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I moved to a new house recently. The house is around 40 years old. It has a central heating system (natural gas furnace). I hear that one should replace the filter regularly (like once a month, or once every 3 months at least). However, I am unable to find where to replace it. I have attached a photo of the furnace area.

The furnace tag reads: frigiking, inc. Forced Air Central Furnace. Equipped for natural gas. Model no. UGI 80D8 E1.

There is a logo too on the furnace which reads Tappan Air Conditioning.

I have two questions:

  1. Does this furnace even require a filter, since I don't see a filter anywhere?

  2. If so, where is the slot where the filter resides? Should the filter be placed behind the vent screen right below the HVAC closet (see photo)?

HVAC unit and a vent below its closet

  • The existing filter might be placed behind the return below the closet. That is not a good position since the filter would be rather small and the air velocity rather high in that location. I have seen units with your setup where the filter was placed under the unit and accessed by removing the bottom return grill, which is also not good but better than placement at the grill itself. If the unit does not have any filter installed then the evaporator coil at the bottom will probably be in need of serious cleaning. – user39367 Jan 5 '17 at 15:32
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Your furnace definitely has a filter. To access the filter compartment remove the lower of the two metal panels on the front. The filter location is horizontal at the very bottom in the plane of the very bottom of the furnace. It will probably have a metal loop resting on it to keep it in place in the upward air stream. You may want to remove that metal loop to more easily put in the new filter, but it may be less trouble in the end to work around it.

(The upper panel is for inspecting and servicing the burner. This has nothing to do with the filter and you do not want to remove this.)

Before removing the panel turn the furnace off at the thermostat and at switch it off inside the closet if there is a switch there. Do not attempt to remove the access panel with the fan running. Carefully inspect the way the lower panel fits so you can return it to that state. You may want to have a new filter in hand so you can put it in right away.

To remove the panel grasp the top edge of the panel labeled TAPPAN Air Conditioning and move the panel enough to free it by pulling up, then work the panel out. It is a little tricky until you get experienced at it. The metal edge might be sharp. You might want to wear gloves until you are practiced at it. When you remove the panel you will see the squirrel-cage fan and the filter will be below that.

Using the standard grade of filter you might want to change the filter once a month or two or three. It just depends on how the filter is performing in your house. Here is a video showing the same type of furnace as you have, but I think you do not have to remove the upper access panel like this guy did. https://www.youtube.com/watch?v=cZknWY1zAUk

Our house is 45 years old and we have lived in it 39 years. Ours is a Carrier natural gas furnace of the same configuration as yours, but at installation 25 years ago I opted for an extra filter unit under the furnace which houses a 6-inch thick pleated paper filter. These are $25 to $30 each and I change it once a year. It is accessed through its own panel so it has been a long time since I opened the regular access panel.

The original furnace was of the same type and when we moved in the filter had fallen down and was lying on the bottom of the plenum below.

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    Some of the filters for these units are reusable. They are vacuumed and then washed, dried and replaced. The reusable type have a plastic or metal edging around the filter media. If a filter has a cardboard or heavy paper edge, it is not washable and reusable. If you want to use the cleanable type, you may want to alternate two of them. – Jim Stewart Jan 5 '17 at 11:49
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    The metal loop which holds the filter down can fit in with the curved loop inward (away from you) or loop outward (toward you). I think the latter is more convenient for replacing a filter. If you look at the rim where the loop goes you may find two holes where the ends of the wire are inserted. If they are on the back this would indicate that the loop is intended to face out toward the door. It may be that the loop is intended to just lie across the filter or the loop may tuck under a tab to securely hold the filter. – Jim Stewart Jan 5 '17 at 15:01
  • I did find the filter at the bottom of the lower compartment. Thanks. The video was really helpful too. – Nik Jan 5 '17 at 15:59
  • Was there a heavy wire loop holding the filter down? And if so were there any holes for the ends to fit in? You can undo the screws if there are any holding the white metal grill over the plenum, set aside the grill, and vacuum out dust and pet pet hair. I do that every 2 or 3 years (or 5 years). You don't need to shut off the furnace for that. Just don't get near the filter with the vacuum; it could rupture it. – Jim Stewart Jan 5 '17 at 16:15
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I moved into a brand new condo last year and thought to replace my furnace filter today. I have the same model of furnace (Lennox ml193uh) and could not believe I had to dismantle this thing just to find the furnace filter to replace it. You literally have to remove 4 tiny screws on the bottom of the furnace front and need a socket wrench to access the filter. Super painful and tedious especially for a brand new home and furnace.

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