In this poem, the narrator remembers his childhood and the way his father would get up early to build the fire that would warm the freezing cold house. The first stanza describes how his father would take on this thankless task of facing the bitter cold and building the fire even though his "cracked hands ... ached." By doing this chore, the father ensured that the son could get up in a toasty home.
At the beginning of the second stanza, the speaker states,
I’d wake and hear the cold splintering, breaking.
The speaker did not actually hear the cold splintering and breaking, as that is not possible. Cold is a sensation, not an object. The speaker is using a metaphor, a comparison without the word like or as, to liken the cold to an object that splinters and breaks.
This metaphor works on several levels. It is effective because, first, something that splinters and breaks is no longer powerful. The cold no longer has any power as the fire's warmth fills the room. Second, because the speaker does not specify what exactly is splintering and breaking in this metaphor, we as readers can apply multiple meanings to it. We can, for example, imagine the kindling that perhaps the father splinters and breaks to throw in the fire as also "splintering and breaking" the cold as it sparks and begins to burn. We could also imagine the cold as icicles that might splinter and break in the warmth before finally melting.
This is a poem about love. By taking on the cold himself so the boy doesn't have to, the father demonstrates his love without having to say the words.