So if I add window units, I could deduct them, since they are removable?
In fact, you have the choice to deduct them, or depreciate them over 5 years as an appliance, provided the cost is less than $2,500. If you deduct them and later sell the property leaving them installed, then you must show a sale price for the window units separately and 100% of that sale price is taxable income to you.
Otherwise, if you depreciate them as an appliance over 5 years and sell the property with the window units still installed, you are required to recapture that depreciation in the year of the sale. I myself would chose to depreciate them over 5 years. Then when that window unit breaks and needs to be replaced I will report the disposition of the non-working window unit as "end of life" and leave it at that so that I don't have to recapture the depreciation when I sell the property.
