Why Is My Room In The House So Hot At Night?

When the sun goes down, it’s only reasonable to expect that your home will cool down as well. But, unfortunately, some people still experience a high temperature in their bedroom well into the night. So, why is your bedroom in the house so hot at night?

Your bedroom’s position affects its night-time temperature. South-facing bedrooms experience more direct sunlight and heat up during the day. That heat re-radiates into the room at night, keeping it hot. The same happens at night as heat rises through the home, passing bedrooms on upper floors. Poor ventilation and a weak AC system can keep temperatures raised. Lastly, heat from the attic can also infiltrate downward into your room.

In the following sections, we’ll explore the reasons why your bedroom in the house is so hot at night. Plus, we’ll also help you understand what you can do to resolve each of those causes.

Related: Why Is My Room Hotter Than Outside?

Bedroom Position 

The position of your bedroom plays a very significant role in how hot it feels at night. That’s especially true for bedrooms on the upper floors or those on the South-facing side of the house.

When it comes to the position of your bedroom, there are two factors at play here: solar heat gain and the Stack Effect.

1. Solar Heat Gain (South-Facing Bedrooms)

Bedrooms that have south-facing windows or doors tend to get very hot in the daytime. These rooms are exposed to plenty of direct sunlight, which heats the floors, walls, and other things in that room.

During the day, those surfaces absorb and retain heat. At night when there’s no more direct sunlight, however, those surfaces start to re-radiate the heat back into the room, making it very hot.

What you can do about this:

Changing the position of the windows, doors, or the bedroom itself is too challenging, if not impossible. Instead, you can reduce or eliminate solar heat gain by blocking out direct sunlight.

The most straightforward solution is to keep your blinds closed during the day. Besides that, you can also invest in window tinting films that reflect solar heat outwards, preventing most of it from entering the bedroom in the first place.

2. The Stack Effect (Upper Floor Bedrooms)

Another way your bedroom’s position makes it hotter is the Stack Effect. That is a phenomenon that affects rooms located on the upper floors of the home. 

Simply put, heat must rise through the house towards the attic to escape through the ventilation system. Unfortunately, that heat will need to pass through the bedrooms located on the upper floors.

As a result, those bedrooms (including yours) will feel hotter, especially at night.

What you can do about this:

The Stack Effect is caused by air that moves upwards from the lower levels and through the attic. To prevent this, you’ll need to stop any air from entering the home from the lower levels, i.e. making the lower floors airtight.

That includes air sealing and insulating sections of the house where air leaks inwards, like windows and doors. When air stops flowing into the home, there will be less hot air flowing upwards through your bedroom.

Poor Ventilation

Another reason your room is so hot at night is poor ventilation, both in your bedroom and in the attic. In both of these spaces, air must always be allowed to flow smoothly. That will allow hot air to flow out of your bedroom before being replaced by cooler, fresher air coming in.

Without proper ventilation, the hot air will increase and remain trapped in your bedroom. All of this heat originates from your body (and anyone else in the room), as well as from electrical devices like computers and TVs.

Besides that, poor attic ventilation will also cause the attic to heat up. When the attic gets hot and cannot vent that hot air to the outside, some of that heat will escape downwards into your bedroom and raise the temperature. This process is called ‘infiltration’, and we’ll look at it much closer in the next section.

What you can do about this:

A lack of ventilation in your bedroom or attic means that there is a problem with the ducting responsible for creating airflow. Over time, ducts may become clogged or kinked. Plus, the vents themselves might be blocked by large objects like furniture or boxes.

To fix this, you can begin by ensuring that nothing is blocking the vents in your bedroom. Then, you can inspect the ductwork to ensure that there are no kinks or blockages. Lastly, it might be time to clean your vents yourself or by hiring an HVAC professional.

As a temporary solution, while you clean your ventilation system, you can also leave a window or door open to increase airflow. That will help you increase airflow and lower your bedroom’s temperature.

Infiltration

Earlier, we saw how poor ventilation in an attic could cause it to heat up. That happens in the daytime when there’s plenty of direct sunlight landing on your roof. An attic with poor ventilation will retain that heat even after the sun goes down.

Unfortunately, if that heat can’t escape upwards, it will naturally radiate downwards instead. The term for this is ‘infiltration’ when heat from an attic slips through cracks and openings to heat up the bedrooms underneath it.

What you can do about this:

Infiltration from the attic happens through any openings between that space and your bedroom. So, things like outlets, supply registers, and any lighting fixtures in the ceiling must all be correctly sealed.

In doing so, you’ll keep the attic completely separate and sealed off from your bedroom. 

You can more effectively solve this problem by also resolving any issues of poor ventilation. When both the attic and your bedroom are well-ventilated and sealed off from each other, infiltration will no longer be an issue.

Thermal Mass

In the simplest of terms, ‘thermal mass’ refers to how much heat a material can retain. For example, some home-building materials like brick and concrete are high thermal mass, which means that they absorb and retain plenty of heat.

Suppose the structure around your bedroom is made of materials with high thermal mass. If that’s the case, then the structure will absorb plenty of heat when exposed to direct sunlight during the day.

At night, that structure will radiate the heat back into your bedroom, causing it to feel very hot.

What you can do about this:

Unfortunately, you can’t change the thermal mass properties of the materials used to build your house. What you can do, however, is to invest in better insulation.

Proper insulation will prevent the structure around your bedroom from heating up excessively in the first place. That way, there will be no heat that radiates into your room at night.

Air-Conditioner Is Too Small

If your HVAC system includes an air-conditioner yet your bedroom still feels hot at night, then the problem might be with that AC system instead. Here are some possible AC-related reasons why your bedroom is too hot at night:

  • The AC isn’t working: To begin troubleshooting this issue, ensure that your air conditioning system is working correctly. It’s possible that your AC is blowing warm air and requires maintenance.

Air conditioning systems also have filters that must be cleaned regularly to ensure that they can supply your bedroom with cold air.

  • Poor ductwork: Earlier on, we looked at how poor ductwork and ventilation could cause your bedroom to feel hot at night. That also affects your AC system, as the cold air it generates will not be able to reach your bedroom if the ductwork and vents are clogged, blocked, or kinked.
  • The AC system is too small: Regardless of the type of AC you use (whether centralised or an individual unit in your bedroom), it must be of the correct size to efficiently cool your bedroom.

It’s not unusual for some buyers to mistakenly purchase a system that’s too small for their home or bedroom. Unfortunately, when this happens, the room takes far too long to cool down. Combine that with any of the other factors mentioned in this article, and what you end up with is a bedroom that’s too hot at night.

What you can do about this:

Firstly, ensure that the AC system you have for your home is sufficient for the space that it needs to cool. If it isn’t, then you’ll need to consider upgrading it or purchasing a separate unit for your bedroom.

Related: What Type of HVAC System Do I Have?

Besides that, you must also troubleshoot the AC system and make sure that it is indeed blowing cold air. AC systems also have removable filters that must be cleaned regularly to ensure optimal airflow. 

Lastly, you’ll need to inspect any ductwork connected to your AC system. Fix any kinks and clean out any dirt that might be restricting airflow. And, of course, make sure that none of the vents are blocked by things like furniture, boxes, or any other large objects.