Hello!

I'm surprised fire ants made it into your home. When it gets hot, they usually go deeper in the ground. Are you sure they are fire ants and not tawny crazy ants?

Going with fire ants, we recommend the two-step method which involves bait and then individual treatment. 

Ant bait is highly effective. It's best used when temperatures are a little cooler (spring and fall.... right now). Do not over-apply bait. Very little is actually needed to be effective so read the label carefully. With bait, there are ants whose job is solely to go out and collect food to bring back to the queen and workers. Those first ants do not eat. The bait is then ingested by the queen, killing her.  

Powders sprinkled on top of a mound, simply affects a few ants on the surface. Then the ants below the ground are signaled to move. This doesn't solve the problem. 

Red Imported Fire Ants - Harris (agrilife.org)

Spring is the time for Texans to ‘two-step’ toward fire ant control - AgriLife Today (tamu.edu)

Best of luck!