[header] How to block off a heating vent [title] Measure the height and length of the vent. [step] To measure the height of the vent, measure from the bottom edge to the top edge. To measure the length, measure from the left edge of the vent to the right edge. 
[substeps] Write down the measurements you take so you don't forget them. [title] Buy a sheet magnet that's at least as big as the vent.