[dheera]

Capable doesn't mean it always puts out that amount of heat.

A well-designed system would have good insulation, can dump 10000W watts of heat out and bring the room from cool to toasty in 5 minutes, and then scale back and maintain the temperature after that by putting out 500W after that.

This also tends to be more efficient in practice because if you know it only takes 5 minutes to heat up you are less likely to want to leave it on when you're not around.

[organsnyder]

But it can't heat up the walls and other surfaces in that amount of time. The building will feel colder for the same air temperature setting until those objects have had time to warm up as well.