A Monobloc heat pump is a single unit heat pump located outside your home. It heats your water outside the dwelling and sends in the warm water to heat your home. These monobloc heat pumps would be slightly cheaper to buy and install. However, the big drawback is that you are heating your water outside the house which, in winter, the heat pump will have to work harder and therefore will be more expensive to run as the water may cool down before it enters your house.
A Split heat pump works differently to a monobloc heat pump mentioned above. A split heat pump, has the condenser (this collects the heat from the air) and sends in the heated gas (not water) into your house to what we call the indoor unit. (This is where the hot gas heats your water). The indoor unit also houses your hot water cylinder (water for your showers and taps). As all the heated water is contained within the building, the split systems would be considered cheaper to run.