Renewable heating is any method of heating your property that extracts heat from it’s surroundings rather than burning something. This can be in the form of a Air Source Heat Pump, Ground Source Heat Pump or Solar Thermal system. They extract heat from the air, ground or daylight, run that through a refrigerant cycle to increase that heat into something useful. This process uses electricity instead of gas or oil. It greatly reduces your carbon immersions as the best gas boiler is around 90% efficient. So one unit of gas gets you 0.9 units of heat. Where as a heat pump is between 300 and 400% efficient so for every unit of electric you put in you get between 3 and 4 units of heat out. The carbon savings can be even greater when teamed up with a green energy supplier or your own solar PV system. 

The simplest way to think of a heat pump is a fridge. Imagine your home is a giant fridge that you live in. However instead of cooling like a fridge the process is reversed and the inside is warmed instead. The compressor and fins on the back of your fridge are outside therefor heat is extracted from outside to use inside. A fridge cools inside and warms the room around it with the heat its removed from inside. A heat pump does exactly this but backwards. Warms inside the house and cools outside.