Simply insulating the length of beer hose from the refrigerator to the tower will cause problems. Even a few inches of beer hose that is not kept at 36-38°F will result in foam and promote sour/cloudy beer.
(See What temperature do I need to store draft beer at?
Dispensing Draft Beer from a tower located on a counter top just a few inches directly above your home refrigerator (or freezer) is quite simple. Imagine that when a tower is mounted directly on top of a refrigerator, the cold air within the refrigerator circulates within the tower and helps maintain the beer at the critical 36-38°F temperature all the way to the point of dispense. When mounting a tower on a counter top just a few inches above a refrigerator, the easiest method to maintain this 36-38°F temperature is to create a duct that also allows the cool air to circulate with in the tower.
Creating Air Duct
The most common type of draft beer tower is a 3" diameter column tower. If this is the type of tower you have, then using a 2-1/2” hole saw, drill a hole in the counter top where the tower will be mounted and through the top of the refrigerator where it will be directly below the hole in the counter top.
To do this, it is recommended to purchase a length of 2" PVC pipe at your local hardware store. The outside dimension for 2" PVC is 2-3/8". Then measure and cut a length to fit between the top of the refrigerator and then flush with the top of the counter. Using silicone to seal the joints and prevent any leakage of the cold air that will be circulating through the pipe. By doing this, you will create a simple extension as if the tower were still mounted directly on top of the refrigerator. Thus allow the cold air circulation from within the refrigerator up into the tower to help maintain the 36-38°F beer temperature all the way to the point of dispense.
This size of PVC pipe will allow the maximum amount of space for the cold air from the refrigerator to continue to circulate within the tower.
In such a system, the temperature of the dispensed beer should be monitored. This is to assure there is enough air circulation within the tower to maintain the 36-38°F temperature is being maintained all the way to the point of dispense.
To check the dispense temperature, simply pour a beer into glass and use a thermometer to read the temperature. This should be compared to the temperature of the beer within the refrigerator, and these temperature should be identical.
If the temperature of the beer being dispensed from tower is warmer then in the refrigerator, then the air circulation within the tower is inadequate.
If this were an issue, to correct it would require the installation of a small blower fan within the refrigerator.
One end of a short length of hose is connected to the blower, and the other end extends up into the tower to create cold air circulation.