This is a RustEZ feature where players can merge one or multiple of the same entities into one for the sake of reducing server overload where at the same time not losing productivity.
Upgrading
For the most part, levels 1 through 10 only require one of the same placed item with no additional Net Worth.
Furnaces
Level 1 to 10: requires 1 item with no additional Net Worth required
Level 10 to 15: requires 1 item and 2,500 Net Worth
Level 15 to 20: requires 1 item and 5,000 Net Worth
Water Pumps and Purifiers
Level 1 to 5: requires 1 item with no additional Net Worth required
Level 5 to 10: requires 1 item and 1,000 Net Worth
Level 10 to 15: requires 1 item and 2,500 Net Worth
Level 15 to 20: requires 1 item and 5,000 Net Worth
Water Catcher
Level 1 to 10: requires 1 item with no additional Net Worth required
Level 10 to 15: requires 1 item and 1,000 Net Worth
Level 15 to 20: requires 1 item and 2,500 Net Worth
Water Barrel
Level 1 to 10: requires 1 item with no additional Net Worth required
Level 10 to 15: requires 1 item and 1,000 Net Worth
Level 15 to 20: requires 1 item and 2,500 Net Worth
Composter
Level 1 to 10: requires 1 item with no additional Net Worth required
Level 10 to 15: requires 1 item and 1,000 Net Worth
Level 15 to 20: requires 1 item and 2,500 Net Worth
PSA: When upgrading to the maximum level, all electrical entities receive a free level of power consumption. This means that level 20 multiplies everything, except the power usage, using the same amount as a level 19 entity.