Have a large bedroom window that get's very hot late afternoon sun in the peak of summer. It has basic white aluminium venetian blinds on it that from what I am aware don't offer much in the way of heat insulation or reflective properties. The portable AC has to work very hard at this time. Is there anything I could use/hang in front of the blinds to reduce heat gain other than replacing the blinds completely?

  • Venetian blinds are closed in either extreme direction. If the slats are parallel with the incoming light, some light and heat will get through even though they're closed. If you set them at the other extreme, the slats will be perpendicular to the light and block more. Beyond that, you can place thermal lined curtains in front of them. When you want the heat in the winter, open the curtains and leave the blinds parallel with the light and open a crack. You'll still have privacy, but gain heat from the sunlight.
    – fixer1234
    Jan 26, 2018 at 1:05

2 Answers 2


One option that can actually help a lot and can diy done is special window film that is made just for that purpose. I have no affiliation with this company or its products but it was a first hit in a google search just to give you an idea of what I am referring to. It looks like they have some good information on their site. https://www.allwindowfilms.com/products/solar-window-film/reflective-window-film

My experience has been with a 3M product but I can't locate the product name quickly. 3M though charges a premium for their name. Is it any better or not I can't really say. These types of films do work though. Not as well as a replacement window with low-e color reflective glass multiple panes and inert gas filling. But that gets a lot more involved.

UPDATE: I found 3M's info. https://www.3m.com/3M/en_US/home-window-solutions-us/solutions/ This is the product I would probably suggest, https://www.3m.com/3M/en_US/company-us/all-3m-products/?N=5002385+8709316+8710037+8710654+8710938+8711017+8721691+3292716663&rt=rud

  • Yes I was aware of window film but I was under the impression that you needed heavily tinted film to reduce heat gain. The 3M film PR70 suggests even the lighter tint has not much less solar rejection than the darkest tint. I would prefer the tint to be as light as possible...
    – Kol12
    Jan 26, 2018 at 3:52
  • Well that is side effect of films for sure. The more solar rejection you want the darker the tint will have to be. Even with the lightest tint at 50% solar rejection you lose 31% of visible light transmission. I am not aware of anyway around that yet on the market that will only block UV and IR wavelengths and let the quite small visible band through. Technology is developing and new products come out all the time so there may be one out there you might find with a little googling. I wish I could recommend one for you. :-(
    – C Knight
    Jan 26, 2018 at 4:27
  • 1
    I had an 8' sliding glass door in my master bedroom in my last home it got really warm in the afternoons we installed a reflective film that was tinted and it made a huge difference. Just one note just because you can't see out side dosent mean neighbors can't see in ,,, our film acted like a mirror with lights on in the room but was almost clear from the outside,,, a friendly neighbor told us OOPs.
    – Ed Beal
    Jan 26, 2018 at 6:42
  • 68% visible light transmission is not too bad with the PR70, the light should still appear quite natural. As long as it was not too dark in winter this definitely could be the solution, there's surely no harm in giving it a go. Next thing to find out is how user install-able friendly it is..
    – Kol12
    Jan 26, 2018 at 6:46
  • They can be frustrating to install without air bubbles. It is really important to not do it in a rush and follow manufacturer install specs to the letter. They don't need much in the way of tools, none of which are expensive. Some manufactures want you to use their own film slip solution. Sometimes it is a concentrate to mix water but mostly it is ready to use. 3M wants you to use an authorized dealer. But it is not really difficult to do. I might not be a bad idea though to pick up one of the cheap films they have at the building centers to practice if you are not an avid diy'er.
    – C Knight
    Jan 26, 2018 at 9:02

I'm not sure what floor your bedroom is located. Is it a first or second floor by chance? And this isn't an immediate solution. But assuming you have garden space beyond your bedroom, have you thought about planting a tree? Trees strategically and safely planted around the house can significantly reduce summer heat by providing shade for your home.

My parent's home is located on a residential side street and their living room (with a very wide and tall window) faces the street. The twenty foot tree that was cut down over a year ago truly made a difference and we didn't realize this until it was gone. Now the sun makes the front of their house so uncomfortably hot in the summer. A new sapling was put in its place but it will take a few years to gain the shade cooling effects they once enjoyed.

If it's an option, look into fast growing dwarf to midsize trees that don't have invasive roots (stay away from weeping willows - they will literally rip up your sewer drainage pipes). Ask someone at a nursery what they'd recommend.

  • A good suggestion but not possible as the room is right on the border of the house. There is room for a path but not to grow a tree. Our previous house had big trees right down the street and they did help in summer.
    – Kol12
    Jan 27, 2018 at 6:40

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