Does the outdoor unit need to be installed on a concrete slab or on brackets?

To reduce vibration and the potential to rust, refrain from installing your heat pump / air conditioning unit directly on the ground and install it on a secure base. There are many different options for installing your outdoor unit. You should discuss your requirements with your installer to find the most suitable arrangement for your home. If your primary use for the heat pump / air conditioner is to heat your home, the outdoor unit needs to be mounted in such a way that condensation is able to drain from the outdoor unit.