The black Huawei brand Unifi Broadband Termination Unit (BTU) has a metal casing. This BTU is supposed to work 24x7, and when you touch on its metal surface, you will feel some heat.
I use a Vztec NC2165 notebook cooler as its cooling solution. After installed, when you touch the BTU metal surface again, you will feel it is cool.
This Vztec NC2165 is USB powered. You can find one USB port in front of the Dlink DIR-615 Unifi Residential Gateway (RG), which can be a good choice for its power source. Alternatively, you can use any available USB port as its power source.
There are many USB powered notebook cooler in the market, most are just too big for this Unifi BTU, and their fan(s) might not match with the place of the BTU ventilation holes on top. As you can see in the picture, this Vztec NC2165 just suit perfectly, and it cost only RM15.
If you are also using Unifi HSBB, I recommend this inexpensive BTU cooling solution for you.