Built a new room and it stays hot. HELP

[linalli]

A few short months ago we purchased a new house. The previous owner had built an addition onto the house. He made it one long room the width of the house with 2 heating/ac vents (one on each end of the room). We decided to divide the room into two. Making one side a small bedroom and the other side a small den. We only have one side of the dry wall up at this time. We haven't put the drywall on the inside of the bedroom yet. The den side has a set of French doors leading to the deck and also the back door of the house leading to the steps and a window. The bedroom side has 2 windows. All windows and doors are the new, insulated kind. The exterior walls are also insulated. All we did was install a wall and an interior door. We didn't have to touch the heat/ac or wiring (except to install a light switch). The windows do have blinds and curtains.

When we built the wall and added the door the new bedroom stays very warm. Even with the door cracked open for ventilation at night (we're still working on the room so the wall airflow vents haven't been installed yet) the room stays very warm but the other room is cool. Even with the door completely open that side stays warm. We put thermometers in each room and there is at least an 8 degree difference on really hot days. The air coming out of the ac vent is blowing just as strongly as it is on the other side of the wall and just as strongly as it did before the wall was built.

The rest of the house is fine. Heats well and cools well. Its only that new bedroom where we are having issues.

What could be the cause and how do I fix it? Do we need to install a 2nd heat/ac vent?

I'm sorry I don't know the brand/model of my heat pump/ac unit right off the top of my head as I type this.

[Brian_UK]

Have you checked the air temperatures coming out of the vents?

Are the vents both supply air? Not one supply and one return air.

[frank]

It sounds like you have built the new partition in the middle of the airflow.

The cool room may have all of the incoming air so cools the room nicely and then the hot room has 2 issues. 1 - lack of airflow 2 - Any airflow is heated by the previous room

I would hold a piece of tissue paper up at each grille as a first step to determine if the air is flowing in to or out of the room

[linalli]

Yes, we've checked the air flow from the vents. The flow is INTO each room. Not out.

[Brian_UK]

There needs to be a return air path for each side of the room. I understand that you tried with the bedroom door cracked open.

Has the airflow rates from the vents been balanced to ensure that the correct airflow rate for each room is available?

[linalli]

We do plan to put the vents into the walls for airflow. Just haven't gotten that far yet on the room.

As for the airflow rates...I don't know how to balance them. How do I do that?




There needs to be a return air path for each side of the room. I understand that you tried with the bedroom door cracked open.

Has the airflow rates from the vents been balanced to ensure that the correct airflow rate for each room is available?

[Brian_UK]

To measure the airflow rate through the grille you will need an anemometer.

This instrument will measure the velocity of the air, you then measure the size of the grille, height x width, to find the grille area in square feet. Multiply the velocity, in feet per minute (from), by the area to get the airflow in CFM or cubic feet per minute.

Use your favorite search engine to find a cheapish anemometer, a proper one will be expensive so the choice is yours.
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Once you have the CFM you can then calculate the room air change rate.
Here is a description of this and a handy calculator....

https://learnmetrics.com/air-changes-per-hour-calculator-and-formula/