| Document And Entity Information | Mar. 11, 2024 |
| Document Information [Line Items] | |
| Entity, Registrant Name | FUEL TECH, INC. |
| Document, Type | 8-K |
| Document, Period End Date | Mar. 11, 2024 |
| Entity, Incorporation, State or Country Code | DE |
| Entity, File Number | 001-33059 |
| Entity, Tax Identification Number | 20-5657551 |
| Entity, Address, Address Line One | 27601 Bella Vista Parkway |
| Entity, Address, City or Town | Warrenville |
| Entity, Address, State or Province | IL |
| Entity, Address, Postal Zip Code | 60555-1617 |
| City Area Code | 630 |
| Local Phone Number | 845-4500 |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | FTEK |
| Security Exchange Name | NASDAQ |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity, Emerging Growth Company | false |
| Amendment Flag | false |
| Entity, Central Index Key | 0000846913 |
