Warmth helps chemical processes work more quickly and effectively. Consequently, detergents work more effectively in warmer temperatures. Hotter water gets your clothes cleaner.
Also, heat can set dyes. Therefore, sometimes clothes with dyes that run can be stabilized with hot water: Hot water can make the dye in a fabric stop running.
Finally, heat can help kill germs. Your laundry should be more sanitary if washed at higher heat. The US Centers for Disease Control specify that for sanitary purposes, laundry (they're specifically discussing linen) should be washed in a temperature of "at least 71 C (160 F) for a minimum of 25 minutes".
Use the hottest temperature in which you can safely wash your garments, in order to get the cleanest, most hygienic clothes. You can check this guide to review how to read the symbols on your clothes' care tags.
If you have a garment that has become yellowed or stained, and you're otherwise going to throw it out, I suggest you first try washing it in hot water with a quality detergent to see if it comes clean. What do you have to lose?
The temperature of your household water doesn't necessarily correspond to what the detergent manufacturer assumes it will be. Also, the temperature of the water in your washer may vary from the rest of your home, based on the length of the pipes running to it and your home's water pressure, if your washer (like most American washers) doesn't have an internal water heater. Your washer's water temperature may be cooler than the rest of your home if it's further from the water heater, or hotter if it's closer. This may cause your washer's water to be cooler or hotter than desired.
| Water temperatures in Tom's washer | |||
|---|---|---|---|
| Cold | Warm | Hot | |
| Temperature: | 64° F | 82° F | 108° F |
Your detergent is designed to clean effectively at certain temperatures. The manufacturer assumes that "hot", "warm", and "cold" mean specific temperatures of water. Here's a chart showing what temperatures your water is expected to be in your washer.
| Recommended wash water temparatures According to the Soap and Detergent Association |
|||
|---|---|---|---|
| Cold | Warm | Hot | |
| Temperature: | 80° F or colder 26.7° C or colder |
90° F to 110° F 32.2° C to 43.3° C |
130° F or above 54° C or above |
You may wish to test the temperature of your own washer's water using a thermometer, as I tested mine. Compare the results to the recommended wash water temperatures chart above. You may find that your water temperatures aren't what they're intended to be. You should use this to determine what the settings on your washer really mean.
For example, the water in my washer when I set it for "hot" is 108° F. That means my washer's "hot" wash is really a "warm" wash, so when I want to wash my clothes in "warm" water, I set my washer for "hot". That also means my washer's "warm" wash is really a "cold" wash, because my "warm" wash temperature is below the recommended temperature for "warm".
If I want to was my clothes in "hot" water... well, I can't, because my water doesn't get that hot.