I opened the guest-room door with clean sheets under my arm and immediately went back for socks. My mother was arriving that evening. I had closed the room's heating register a fortnight earlier because nobody was using it.
The decision had felt tidy: one less room to heat. Now I was turning the thermostat up in the hallway while carrying blankets upstairs. The hallway, which had never complained about being cold, received most of my attention.
A register is part of a larger air path
Closing registers changes airflow through a forced-air system. Carrier warns that too many closed vents can contribute to poor heating and short cycling. A system is not automatically designed to send the same useful heat elsewhere whenever a room is shut off.
I reopened the register and checked that the bed skirt was clear of it. I left the other registers in their normal positions. The room needed time, and there was no reason to treat a higher thermostat setting as a fast-forward button.
If a room is habitually unused, a designed zoning solution may be worth discussing. That means assessing equipment and ductwork together. It is a different job from closing whichever grille happens to be within reach.
The question for a cold room
I wrote down when the room was cold, whether its door was open, and how it compared with the adjacent bedroom. Those observations would help distinguish an airflow issue from heat loss through the room's walls or windows.
By bedtime the guest room was more comfortable, though I still put an extra blanket at the foot of the bed. My mother folded it neatly and left it there. I stopped using her room as an unmeasured energy-saving experiment and put the vent lever back where it belonged.
