I have an older Rheem furnace and would like change the filter. Appreciate any help for me to know what the correct filter is and where it is to be placed. Also, if anyone has a manual or instructions for this model or know where to get one - that would be very helpful.

I tried the Rheem site but my serial number is 15 positions and didn't match the types it listed.

Again thank you.

 

Welcome to the forums.

I don't recognize that model number.
The full model number can be found on the side wall inside near the burner.
Typically it will be a long number.

Many units don't come with a factory filter location and the installer will add on a filter box.
The filter needs to be between the return ductwork and the furnace.

Pictures of your unit can also be very helpful.... How to insert pictures.

 

Here's some photos:

First is a photo of the Rheem furnace information plate. From what I can see by increasing the size of the photo, the plate has the model number 3600-80AD, Serial number looks like CN4D106 F5275 4094


Second photo is of the furnace system



Third picture is a close up of how I found the filter sticking out


Fourth photo - I did see this sign about filters must be installed external to the furnace casing but didn't know what it meant


Fifth picture - picture of a vent - not sure what this vent is for. Is it for fresh air intake? There is an air intake in the house and also floor vents for warm air to circulate in the house Is this to exhaust the air from the furnace combustion ?



The system is old but it works - heat is produced. Wanted to change the filter and went under the house to check it out.

Again, thanks for looking at this.

 

With the dust on that register it looks like a return.
Air back to the furnace. There should be more returns.

That note means that there is no filter inside the furnace and that Rheem has not supplied a place to put it. The installer added a filter area external to the furnace.

You have a 20"x25"x1" there.
You're going to have to measure the height and width of the housing.
20"x20"x1" is the nearest factory sized to yours.
Based on your measurements you made need to get a custom filter size like 21" tall

 

Ok, thanks, I think I understand how this works better now. Please correct me where I don't have it quite right.

The Rheem furnace is in green and it is located to the left of the galvanized metal box which must have been put in by the installer for the filter and it looks like it is the place for the air coming from the return in the house - we
have an air return (I called it an air intake in previous post) inside the house - the return grill is large and on the wall of the hallway.

So that grill in the picture is another return for air into this galvanized metal box which connects with the duct for the return with air from the house above.

I have a question on this air return under the house. Is that normal?

Is it ok for an air return to be under the house in a crawl space with a dirt floor - can that be unhealthy pulling in air from under the house with all the dirt and dust there?

So the galvanized metal box to the left at the other end of the green Rheem furnace with a duct covered with orange insulation is the supply duct that takes warm air up into the house.

There would be no air filter on the supply duct, so the only filter then is the one where the current one is sticking out? So I just need to replace that one filter with the proper size - and I am ok?

I see why you think I may need a custom 21" high filter - looks like there is about an inch gap at the top with the 20" high filter. I think there are some filters that can be custom cut for the size needed.

Thanks for explanations !

 

I saw the register on the return there and it didn't register.....

That register would draw air in from the crawlspace. No that is not a good idea.
Fresh air into the system from outside is a good idea but not from down there.

You pretty much everything down.
It's important for the filter to fit as snug as possible but still be removable.

Common sizes........

• 12 x 12 x 1"
• 14 x 14 x 1"
• 10 X 20 X 1"
• 14 X 20 X 1"
• 16 x 20 x 1"
• 16 X 24 X 1"
• 16 x 25 x 1"
• 18 X 30 X 1"
• 20 x 20 x 1"
• 20 x 25 x 1"
• 20 x 30 x 1"

 

Since there is a return from inside the house and drawing air from a crawlspace is not a good idea, is that return in the galvanized metal box under the house even necessary? Would it be a good idea to block it?

Or if additional air is needed, how would it be supplied as the heater is in the crawl space - would it need another duct connected to the outside of the house - that could be complicated as the opening would need to be protected against the weather - no snow here but rain, smoke, debris, etc.

 

Yes... you should cover that register over.
If you have an older home with lots of air leakage... you don't need to bring fresh air in.