The heat within the core of the natural reactor builds.

The heat was building outside, and it was best to get things done quickly.

It was only 10 a.m., but we were running low on water and the heat was building.

The heat was building, the grass was drier than it had been just two weeks ago.

If it shut down those systems, the heat would build up and destroy Trantor.

Yet already the heat was building, radiating up from the parched ground.

The day's shimmering heat built towers of black clouds in the sky.

The heat builds just as it did outside on the shale ledge so far away.

The day's heat built; usually they were home by this time.

The heat built up there, failing the hydraulic lines.