This morning I opened the door that leads from my laundry room into the garage in order to put some recycling into the container. As it was still dark outside, I needed light to see where the recycling can was. I paused for a moment to ponder: is it more efficient to hold open the garage door – thereby utilizing the light from the laundry room, but allowing heat to escape from the house – or to let the garage door close behind me and turn on the garage light, thereby expending extra electricity?

How to measure the heat loss? The cost to replenish those lost BTUs?