Note 13 - Segment and Related Information - Information by Industry Segment (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Sales	$ 38,439,639	$ 39,484,356
Gross profit	10,245,033	10,516,552
Operating profit	4,574,090	5,119,267
Interest charges	237,841	369,802
Loss on investments in equity securities	118,077	59,033
Other (income) expense, net	72,263	997
Income before Provision for Income Taxes	4,145,909	4,689,435
Operating Segments [Member]
Sales	38,439,639	39,484,356
Gross profit	10,245,033	10,516,552
Operating profit	6,123,915	6,606,297
Corporate and Reconciling Items [Member]
Operating profit	1,549,825	1,487,030
Commercial Air Handling [Member] | Operating Segments [Member]
Sales	16,978,444	16,051,193
Gross profit	5,632,095	4,439,907
Operating profit	4,548,801	3,415,195
Industrial and Transportation Products [Member] | Operating Segments [Member]
Sales	21,461,195	23,433,163
Gross profit	4,612,938	6,076,645
Operating profit	$ 1,575,114	$ 3,191,102