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House Hotter Than Outside? Where the Heat Gets In

Sun through the glass, a hot attic and stored heat can leave your home hotter than the air outside. Block the sun first, then add thermal curtains.

By Jamilur Rahman Updated November 5, 2026 · 7 min read

Time
15 min a day
Cost
$20-$50
Difficulty
Easy
A living room in late afternoon with strong sunlight coming through a large window and across the sofa and floor
In this guide
  1. Quick answer
  2. Free vs. permanent fix
  3. What you'll need
  4. Why it happens
  5. Try this first (free)
  6. When free fixes aren't enough
  7. Buy the fix
  8. Which window to cover first
  9. When heat becomes a health risk
  10. What to skip
  11. FAQ
  12. Related problems

Quick answer

Why is my house hotter than outside? Sun pours in through the windows, the roof and walls soak up that heat, and a shut-up house keeps it in after the air outside cools. Close curtains on sun-facing windows before the sun hits, open the house at night and cut indoor heat. If one window or room still runs hot, thermal blackout curtains block far more heat than blinds or thin drapes.

Free fix vs. permanent fix

Free fix · 15 minutes a day

Shade, night venting and less indoor heat

  • Close blinds and curtains on sunny windows before the sun reaches them
  • Keep windows shut by day, open them at night when it is cooler outside
  • Move the oven, dryer and dishwasher to the evening
  • Use a fan in a window to push hot air out

How long it lasts: It works as a daily routine and slows the heat. It cannot undo a hot attic or a big west-facing window.

Most readers choose Permanent fix
Thermal blackout curtains (illustration)
Illustration

Thermal blackout curtains

Most of the heat in a hot room comes through the glass. A thick, lined curtain with a reflective or foam backing, hung close to the window, stops it after it gets past the glass. The US Department of Energy says medium-colored drapes with a white plastic backing can cut heat gain by about a third.

How long it lasts: Years. They block sun every day without you doing anything beyond closing them.

Check price on Amazon

As an Amazon Associate I earn from qualifying purchases.

What you'll need

  • Existing blinds or curtains

    Close them before the sun hits, not after the room is hot

    You have it

  • Phone weather app

    Shows the outdoor temperature so you know when to open up

    Free

  • Box fan

    Set it in a window facing out to push hot air away

    You have it
  • Our pick
    Thermal blackout curtains (illustration)
    Illustration

    Thermal blackout curtains

    Measure the window and add width so the curtain overlaps the frame

    Check price
  • Removable heat-blocking window film (illustration)
    Illustration

    Removable heat-blocking window film

    For windows where you cannot hang curtains

    Check price

Why it happens

1

Sun coming through the glass

Glass lets sunlight in, and the sunlight turns into heat on floors, furniture and walls. East windows heat up in the morning, and west windows get hit hardest in the afternoon.

2

A hot attic and roof

A roof in full sun can get much hotter than the air outside. That heat moves down through the ceiling, so top-floor rooms run warmer, especially with thin attic insulation.

3

Stored heat in walls and floors

Walls, concrete and brick soak up heat all day and give it back in the evening. That is why the house can stay warmer than the air outside after sunset.

4

Heat made inside the house

An oven, a dryer, a dishwasher, electronics, old bulbs and people all add heat. In a small, shut-up home it adds up fast.

5

A closed house with no airflow

With windows shut all night, the stored heat has nowhere to go, so each day starts hot and ends hotter.

Try this first (free)

Do these in order, starting with the simplest.

  1. Check inside against outside

    Tool used: Phone weather app

    Look at the outdoor temperature at about 3 p.m. and again at 9 p.m., then compare it with indoors. If inside is warmer after dark, the house is storing heat and you should vent it at night.

  2. Shade sun-facing windows early

    Tool used: Existing blinds or curtains

    Close blinds and curtains on east windows by mid-morning and west windows by noon. Do it before the room heats up, because it is much harder to cool after the fact.

  3. Keep the house shut by day

    Close windows once the outside is warmer than inside. Opening them in the afternoon just brings more heat in.

  4. Open up and push the heat out at night

    Tool used: Box fan

    When the air outside drops below the air inside, open windows on opposite sides. A box fan in one window facing out pulls cooler air in through the others.

  5. Move the heat makers to the evening

    Run the oven, dryer and dishwasher after dark or in the early morning, swap old bulbs for LEDs and switch off electronics you are not using.

  6. Cover the worst window properly

    Tool used: Thermal blackout curtains

    Hang thermal curtains as close to the glass as you can, wider than the frame and long enough to reach the sill or floor. Keep them closed all day on that window.

    Thermal blackout curtains (illustration)
    Illustration

    Tool for this step

    Thermal blackout curtains · Measure the window and add width so the curtain overlaps the frame

    Check price on Amazon

When free fixes aren't enough

If you do the free steps and one window still lets in hot sun all afternoon, the curtains you have are not blocking enough, and thermal blackout curtains are the fix. But curtains only handle heat that comes through the glass. If the top floor is far hotter than the ground floor and the ceiling feels warm to the touch, the attic is the main source. That means better insulation and ventilation, and an energy audit or a roofer can check it.

Buy the fix

Still stuck after the free fixes? These are the products we would look at.

Our picks compared
PickProductFixesWho it's forBuy
Best pick
Thermal blackout curtains (illustration)
Illustration
Thermal blackout curtains
sun heat coming through the glass Anyone with a sunny east or west window, especially a bedroom or a room that is the hottest in the house. Check price
Budget pick
Removable heat-blocking window film (illustration)
Illustration
Removable heat-blocking window film
sun heat on windows where a curtain will not work Renters and windows where you cannot hang a curtain, such as a small bathroom or stairwell window. Check price
Upgrade pick
Reversible window fan (illustration)
Illustration
Reversible window fan
stored heat that stays after dark People who sleep in a room that stays warm all night and have a window that opens wide. Check price
Best pick
Thermal blackout curtains (illustration)
Illustration

Thermal blackout curtains

Fixes: sun heat coming through the glass

Look for: Multiple layers or a foam or reflective backing, and a label that says thermal or insulated; A light backing on the side facing the window; Enough width to cover the frame, ideally about 1.5 to 2 times the window width; Long enough to reach the sill or floor.

Who it's for
Anyone with a sunny east or west window, especially a bedroom or a room that is the hottest in the house.
Honest downside
The heat comes mostly from the attic, or the window gets little sun. Curtains will not change much.
Check price on Amazon
Budget pick
Removable heat-blocking window film (illustration)
Illustration

Removable heat-blocking window film

Fixes: sun heat on windows where a curtain will not work

Look for: Reflective, not just tinted; Removable or static-cling, so it is renter-friendly; A listed fit for your glass type.

Who it's for
Renters and windows where you cannot hang a curtain, such as a small bathroom or stairwell window.
Honest downside
You have double-pane or special coated glass. Check the film maker's notes first, since some films are not meant for it.
Check price on Amazon
Upgrade pick
Reversible window fan (illustration)
Illustration

Reversible window fan

Fixes: stored heat that stays after dark

Look for: An intake and exhaust setting, so you can push heat out at night; Adjustable panels to fit your window; Speeds that stay quiet in the bedroom.

Who it's for
People who sleep in a room that stays warm all night and have a window that opens wide.
Honest downside
The air outside is hotter or smoky, or the window will not open wide enough to hold the fan.
Check price on Amazon

As an Amazon Associate I earn from qualifying purchases. We don't show prices because they change, so use the button to see today's price.

How we picked: How we picked: this page is based on US Department of Energy window-covering advice, home cooling guides and what owners report in reviews of thermal curtains. We do not test products by hand.

Which window to cover first

  • West-facing: the worst in the afternoon and evening, the hottest hours.
  • East-facing: strong morning sun that warms the room before noon.
  • South-facing: heavy sun at midday in summer.
  • North-facing: gets little direct sun, so cover it last.

When heat becomes a health risk

Babies, older adults and people with heart or lung conditions can get sick from heat even indoors. If anyone feels dizzy, sick or confused, move them somewhere cooler and get medical help if it does not pass. If indoor air is in the 90s degrees F, a fan alone is not enough. Go to a cooler place, such as a library or a friend's home.

What to skip

Cracking windows by day and thin dark curtains

Opening windows on a hot afternoon lets more heat in. Thin sheer or dark curtains hang in the sun and warm up, then radiate that heat into the room. Pick a light, lined, thicker fabric and keep the window closed during the hot hours.

Frequently asked questions

Why is my house so hot?
Sun through the windows is the biggest source. After that come a hot attic, heat stored in the walls and the oven, dryer and electronics you run inside. A house with no night airflow also starts every day already warm.
Why is my room the hottest in the house?
It is usually on the top floor, has big west or south windows, sits above or beside the kitchen or has a door that stays shut so air cannot move. Shade that room's windows first, since that is where most of the heat comes from.
Why is my house hotter inside than outside at night?
The walls, roof and floors store the day's heat and release it slowly. Until you open the house to cooler air and push the warm air out, the inside can stay warmer than outside for hours.
Do blackout curtains really make a room cooler?
Yes, when they cover a sunny window. They stop sun from heating the room. They will not cool a room that is hot from the attic or from heat made inside, and they work best when kept closed all day.

As an Amazon Associate I earn from qualifying purchases. Affiliate disclosure

Thermal blackout curtains (illustration)
Illustration

Our pick: Thermal blackout curtains

Check price