Furnace filter size

20x30x1 Furnace Filters

The tightest gap between printed size and stated measurement anywhere in this catalog.

Depth — 0.81 in stated on both listings, against a nominal 1 in

Twenty by thirty is a larger return slot, and the two filters here get closer to their printed name than anything else in this catalog — within 0.12 in on both faces. That is the exception, not the rule, and it does not generalize to other manufacturers at this size.

A closer fit is not automatically better. A frame built almost to nominal will bind in a slot that was cut generously, and forcing a cardboard frame into a rail is how a filter ends up creased and passing air around its own edge.

This size is stocked here at MERV 5 and MERV 8, the two lowest ratings in the catalog. Both listings also state an MPR figure — 300 and 700 respectively — which is a different scale from MERV and does not convert into it.

What this catalog carries at 20x30x1

2 filters, at MERV 5 and MERV 8.

Stated figures at 20x30x1

Listing	Actual size stated	MERV	MPR	Pack
Filtrete 20x30x1 MERV 8, 4-pack	19.88 x 29.88 x 0.81 in	MERV 8	MPR 700	4 per box
Filtrete 20x30x1 MERV 5, 6-pack	19.81 x 29.81 x 0.81 in	MERV 5	MPR 300	6 per box

Filtrete 20x30x1 MERV 8, 4-pack
Actual size stated
19.88 x 29.88 x 0.81 in
MERV
MERV 8
MPR
MPR 700
Pack
4 per box
Filtrete 20x30x1 MERV 5, 6-pack
Actual size stated
19.81 x 29.81 x 0.81 in
MERV
MERV 5
MPR
MPR 300
Pack
6 per box

Check the one you have first

Read the nominal size on the frame of the filter that is in the slot now.
Measure all three dimensions on the frame, and measure the slot opening too if the old filter was ever hard to get in.
Note the arrow direction before the old filter leaves.
Compare against the stated actual size in the listing — at this size the numbers are close to nominal, which makes slot clearance the thing to check rather than the filter.

The arrow, and the schedule

A 30-inch filter is awkward enough to handle that it tends to go in whichever way it fits through the opening. Slow down for one second and find the arrow: it points toward the blower, and a filter this size loaded from the wrong face collapses sooner than a small one would.

Follow the filter manufacturer interval and the system documentation. A 30-inch face carries more media than the smaller sizes here, which helps at equal running hours, but it does not change the schedule the manufacturer publishes.

A higher MERV rating is not an upgrade by default

MERV 5 and MERV 8 are both in the lower resistance band, which is where the least restrictive option in this catalog sits. That is still not a reason to move up or down without checking. The system manufacturer documentation states the rating and pressure drop the equipment is designed for, and a licensed HVAC professional can advise where the document is unavailable. A clean filter at a moderate rating restricts airflow less than a loaded one at a fine rating.

The 20x30x1 filters in this catalog

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Filtrete 20x30x1 MERV 8, 4-pack

Nominal 20x30x1
Actual 19.88 x 29.88 x 0.81 in
MERV 8
MPR 700
4 per box

A 20x30x1 filter with a stated actual size of 19.88 x 29.88 x 0.81 in, which is the closest any listing in this catalog comes to its nominal number. MERV 8 with a stated MPR 700. Compared with the MERV 5 filter in the same nominal size, the frame here is stated a fraction larger on both faces.

What the listing supports, and what it does not

Stated actual size sits within 0.12 in of nominal on both faces, the tightest gap here
MERV 8 with MPR 700 stated, so both scales are on the label
Four per box covers a year at a quarterly schedule
The larger 30-inch face gives more media area than the 25-inch sizes
A frame this close to nominal can bind in a slot that was cut generously
MERV 8 is a step above MERV 5 in resistance as well as in rating
20x30x1 is less commonly stocked than 20x25x1 if a replacement is needed urgently

Best forA 20x30x1 return where the frame has previously been too loose.

Check it on Amazon

Filtrete 20x30x1 MERV 5, 6-pack

Nominal 20x30x1
Actual 19.81 x 29.81 x 0.81 in
MERV 5
MPR 300
6 per box

The lowest MERV rating in this catalog at MERV 5, with a stated MPR 300 and an actual size of 19.81 x 29.81 x 0.81 in. Low rating is not a defect — it is the least restrictive media stocked here, and a clean MERV 5 does more for a system than a loaded MERV 12. Six per box, pleated electrostatic per the listing.

What the listing supports, and what it does not

The least restrictive media in this catalog by stated rating
Actual dimensions are stated to hundredths on all three axes
Six per box, the largest quantity in this nominal size
Pleated electrostatic construction is stated rather than a flat panel
MERV 5 captures a coarser range than the MERV 11 and 12 options here
MPR 300 is the lowest figure on that scale in this catalog
20x30x1 is a less common slot size to restock in a hurry

Best forA 20x30x1 return where keeping resistance low is the priority the system documentation points to.