They (the IRS) can ask for proof at any time. The IRS also keeps statistical information about the average costs by area, so if something seems out of the ordinary, they may ask for receipts to prove your expenses.
Thanks. But sounds odd though, as cost van vary home to home in the same area significantly due to sizing of the system and also by the company .
So even if we opt for paper filing we dont need to attach any receipt ?
No, Catina is correct that the IRS will determine if they want additional information. The IRS is running up to 4 years behind (depending on the credit in question) so hold on to the receipts for a few years. If they do want more information, you will get a letter.
The IRS will look at your income and the expense along with the other variables mentioned.