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In an addition in my house before I moved in, a second furnace was installed way up on crawl space. The furnace is a Carrier Weathermaker 9200 and it was installed sideways (really 90 degrees counterclockwise from a normal standing position) just for perspective.

I called up the company that installed it way back when and while they still do exist they no longer travel to my neck of the woods so they can't come out to talk about the installation if their notes were even detailed enough and still kept from the installation.

But I had the instruction manual and so I was able to take off the front cover and then the cover for the area where the filter would normally be (as stated by the instruction manual). Now my other furnace uses disposable filters and I know what they look like. But for this one, I would imagine that they would use a reusable filter. When I open up the compartment, I don't see anything I would call a filter.

It is possible that based upon requirements of the space I suppose that the filter could be relocated to another part, but again looking over the unit, I don't see where that would be. According to the manual page I am posting, it should be #8, and I have a clear picture of that region.

Can you please tell me if you see a filter, and if not, where there might be one for this model?

Manual Page Supposed to be location Zoomed out view with cover back on Left side of unit zoomed in Ceiling Kitchen Filter Sun Room High Wall Filter

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    Filters are not usually inside the furnace cabinet. Look for an access panel in the main return air trunk. – isherwood Feb 25 at 16:08
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    Can you get a photo of the larger area surrounding the furnace? The filter is very often built into the return air ductwork, not the furnace itself. – PhilippNagel Feb 25 at 16:08
  • @PhilippNagel I will get it later today when I am back up there. There are 2 vents that have air from that side of the house come in that do have disposable filters. Could that be a possible configuration: nothing at the furnace itself, but only at the exit points where the hot air travels to? – demongolem Feb 25 at 16:27
  • I should also note that everything is so very tight because it is crawl space. So unlike my other furnace which is in my basement and you can walk around 360 and observe everything, it is a little hard to move around and get good angles for this one. – demongolem Feb 25 at 16:31
  • It's possible that they could have placed several filters instead of just one, but they should be at the return intakes, not at the outlets. The filter is there primarily to protect the furnace innards, not the air in your house. – PhilippNagel Feb 25 at 16:32
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Your filter is in the return vent in the wall. Look at photo #5 in your post and you’ll see the markings of a 12x12x1” filter. Flip out the two tabs at the bottom and the grill should swing out to allow you to change the filter.

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  • I do change these 2 filters in the photo every 90 days, so if that is all there is to my system these 2 points, then I am good on my filters. The reason why I was concerned by this whole thread is not heat output of my furnace, but because the air quality in my Sun Room (the Kauai photo) seems to be a little bad even with changing that filter. I am trying to identify at what point in the setup there could be buildup of the dust, the spores, the mold which could be causing it. If there is no filter at the furnace I am happy, because it is a pain to get to. – demongolem Feb 25 at 19:34
  • @demongolem As long as there is a filter in all return vents and no significant air leakage in the return system, there is no difference between vent filters and filters in the furnace itself. In fact, this is better because it keeps the return ducts clean. – DoxyLover Feb 25 at 19:39
  • I fully agree and this is my preferred method of installing filters more intakes in multiple rooms also assists in overall air flow and balance. The new photos have been helpful to see what you have. – Ed Beal Feb 25 at 20:20
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I do not see a filter and would not expect it to be in the attic.

I don’t like filters in restricted access spaces so in the case like yours. I will put a 14x20 on the intake(s) that fits between studs or joists and is accessible from the living space.

The filter needs to be on the intake because they filter out dust and debris that will get stuck in the heat exchanger and cause early failure of the system on top of being inefficient.

I have been asked; which are the intakes? Normally flat grids and if you place a sheet of paper or newspaper up to them while running it will suck the paper to the grid, (don’t leave it blocked it’s not good for the system.

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  • I have added where the 2 disposable filters are. They are both high up and not going to be blocked anytime soon. The two major rooms serviced by this filter are the Dining Room/Kitchen and the Sun Room and they each have a filter. Are these the intakes you are talking about? – demongolem Feb 25 at 18:17
  • In any event, when I was up there today after opening the cabinet it was filthy (with possible mold) and needed a good clean. I suppose some maintenance is in order, even if a filter is not necessary in the furnace for my setup. – demongolem Feb 25 at 18:21
  • Very possibly those could be intakes, my last home I had 2 upstairs in the girls living room and dining area and 2 down stairs in man land, all the grubby construction guys downstairs and lady’s upstairs and it did not make much of a difference they all needed changing about the same time. If you don’t protect the heat exchanger it may not last as long because of the build up of dust. As you found dust that got moist and mold started growing a possible health hazard. – Ed Beal Feb 25 at 18:57
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The #8 in the manual references a metal rod that holds the filter in place. Putting a filter there would do no good unless the intake was on the other side of the filter. Your intake appears to be on the top of the furnace. Your photo is not light enough so I can't see if there's any mounting holes for bracket #8. Take note of how #8 is mounted in the blower cabinet, are there similar holes on the top portion of the cabinet? If so you would put the filter on top and move bracket #8 to hold it in place. The installer may have put the filters in a more convenient location elsewhere in the house so you need to determine that otherwise they'll clog up and you'll have problems.

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    Although it is dark I can see that the washable filter that came with your furnace was not installed. You can see right into the return duct at the top of the 2nd picture! The disposable filter in your 5th picture was installed instead, so that you would not have to crawl into the attic every month to remove, wash, and replace the filter. – jay613 Feb 25 at 19:16

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