Bottom furnace filter (Rheem Mod)

[ampulman]

Looking at the installation manual, it shows 'side' and 'bottom' position for the filter.

Based on information seen on the internet, the side mount is straight forward. Trying to figure out how the bottom mount works, as there only appears to be a minimal amount of clearance between the upstream side of the filter and the bottom. How is the return airflow directed into the filter? Also, I believe I read where the bottom panel of the furnace should be removed. Couldn't this set up the possibility that air (basement) could be sucked into the return path?

Would prefer to have a side mount but bottom offers use of a larger filter. Can contractors fabricate a side mount filter cabinet that can utilize a larger filter?

AM

[WANDERSON41]

How is the return airflow directed into the filter?

I assume that your existing return is going into the side of your existing furnace. In order to get air to come through the bottom of the furnace you will need a plenum underneath it.


Also, I believe I read where the bottom panel of the furnace should be removed. Couldn't this set up the possibility that air (basement) could be sucked into the return path?


You only need to remove the bottom panel if you put the plenum under the furnace.

[ampulman]

I assume that your existing return is going into the side of your existing furnace. In order to get air to come through the bottom of the furnace you will need a plenum underneath it.

You only need to remove the bottom panel if you put the plenum under the furnace.

O.K., it makes sense. Why would anyone opt for this configuration in an upflow furnace? You would only gain 100 sq. in. of filter surface (16 x 25 vs. 20 x 25). Does the bottom plenum have a slot for the filter, or do you have to remove the blower panel to access it?

AM

[WANDERSON41]

Why would anyone opt for this configuration in an upflow furnace?

One reason would be to keep the furnace off the floor.
Another reason is that a 90,000+ BTU furnace needs more return air. If you have a 90,000 + furnace that does not have a plenum under it, then you have to pull air from both sides of the furnace.




Does the bottom plenum have a slot for the filter, or do you have to remove the blower panel to access it?



There should be a filter rack built into it. So yes you would remove the blower panel.

[ampulman]

One reason would be to keep the furnace off the floor.
Another reason is that a 90,000+ BTU furnace needs more return air. If you have a 90,000 + furnace that does not have a plenum under it, then you have to pull air from both sides of the furnace.

There should be a filter rack built into it. So yes you would remove the blower panel.

Although I didn't mention, it is in reference to the '090' modulating furnace. Why would a manufacturer purposely undersize the return cabinet? I seem to recall reading that the 'cabinet' had to be mounted on the opposite side as the gas/electrical connections.

When you talk about 90,000+ furnaces, are you speaking in general or specifically with respect to the Mods? My current furnace is 125,000 BTU (oversized) w/4 ton a/c and has run without problems going on 20 years, with a 16 x 25 (not ideal) filter.

AM

[WANDERSON41]

I don't know why they would undersize the cabinet.
The plenum is sometimes mounted opposite of the electrical/gas to avoid mounting the plenum too close as to interfere with install or removal of electrical/gas. But if you install a full sized plenum on the opposite side and an almost full sized plenum on the gas/electric side you should be ok.( You are just looking to get more airflow.)



My current furnace is 125,000 BTU (oversized) w/4 ton a/c and has run without problems going on 20 years, with a 16 x 25 (not ideal) filter.



Could be just a quirk, who knows. Maybe you just held your tounge just right all these years. lol :D

[ampulman]

Could be just a quirk, who knows. Maybe you just held your tounge just right all these years. lol :D

Trying to figure that one out.

AM

[WANDERSON41]

Sometimes a system will work well enough for a long time even when not properly installed. Often I have been out to do an install and while taking out the old unit ,discover that something wasn't quite right and wonder how the unit ran like this for so long.

[ampulman]

Sometimes a system will work well enough for a long time even when not properly installed. Often I have been out to do an install and while taking out the old unit ,discover that something wasn't quite right and wonder how the unit ran like this for so long.


Well, it was new construction. The guy and his crew were real hacks. The furnace caught fire the first time we ran it. He just tucked the burnt wires out of sight (found years later). Don't ask about the ductwork.

I guess I got one of those.

AM

[dash]

Well, it was new construction. The guy and his crew were real hacks. The furnace caught fire the first time we ran it. He just tucked the burnt wires out of sight (found years later). Don't ask about the ductwork.

I guess I got one of those.

AM

If you do,make sure you find a contractor that can test and remediate any duct system issues.

[ampulman]

If you do,make sure you find a contractor that can test and remediate any duct system issues.

Thanks Dash. Actually, it was a little exageration on the ductwork. Had low flow from one register, opened the damper all the way, but still no flow. Traced the run and found about a 3" gap between the duct and the oval elbow. It seems that they had to break some cinder block to fit the run in place, but didn't go far enough. About 10 minutes with hammer and chisel took care of it. Joined, fastened, and sealed the duct. Now getting good air.

AM

[docholiday]

Here's my take. The mfg's provide a filter and a clip to hold it because they have to and know, especially on premium products that a better filter arangement will be used. I can't imagine installing a mod furnace without a proper filter rack installed outside the furnace. Either an EAC, SpaceGaurd, Filter Grill or at the very least an exterior filter slot. The homeowner should not be pulling the blower door to change filters, especially on one with as much going on down there. IMHO, it's a substandard installation practice that makes regular maintenence by the HO difficult and when it's difficult, they will ignore it.

Dont blame the furnace. Anyone can unbox a furnace and tape some ductwork to it, longevity, reliability, performace, and a bunch of other things are jeoprdized when things are hacked in.

[ampulman]

Here's my take. The mfg's provide a filter and a clip to hold it because they have to and know, especially on premium products that a better filter arangement will be used. I can't imagine installing a mod furnace without a proper filter rack installed outside the furnace. Either an EAC, SpaceGaurd, Filter Grill or at the very least an exterior filter slot. The homeowner should not be pulling the blower door to change filters, especially on one with as much going on down there. IMHO, it's a substandard installation practice that makes regular maintenence by the HO difficult and when it's difficult, they will ignore it.

Dont blame the furnace. Anyone can unbox a furnace and tape some ductwork to it, longevity, reliability, performace, and a bunch of other things are jeoprdized when things are hacked in.

Good advice, Doc. Still working up quotes. Spoke today to one of my contractors--will likely go deluxe filter route. BTW, have been pulling the blower door for the last 20 years.

AM

[docholiday]

The previous 20 years required you stick your hand in a handle and pull up. The mod 90 has thumb screws that will ultimately be too tight to turn after you open and close it enough. The internal filter rack if on the bottom will require you to bend the filter slightly to get a cardboard framed filter in and still be wide enough to cover the opening. For side filters, they will have to make sure to place the internal condensate trap and electrical connections on the opposite side of the filter so you can get one in and out. It's just substandard, but I guess that's all subjective.

Good choice on the furnace though.