# Which uses less energy to heat a room: central steam heat, or a ceramic space heater?

My partner and I are having a friendly debate. We live in a walk-up style apartment building which has a radiator-like unit in the corner, which we believe is connected to some sort of central steam heat (ie, the steam is piped through the radiator from a central unit in the basement, which heats our house). We also have a ceramic electric space heater. We're curious which of these methods of heating our living room is more "environmentally friendly" - that is, which one will consume less energy (from the power/gas company) to increase the temperature in our living room by one degree. We're assuming that the steam is generated by a gas boiler, and the electricity by an oil-fired power plant.

This is not a straight forward question to answer.

If for example you use solar or photovoltaic energy to power up your ceramic heater then that is definitely more environmentally cleaner than any type of fossil fuel burner that could boil water in order to produce steam.

# Sankey Diagram

If you need to debate it more depth, it will be easier if you used Sankey Diagrams. They are a visual tool for getting an overview of how energy is redistributed within a process.

Sankey diagrams describe how the primary energy from any fuel gets redistributed to other types of energy (some useful some not).

# Electrical energy

A typical Sankey for energy production from fossil fuels is presented in the following image, which shows that only approximately 35% of energy is useful for electricity:

So you only get about 1/3 of the total energy for electricity. The good thing for ceramic heaters is that you have almost 100% efficiency, so all the electrical energy is converted into heating.

# Steam Boilers

The problem with steam boilers is that they are usually old installations, with limited data. Additionally, they can be very dependent on the materials used during installation and the maintenance afterwards. Generally speaking you get about 2/3 of energy in steam that you can use for heating.

# Comparison between the two.

So you can see that, while you use more efficiently the primary energy with the steam boiler, if the electricity you get is from a renewable source then the ceramic might be more environmentally friendly.

Of course, I avoid going into the discussion about carbon emissions, or the total impact on the environment (e.g. consider if your electricity came from nuclear). That makes the problem even more complex.

# A Better solution

If you live in a relatively warm climate (i.e. you don't get temperatures under 0 more that a few days per year), a better alternative for electrical power can be a heat pump.

The difference with heat pumps, is that they don't use the electrical energy directly for heating. (Simply put) What they do is they use the electrical energy to mechanically move an arrangement of pumps/compressors/condensors to pump heat energy from one side of the wall to the other. Heat energy that would not usually be inclined to flow towards that direction. More specifically, they take heat from the colder environment and pump it inside a warmer room.

That process, in ideal conditions, is very efficient. For example, for one unit of electrical energy you can nowadays move up to 4 units of heat energy. That ratio of useful energy to energy expended is the basic formula for the famous COP - Coefficient of performance. In this specific example COP would be 4.

So in ideal conditions, if you used 100 units of fossil fuel, and got 35 units of electrical energy, in theory you could get 140 units of heat energy pumped in your room.

Of course, there are limitations. E.g. at cold climates using a heat pump would create ice/frost on the heat pump, which ultimately would lower significantly the COP.

• Why Sankey diagram? Start with Power In = Power Out and then account for all losses. Always worked for us even as engineering students, along with things like Nusselt number etc Dec 19, 2020 at 16:33
• I find it tends to give an good overview of the problem. Especially, since this is a familial debate, I thought it might be helpful for a discussion
– NMech
Dec 19, 2020 at 16:42
• Well, having been involved in designing two dwellings that are super insulated, triple glazed and make lots ofuse of passive solar, never needed a diagram like that, but it’s a free choice. Dec 19, 2020 at 17:07