Lennox ML180UH045E36A furnace filter size
This furnace takes a 16 x 25 x 1 filter (side return) or a 14 x 25 x 1 filter (bottom return), depending on where the return air comes in.
Every filter option for this model
| Where return air enters | Filter size (inches) | How many |
|---|---|---|
| side | 16 x 25 x 1 | 1 |
| bottom | 14 x 25 x 1 | 1 |
Where the filter goes
external, field-provided (side or bottom return); doc: "This unit is not equipped with a filter or rack. A field-provided high-velocity filter is required for the unit to operate properly."
The maker does not ship a filter with this furnace. The size above is the maker's recommended size at the furnace; if your home has a filter grille in a wall or ceiling, that grille sets the size instead.
How often to change it
General guidance, not from the maker's table: 1-inch filters every 1 to 3 months; 4- and 5-inch filters every 6 to 12 months. Change sooner with pets, smoking or construction dust.
About this model
| Cabinet width | 14.5 in. |
|---|---|
| Airflow direction | upflow/horizontal |
| Heat input | 44,000 BTU/hr |
| Efficiency (AFUE) | 80% |
| Model number note | Lennox adds -01/-02 etc. revision suffixes on nameplate; K = R-454B refrigerant-detection version |
How to read a Lennox model number
Source
- ML180UHE Installation Instructions 507103-04 (04/2024) (installation manual, page 11): document. Read 2026-11-03.
- ML180UHE(X) Unit Information Corp 1120-L4 (04-2024) (service manual, page 28): document. Read 2026-11-03.
Check that the model number on your furnace label matches, and compare with the size printed on your old filter. If they differ, go by the filter that fits your rack.