Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2023	Oct. 31, 2023
Document Information [Line Items]
Entity Central Index Key	0000846913
Entity Registrant Name	FUEL TECH, INC.
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2023
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Transition Report	false
Entity File Number	001-33059
Entity Incorporation, State or Country Code	DE
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
City Area Code	630
Local Phone Number	845-4500
Title of 12(b) Security	Common Stock
Trading Symbol	FTEK
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		30,385,297