I change my heat bulb when it burns out or I need a higher or lower wattage bulb to get the right temps (generally as the seasons change and my ambient household temp changes). Otherwise they're good
When it is time to replace yours, just a note that you can use a regular lightbulb or a halogen flood light - all you need is something that puts out bright clear light and enough heat to get your temps in the right spot, no need to pay out extra for a petstore "heat" bulb.