Check the furniture's care instructions and leave enough separation from heat sources to avoid overheating surfaces or restricting the radiator's operation. There is no universal distance that suits every radiator, material and room, so do not treat a product photograph near a heater as installation guidance.
Consider where the cat will rest when the heating is on and whether it can move to a cooler place freely. Cushions and wooden finishes may also have manufacturer-specific heat restrictions. Keep the tree clear of controls and any access needed for maintenance. If the intended spot is beside a heater, measure the furniture's upper overhangs as well as the base, because a bed can sit closer to the heat than expected. Ask the furniture supplier for clarification if its instructions do not address the proposed location.
Assess the position with the heating operating normally, without using the cat as a test. If the resting surface becomes uncomfortably hot or bedding could touch the heater, choose another position and follow the appliance's clearance guidance.
For product comparisons alongside this advice, see Linden wooden cat tower and Arbor Retreat. The details below explain their sizes and uses.
Further reading: cats.org.uk.
Linden wooden cat tower
Arbor Retreat
Floral Canopy