Why Is My Upstairs Bonus Room So Hot? (6 Causes & Fixes)

If you have a bonus room in your home, you probably love to use it for a variety of purposes. Some people decide to turn their bonus room into a home theater, while others might use it as a game room for the kids. You might even turn your bonus room into a home gym, or you might have a pool table up there. Regardless, this is probably a spot you like to use to entertain yourself, your family members, and your friends.

As a result, it can be really frustrating when your bonus room feels more like a sauna than, well, a bonus room. What do you need to do to fix the issue? The first thing you need to do is figure out why your bonus room has gotten so hot. Then, you can fix the issues.

Why Is Your Bonus Room So Hot?

A treadmill and handheld gym equipment on a room with some mirrors on the far wall
A bonus room currently used as a makeshift gym

There are a few potential reasons why your bonus room is so hot. Some of the most common reasons include:

1. The HVAC System Is Not Working As It Should

Now, this is an issue to consider if you feel like the entire house is hot. If the entire house is hotter than it should be, you need to turn your attention to the HVAC system. The HVAC system might need to have its filters replaced, there could be an issue with the condenser, or the thermostat might not be working correctly.

What this means is that you might not have the thermostat on the settings you think it is set to, or you might not have a thermostat that is responding appropriately. If the entire house is hot, turn your attention to the HVAC system first. On the other hand, if it is only the bonus room that is not working properly, read on.

2. The Bonus Room Is Directly Above the Garage

This is another very common reason why your bonus room might feel a bit hot. If the bonus room is right above the garage, it does not have the best source of insulation. The garage is typically not insulated, which is why the garage always feels like it is at a very different temperature from the rest of the house.

What he means is that the bad insulation in the garage transfers heat directly to the bonus room, causing it to feel like a sauna. This could be the reason why your bonus room is so hot.

3. There Are Knee Walls Around the Attic

If your bonus room is very close to the attic (such as right next to it or directly below it), your bonus room might have knee walls around the attic space. These knee walls feature fiberglass insulation in and around the framing, which means that hot air can move around the fiberglass, causing the walls themselves to heat up.

When the walls heat up, the room heats up as well. The heat radiates into the room, making your bonus room feel like a sauna. As you use your bonus room more often, some of these knee walls can develop issues, causing the room to heat up even more.

4. Poor Air Circulation In the Room

Diagram showing air circulating out of an AC unit
Diagram showing air circulating out of an AC unit

Because of the position and shape of the bonus room, the air might not circulate as well. The door to the bonus room might remain closed a lot, and if the air is not able to escape through any windows, it could get stuck.

When the air stops circulating, the room starts to feel warm and musty. This could even lead to potential mold and mildew issues. If you feel like your bonus room is a bit sticky, there could be a circulation issue.

5. The Ductwork Is Not Appropriate for the Room

If you have central AC, you probably have ductwork that feeds the bonus room to keep it cool; however, if you look up and only see one vent, it is possible that it might not be big enough to cool the room appropriately.

That one duct might be appropriate for a bedroom, but if your bonus room is two or three times the size of the bedroom, this is not enough circulation. You need to improve the ductwork feeding the bonus room if you want to keep it cool.

6. The Windows Are Not Energy-Efficient

If you have windows to your bonus room, think about how much sun they get during the course of the day. Unlike the windows on the first floor, there is a good chance that the windows to the bonus room do not have any plants in front of them to block the sunlight.

As a result, the sunlight just builds and builds in the room, particularly if the door is closed. If you are hit by a heatwave when you open the door, there is a chance that this is the culprit. You need to address this issue if you want to cool down the bonus room.

These are just a few of the many potential reasons why your bonus room might be hotter than it should be. Take a look at a few ways you might be able to improve the temperature of your bonus room and make it more comfortable.

How Do You Fix The Issue?

If you want to improve the temperature control of your bonus room, there are a few potential ways you can fix the issue. They include:

1. Install a Ceiling Fan

An old style ceiling fan
An old style ceiling fan

This is one of the most straightforward ways to cool down your bonus room. A ceiling fan is helpful because you can use it to increase the air circulation throughout the room, which will immediately have a powerful cooling impact.

In addition, you don’t have to worry about messing with the thermostat and throwing off the temperature of the other rooms in the house. By improving the circulation, you can prevent the air from getting musty, which will make the room feel cooler.

Best of all, this is a relatively inexpensive fix. There is a good chance that there is a ceiling fan hookup on the ceiling already. If you can install it yourself, this shouldn’t cost you any more than a few dollars.

2. Plan Some Tall Trees (or Install a Blackout Shade)

If you are looking for a way to deal with continuous sunlight coming in through the room, you have a few options available. You might want to plant a few trees in front of the window to block the sunlight. That way, you don’t have to worry about your bonus room feeling like the inside of a car.

If you are looking for a non-permanent option, you might want to install a blackout shade. Keep in mind that you might be looking for a way to warm up the room in the winter. A blackout shade can be pulled down and pulled up at will (if you get the right one).

3. Open Up the Ductwork a Bit More

If you have ductwork that is too small for the room, you might want to open up the ductwork a bit more. You can start by cleaning the ductwork and replacing the filters to get more air circulation throughout the room. You might notice that this is all it takes to make a major difference.

If that still isn’t enough, you might want to add a second or third return. You might need to reach out to a professional who can help you with this, but if you are handy, you might be able to do it yourself.

4. Replace the Windows

This is another easy fix that you can use to cool down the bonus room. If you do not have energy-efficient windows, you are letting in a lot of sunlight and outside heat. In addition to planting trees, you can install windows that reflect the sunlight instead of letting it in. Then, you can bounce those warm rays right off of your bonus room.

5. Add More Insulation

This is arguably the most direct way to cool down the bonus room. You can add more insulation around the walls of the room and under it (if your bonus room is directly above the garage. This can make a major difference in your ability to keep the bonus room cool.

If you have never done this before, make sure to avoid insulation that could potentially be toxic. Then, ensure you install it properly and safely. Don’t hesitate to ask for a professional to help you.

6. Install a Ductless Mini Split

If you have experience with HVAC systems, you might want to install a ductless mini-split. This is a system that doesn’t require any ductwork, is quieter than a normal window unit, and doesn’t require a window. It also lasts longer than a typical window unit and most people find it more aesthetically appealing. Consider installing a ductless mini-split to help you keep your bonus room cool.

These are just a handful of ways you might be able to cool off your bonus room. Remember that you always need to put safety at the top of your priority list. If you ever feel uncomfortable working on something, you need to reach out to a professional who can help you.

Frequently Asked Questions About Cooling Off a Bonus Room

Someone looking at an air vent in a room
Someone looking at an air vent in a room

There are a few common questions people ask about cooling off the temperature in the bonus room. A few examples include:

Why are bonus rooms frequently built above the garage?

The biggest reason why bonus rooms are often built above the garage is that most of the other rooms on the second floor (or third floor) are bedrooms. The builders do not want to put a bedroom above the garage because if someone opens the garage door in the middle of the night, they will wake up the person sleeping in there.

Does how I use the bonus room impact the temperature of the room?

The purpose of the bonus room should not have a major impact on the temperature, but the one exception to the rule is if you use the bonus room as a home gym. If you turn the bonus room into a home gym, you are going to heat it up quickly. You might need some additional cooling if you want to keep the bonus room cool as a home gym.

How come bonus rooms don’t often come with ceiling fans when they are installed?

There are a few reasons why bonus rooms don’t often come with ceiling fans. One of the reasons is that the builders are looking for a way to save money. Another reason is that the builders don’t know if the owners want to use that ceiling socket for something else. Regardless, you should be able to add one later if you want.

About Charlie D Paige

Charlie is a massive DIY fan, with dozens of DIY projects under his belt - ranging from tiling to electrics, and concrete pads to walls. Charlie loves tinkering, seeing how things works, the outdoors and playing with power tools... so is it any wonder that he's completed so many DIY jobs over the years?

Charlie loves spreading his hard-won DIY experience with the world via this blog.