Were do I put a Rebate check I recived for installing a New Heating unite.

According to the IRS  "A cash rebate you receive from a dealer or manufacturer of an item you buy isn't income, but you must reduce your basis by the amount of the rebate."

 

"Example 36. You buy a new car for $24,000 cash and receive a $2,000 rebate check from the manufacturer. The $2,000 isn't income to you. Your basis in the car is $22,000. This is the basis on which you figure gain or loss if you sell the car, and figure depreciation if you use it for business."

 

IRS Pub. 525 Taxable and Nontaxable Income (page 32)

 

 

Note that because it is treated as a reduction in cost it is also a reduction of any credit you could have claimed.  For example, if you installed an efficient furnace for $3000, and received a rebate of $500 from the utility, then the cost you should use to calculate any energy credits is the reduced cost of $2500.