Ok, this takes place during the winter. The house has central heating. The thermostat is located in Room A, at the far end of the house. Room B is located around the middle of the house on the same floor.
Room B, with the door closed, gets unusually hot compared to the rest of the house. Let’s say about 80-82 degrees Fahrenheit. Cracking the window open brings the temperature of Room B down to about 76-74.
My question is: given that the door to Room B is closed and that cracking the window open has only cooled down Room B a bit, does cracking the window open affect the thermostat in such a way that it makes the heating system work harder?
The answer is yes. Somewhere in room B there is a cold-air return duct that brings room air back to the furnace whenever the blower is operating. With the window open, it’s bringing 75-degree air back to the furnace instead of 81-degree air. When the furnace is running, the hot air being distributed to the whole house will be somewhat cooler because of this, and the furnace will have to run longer to heat the house up to the desired temperature.
Clarification: it’s not affecting the thermostat at all. It’s just wasting energy, and the furnace has to make up the difference.
if room b is hotter than the rest of the house then it slowly and to a small amount adds heat to the rest of the house and to room a. so room b being warmer might cause the heating system to come on so amount (maybe very small) less.
thermostats work better in the interior rather than an end of the home.
if possible occasionally open the door to room b and have a box fan blow that warmer air into the rest of the house rather than waste it.
one of the advantages of a forced hot air system is how easy it is to deal with this - don’t open a window, partially or full close (they make magnetic seals for this purpose) some or all of the vents in rooms that are warmer while fully opening the vents in rooms that are colder until your system is balanced.
Most forced air systems I’m familiar with do not have an intake in every room. That is usually located in a hallway or a common area close to the FAU.
If Room B is the closest to the furnace, it’s gonna get the heat directly from Hell, and it will be an unbalanced arrangement. I vote to close the vent in Room B partially and see how that helps. If it’s still too warm, just close it all the way. Vents are notoriously difficult (especially when gummed up with paint) to adjust, and it may be difficult to find the perfect setting.
~VOW
I dealt with a similar problem by installing a wireless thermostat in place of the old one. In our case, it was insufficient cooling in the kitchen that was the problem (we have a split-level house, and the thermostat was downstairs , which meant the upstairs would get very hot before the AC came on). By putting the remote sensor in the kitchen, that room stays comfortable, and the rest of the house has less of a temperature swing.
Thanks, but I am not looking for solutions, just the answer to my question in physical terms.
I don’t understand how the cold air could cool the rest of the house if it can barely put a dent in the temperature of the closed room, given that there is no return duct.
It’s not the cold air from your open window cooling off the rest of the house.
It’s all the warm air that you PAID to heat streaming out the window into infinity. The same concept as shredding twenty-dollar bills and flushing them down the toilet.
~VOW
You are correct that the system isn’t directly working harder.
Indirectly, however, it is.
The house is unbalanced from an air flow perspective. By allocating the heat where it is needed (and where you don’t have to open a window…) the system will work less.
if room b is hotter then the rest of the house then some heat goes from that room to the rest of the house. if room b is hotter than the thermostat setting then any heat from room b will cause your heating system to run less.
opening the window is throwing money/heat away. opening the door to room b more rapidly shares that existing heat with the rest of the home, keeping the door to room b closed and the windows in room b closed more slowly shares that heat with the house.
With the window closed you are putting more hot air in room B than necessary to keep it worm. When you open the window in room B you now have hot air being blown into room and out the window.
Yes your system will have to run longer to heat the rest of the house. Your system can put out so many BTU’s of heat per hour. With the window open a part of those BTU’s are going out the window leaving a smaller amout to heat the rest of the house.