I'm taking a guess that when you say a 05 model you mean 2005 onwards.
One basis thing springs to mind to check before getting too worried. If the pollen filter is blocked the heater blower will only put out a very poor blow to all vents. The heater will also sound as though all the vents are shut and the blow is on max. There are other probable faults, but this is one of the most common causes of the fault you describe. Oh and one of the cheapest to fix.
Another sign a pollen filter needs changing is you might find your Zafira windows steam up easily, and take a while to clear.
Pollen filters need changing at least every 2 years.