Is a home sale capital gain within the federal exclusion limit of $250,000 considered income when applying for subsidy? i.e. if I sell my home in 2016 and the net capital gain is under $250,000, will i be required to repay any subsidies grated to me for 2016 when I file in 2017?
Capital gains from the sale of your primary home under $250,000 can be excluded and don't affect subsidies. The exclusion is $500,000 for a family.
Since the money is excluded from your taxable income, it doesn't get added in to household income (which subsidies are based on). The rest of the money is taxed at 3.8% and counts toward subsidy income (that tax, a Medicare tax, was created by the ACA and applies only to dollars over the exclusion amount; it is owed to the federal government for the year you sell the property along with the standard capital gains tax on dollars over the exclusion amount).
Capital gains (in respect to the sale of a primary home) = the profit you made from your house, not the total amount of money you get from your home.
Please note that other capital gains (such as from stocks) generally count toward income (unless another exclusion applies).
The above is only true if you qualify for the exclusion. See this page for more details, see IRS for official information.