Previously we’ve written about keeping doors closed if you have central heating with heat emitters or radiators in every room (see zoned heating). For this to reduce energy use and costs we need to regulate temperature in every room. A simple system (without zoned heating) might have Thermostatic Radiator Valves (TRVs) on each radiator or heat emitter and a single room thermostat (often in the hallway or main room). A more complex zoned heating system might have room thermostats in each room. These thermostats prevent the room temperature exceeding the desired temperature for that room or zone. This can be an effective way of saving energy and reducing bills without needing to change the system. Using less energy means there is less pollution and lower climate-warming carbon dioxide emissions. If you have a simple system with no TRVs on any radiator then getting them added could help you lower your heating bill quite significantly if you then go on to use them as we will now show.

How much could be saved using room thermostats or TRVs? First consider what a comfortable temperature in winter might be for different areas. We often prefer a warmer temperature in our main living areas than in say the kitchen or bathroom. Bedrooms can be a little cooler too. Perhaps 20°C in our main living space, 18°C in bedrooms and dining room, 16°C in the kitchen and bathroom. Consider a modern apartment as an example with external wall U-values of 0.5 W/(m²K). To make things simple let’s assume there is no heat loss down to the apartment below or up to the apartment above. We only need to look at heat loss out of the walls. Consider the case when the outside temperature is freezing (0°C) and the stairwell is at 10°C. The heat loss is given by the area of the wall multiplied by its U-value multiplied by the temperature difference across it (see our U-values article for more detail). As shown by the images below, the total heat loss for the original case of having 20°C everywhere is 855 W. What does that cost? With gas prices currently capped at 6.33p/kWh this is equivalent to £1.44 per day (with a 90% efficient gas boiler). If we had used the TRVs on the radiators, the total heat loss reduces to 732 W which costs £1.24 per day. A 14% saving. 14% gas saved. 14% cost saved. 14% emissions saved.