Note 13 - Segment and Related Information - Information by Industry Segment (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Sales	$ 37,636,088	$ 36,933,015	$ 76,075,727	$ 76,417,371
Gross profit	10,411,315	10,474,878	20,656,348	20,991,429
Operating profit	5,116,181	5,152,364	9,690,271	10,271,632
Interest charges	304,057	366,101	541,898	735,904
Loss (Gain) on investments in equity securities	261,389	(177,515)	379,466	(118,482)
Other (income) expense, net	(5,557)	(345,968)	66,706	(344,971)
Income before Provision for Income Taxes	4,556,292	5,309,746	8,702,201	9,999,181
Operating Segments [Member]
Sales	37,636,088	36,933,015	76,075,727	76,417,371
Gross profit	10,411,315	10,474,878	20,656,348	20,991,429
Operating profit	6,264,328	6,593,302	12,388,243	13,199,599
Corporate and Reconciling Items [Member]
Operating profit	1,148,147	1,440,938	2,697,972	2,927,967
Commercial Air Handling [Member] | Operating Segments [Member]
Sales	16,431,398	14,860,001	33,409,842	30,911,194
Gross profit	5,701,513	5,029,777	11,333,608	9,469,684
Operating profit	4,672,034	3,987,554	9,220,835	7,402,749
Industrial and Transportation Products [Member] | Operating Segments [Member]
Sales	21,204,690	22,073,014	42,665,885	45,506,177
Gross profit	4,709,802	5,445,101	9,322,740	11,521,745
Operating profit	$ 1,592,294	$ 2,605,748	$ 3,167,408	$ 5,796,850