Gas and Oil Home Heating Furnaces - Correct size filter for Lennox Merit G40UH-36B-X

I purchased my home new about 4 years ago, and the builders installed a Lennox Merit G40 UH-36B furnace in the house. It is installed on the 2nd floor, in a laundry room along with a gas water heater, and electric dryer.

They had put in a 16x25x1 furnace filter in the unit at that time. Every time that I have replaced the filter, I've just kept it at the same size. However I have always noticed that it doesn't seem to fit properly. Looking on the Lennox website I can't seem to find out verification of what the correct size of the filter should be.

The thing that I feel is the problem is that the filter doesn't lie flat. It rests beneath the burners, and there is a metal lip there. The 16x25x1 filter seems to be about a 1/4" too long, and actually sits on top of this lip, keeping the filter at a slope that allows air to travel around it without going through the filter.

I'm pretty much a novice when it comes to furnaces, but it seems that the filter should lie flush and flat.

I'm also confused by something that I read in the 'use and care manual' from Lennox website:

"This unit is not equipped with a filter or rack. A field-provided high-velocity filter is required for the unit to operate properly. A filter must be in place whenever the unit is operating."

Does the 'not equipped with a filter or rack' indicate that where I'm placing the filter isn't really the spot for it?

The laundry room has always been pretty 'gunked up' with lent, dog hair, and the like, and it is now affecting the performance of the gas water heater (which I'm about to post about separately in the water heater forum). I'd love to figure out if I'm doing something wrong.

Use and Care manual: http://www.lennox.com/pdfs/manuals/Lennox%20G40UH%20Manual.pdf

Produce Brochure:
http://www.lennox.com/pdfs/brochures/Lennox%20G40%20Gas%20Furnace.pdf

Is the filter inside the blower housing in the lower part with the return going in from the bottom or side?

Are you able to post a picture for us to see your set up?

As for lint issue, make sure the exhaust pipe behind the dryer is hooked up, and sealed with foil tape.. (NOT duct tape)

Is the filter inside the blower housing in the lower part with the return going in from the bottom or side?

Are you able to post a picture for us to see your set up?

As for lint issue, make sure the exhaust pipe behind the dryer is hooked up, and sealed with foil tape.. (NOT duct tape)

Yes, the filter is inside of the blower house in the lower part directly below the blower motor itself.

I threw together a quick series of photos of what I'm trying to describe.

The page of pics is here:
http://www.duane-o.com/temp/furnace.cfm

- The first is just the lennox diagram of the unit.
- The following 3 are of the area where I am placing the filter, you can see the metal lip that I feel the filter should go behind and be flush with
- the last 4 are with the actual filter in place, you'll see that it is on top of the metal lip, and the last pic tries to show the slope and gap where air can get around the filter. I know it's not a big gap, but I'm just trying to figure out how to eliminate the amount of dust/lint in the air.

I took note of your comment about the exhaust pipe on the dryer, and I didn't take a look this morning when I was shooting these pics, but I'll have a look tonight.

Thanks for any comments
Duane-O

Duane,

Thanks for sharing the pictures... As they say, "Pictures are worth a 1,000 words."

I see that lip you are talking about.. I went and looked at the install manual

http://www.hvac-direct.com/Installation_instructions.htm

Page 12, Table 1, shows your size you got now.

In the back, is there a channel that the filter slips into? (some I've seen spring loaded) Otherwise, what is holding the filter down into it's place when the blower is sucking air in?

If air filtration is not a big issue, you can use those "hog hair" air filter and cut down to size, to fit in snug on all 4 sides. Home Depot has this filter.. It's blue and kinda like a plastic fiberglass that you just cut down and wash monthly.

No, there doesn't really appear to be a channel in the back, it just goes straight back to the back wall of the unit.

I never really thought about what happened to the old filter when the blower was running, since it doesn't run with the door off I'd never seen it. But I guess with it resting on the lip lick it was, it would just blow up with the air until it hit the blower motor itself.

While I was out at the hardware store today, I went ahead and picked up a new filter of the 16x25x1 size, and I did my best to get it to fit. It took about 30 seconds of forcing it into the unit, and I guess it does lie in there, although it is scrunched up and bent near the front. I suppose that won't make any difference, but it just seems that my old units provided a much better fit than this unit does.

I've put up some pics of how the new filter looks after I squeezed it into the spot.

same webpage, just added them to the bottom.

http://www.duane-o.com/temp/furnace.cfm

Am I correct in assuming that it's ok to have the filter crammed in like that?


Duane-O

Duane,

Yeah, that will work just fine. That style of filter, just change it more often, cuz it will load up much faster.

Did you have a chance to check behind your dryer for the vent hook up?