Do you have rooms that are always cold even when the rest of the house is warm? This can be a common complaint with forced air heating systems. Here are a few simple things you can to improve the temperature. This applies to electric, gas or oil force air heating systems used for residential and small commercial applications.
Lets start with the furnace fan running at high speed. Some thermostats will allow you to select |Low Med & High fan speeds while most just have a switch at the thermostat. On/Auto. The On mode should start the fan and Auto will run the fan with the heating or cooling call.
Look around the room and locate any vent openings. Supply air vents are normally located above or below a window. There may be more then one supply vent in the room if its more than 100 square feet. You want to make air is flowing from the vent. If there is little or no air, check for a damper in the vent. This could be a sliding lever or wheel or even a recessed screw that opens and closes the damper. If you can see a damper at the outlet , there should be a way to adjust it. These recessed screws can be hard to see.
Return air vents should be on the interior area , away from the windows. They can be on the ceiling, walls or floors. A clever interior designer can also hide them in the architecture of the room. Some rooms may not have a return grill but rely on the gap under the door. Under cutting the door to the room 3/4″ is a common method to return air to the furnace if there is no return vent in the room. Add a carpet to a floor can choke these gaps off. Return vent can also get blocked by furniture and other decor.
Return air vents get dirty over time which can start to block the air flow if the vent is hidden somewhere, it will never get cleaned. Simple vacuum over the face of the grill once in while keeps them grill clean. If you have grill that never seams to gets dirty, likely means no return air flow and only looks like a return grill.
If you can’t the feel air flow with your hand on the return grill, try using a lighter. Air velocities on return grills can be very low. There should be enough of a draft but to bend the flame towards the grill when the fan is running.
With the fan running, check the air coming out of the vent. Can you feel air blowing on your hand? The amount of air should be enough to feel air flow if the grill is correctly sized. Enough to blow out a candle if held near vent at least.
You can compare the air flow to other rooms that do not have issue and similar vents. How does it compare it to the cold room? If its the same then that is a good indicator the air flow may not be the issue. If air flow is less or much less could indicate the problem as low air flow.
Check the air flow again with all the doors and windows closed. Does the air flow drop off when the door is closed? If the room is pressurizing, it will reduce the air flow and can even it stop it completely. Does the room get cold only when you close door?
There is not enough air flow, now what?
There must be something else