The Low-Cost Solution That Can Effectively Reduce Heat In Your Garage This Summer

Typically, the hottest time of the year for Americans living in the lower 48 states occurs during the summer months of July and August. If you do hobbies, or work, in your garage or even if your laundry appliances are located there — it can be positively scorching. Especially since temperatures inside a garage can be 10 to 18 degrees Fahrenheit warmer than the outside air.

One option to cool things down is a portable air conditioner. However, there's the initial cost of buying one, which can be hundreds of dollars, not to mention the unit will run up your electricity bill while in use, something that can be particularly devastating for those that live in states with higher electricity bills. A more affordable, and eco-friendly, alternative is to insulate a significant source of your garage's heat, your garage door. With that said, sheets of rigid foam insulation aren't exactly cheap to purchase — unless you get creative, that is. 

The foam boards that are sold at a cheaper retailers, like Dollar Tree, aren't technically intended for insulating your home. They're more typically purchased for arts and crafts projects. However, in between the outside layers of kraft paper resides a core made from polystyrene foam – an excellent insulator. The air pockets within the foam can trap heat and prevent it from entering your garage.

The sheets, which are sized 20 inches by 30 inches, are available for $1.25 per sheet online or in-store at your local Dollar Tree. Reportedly, some stores also stock a 25 pack of the sheets for $20, which doesn't save any money but can be more convenient while also reducing packaging waste. Each sheet covers exactly 4.17 square feet, so you'll want to measure your garage door in advance to calculate exactly how many sheets to buy. As a rule of thumb, single garage doors are frequently 8 or 9 feet wide by 7 feet tall. For two-car garages with one large door, the most common size is 16 feet wide by 7 feet high.

For comparison, a purpose-made garage door insulation kit from Home Depot costs $52.18 for a single-width door, as of June 2025, and covers 60 square feet. Dividing $52.18 by 60 square feet yields a per-square-foot price of $0.87 for the Home Depot option versus just $0.30 per square foot for the DIY Dollar Store solution. While there are many clever ways to save money at Home Depot, in this instance it's not your best choice.

As far as installing your bargain garage door insulation, you'll need a few other tools and supplies. To begin, a ladder or step stool to reach the upper sections of the door, plus a utility knife, and ideally some sort of straightedge to cut the foam sheets cleanly. If you don't have a dedicated straightedge, items like a ruler or scrap of lumber may suffice. Use a tape measure to determine the size of each garage door section between its horizontal beams.

It's also worth mentioning that some garage doors will have a pattern of many individual "squares" while others will have four or five long panels instead. Similarly, the amount of bracing on the inside of the door where you'll be insulating will vary by design and region. For example, garage doors in hurricane-prone Florida with its expensive home insurance will have considerable extra metal bracing in order to withstand high winds. You will need to work around such framework when cutting your foam sheets to size.

Once you've devised a system to cut the foam boards so they fit snugly in place, make sure they stay put by using duct tape, or something similar, to fasten the sheets to the inside of the door and seal any seams. Truly ambitious types can use a double layer of foam boards for extra insulation, if desired. Luckily, this trick is so affordable that, even with a second layer, the cost will still be lower than purpose-made products.