Question

what happens if igniting temp. of household materials is below room temp.

Answer 1

We know that $\textbf{ignition temperature }$ is that temperature which is required to ignite a material.

So, if ignition tempertaure is below the room temperature, then each and every household will catch fire.

Answer 2

If ignition temperature of house hold material is below the room temperature then they will catch fire.
Ignition temperature of an object mean any temperature in which the material or object start burning is called ignition temperature.