It's a song less than 20 years old, I think. A man is headed up to bed, but his wife plans to stay up a bit. Before he goes, he reminds her to put more wood in the stove/fireplace and nags her about how it has to be oak because oak burns slowly and puts out steady, gentle heat.

"Oak," he told her. "Oak," she said.

So he goes up to bed, and she sits in the cooling shadows for a while and then quietly loads the stove with birch.

And the logs burned as sweet and hot as a July afternoon,
And the leaping flames saw nothing more than a young bride on her
honeymoon.

The birch burns quickly down, and as she goes up to bed,

She thought of love, she thought of time;
She called it even trade.

Anybody else been haunted by this song? Wish I could remember the words!