws hold in the blower frame, then it can slide out, housing and all. But the way it is wired and what looks like something was added, that black box suspended, I'm not sure what that is. It looks all too tight to remove the blower.

Very common for forced air systems to have the A coil sit on top of the furnace with a hand made sheet metal as a housing. My house in Syracuse, NY was this way. Access doesn't look easy. Might be a panel on one of the three sides that can be removed for inspection.

These might be beyond your skill sets. That motor housing is a lot heavier than it looks and dropping it on removal is not a good idea. And don't do the coils if you can't get easy access. If you never had the AC checked out with gauges, it be a good idea to get it serviced before the heat hits. They're not that busy at this time of the year but the first hot day, it could be days before someone can get there.

The heat exchanger should also be looked at. With the cover off you can vacuum and or blow out dust and spider webs around the air flow adjustments. There are plenty of You Tubes on this subject but don't be in a rush to change anything on the air fuel mixture. For the most part these never need changing once it's set up.

I bought my first house in 1979 and there was no home computers let alone the internet. I got articles and books on these subjects and learned, but one time I burned out a blower motor, dummy me. Education is not cheap.

 

[beeth]

Filter size is what fits and type is whatever you like and can afford. As posted by Reach, the frame bracket at the very bottom can be removed by the four screws and a filter may slip into it. Give it a try.

With a mirror look inside the blower wheel and check to see how much crud is caked on to the fins of the blower. After twenty years it is probably loaded even with proper filters. Just normal stuff. To remove it, of course turn off power at the breaker, move all of those wire out of the way, undo four or six screws hold in the blower frame, then it can slide out, housing and all. But the way it is wired and what looks like something was added, that black box suspended, I'm not sure what that is. It looks all too tight to remove the blower.

Very common for forced air systems to have the A coil sit on top of the furnace with a hand made sheet metal as a housing. My house in Syracuse, NY was this way. Access doesn't look easy. Might be a panel on one of the three sides that can be removed for inspection.

These might be beyond your skill sets. That motor housing is a lot heavier than it looks and dropping it on removal is not a good idea. And don't do the coils if you can't get easy access. If you never had the AC checked out with gauges, it be a good idea to get it serviced before the heat hits. They're not that busy at this time of the year but the first hot day, it could be days before someone can get there.

The heat exchanger should also be looked at. With the cover off you can vacuum and or blow out dust and spider webs around the air flow adjustments. There are plenty of You Tubes on this subject but don't be in a rush to change anything on the air fuel mixture. For the most part these never need changing once it's set up.

I bought my first house in 1979 and there was no home computers let alone the internet. I got articles and books on these subjects and learned, but one time I burned out a blower motor, dummy me. Education is not cheap.

Hi WorthFlorida, I really appreciate all the info you provided here. Sorry I read that several times but I still don't understand what's the current problem(s) you discovered other than the air filter issue(which needs to be replaced). You mentioned about the A coil, then curd inside the blower, and checking the AC with gauges, could you please tell me the current problem(s) a bit easier?

About the air filter, do I need to go with certain FPR or MERV number? I wonder if I buy those more expensive ones(filter better for tiny particles) it could block the airflow with inappropriate pressure.

Also, I noticed that the house got much more dust than my last house(both built year 2000) after I moved in 2 years ago, I would guess the current filter issue may be one of the reasons, but if you think that could be something else, please advise.

Thanks again!