Tax question on Water Heater replacement

[Chris Masons]

I have a tax question on water heater replacement. I Know it should be a capitalized expense written off over X amount of years. Last year I replaced a water heater and in doing my taxes using Turbo Tax there was something that said I have the one time option of writing off the entire expense in that tax year. I said yes to the option and the entire cost was written off.

I just replaced another water heater in another property and was wondering if I will have that option again or mainly I want to know whty I Was given the option to deduct this fully in the given tax year as opposed to it being a capitalized expense and written off over I believe 7 years is it?

thx in advance,
Chris