You don’t have to install thermal insulation (other than what’s required according to the building code).
But this means that vast amounts of heat will escape to the surrounding environment where it’s colder (such as the outside air, the ground below, other solid structures nearby)… this is where the heat wants to naturally travel to the most – where it’s coldest.
Therefore, preventing the heat from travelling to where you don’t want it to go – and directing it into the rooms where you do want to heat – will ensure your system heats as you would like it to, within the running cost that you expect.
