| Document and Entity Information | Dec. 17, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | GENCOR INDUSTRIES INC |
| Amendment Flag | false |
| Entity Central Index Key | 0000064472 |
| Document Type | 8-K |
| Document Period End Date | Dec. 17, 2021 |
| Entity Address, Address Line One | 5201 North Orange Blossom Trail |
| Entity Address, City or Town | Orlando |
| Entity Address, State or Province | FL |
| Entity Address, Postal Zip Code | 32810 |
| City Area Code | (407) |
| Local Phone Number | 290-6000 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-11703 |
| Entity Tax Identification Number | 59-0933147 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock ($.10 Par Value) |
| Trading Symbol | GENC |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
