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Sales, Contract Assets and Contract Liabilities (Details) - USD ($)
 3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Revenue $ 363,000 $ 0  
Cost of goods sold 225,000 0  
Cost of goods sold before warranty adjustment 18,000    
Cost of goods sold - warranty adjustment 51,000    
Residual costs 8,000    
Contract assets 339,000   $ 92,000
Contract liabilities 48,000   $ 94,000
Burner Contract      
Revenue 363,000 $ 0  
Cost of goods sold $ 250,000