How Do Hot Water Baseboard Heaters Work?

hot water baseboard heater

Baseboard hot water heating systems, as their name implies, are typically installed at the baseboard or, at the very least, a point low to the ground. Since heat naturally rises, placing the heating element at the lowest point in a room is an easy way to evenly heat the air in a space.

A unique benefit of using a water based heating system that relies on no form of forced ventilation is the amount of dust that travels through the air in your home will be lower than in a home where a central air conditioner is blowing air through the vents.

If the idea of using water to heat the air in a room still seems odd to you, the following information should clue you in on how hydronic baseboard heaters work and how to deal with any problems that could arise.

How it Works


The hot water in the system is obtained from a boiler in a utility room, and this boiler is heated by gas, oil, or electricity. The hot water is pumped through a system of pipes that are installed in the baseboard. The heat from this hot water is transferred to the room, and once the heat transfer has cooled the water down again, it's piped back to the boiler room, replaced by a fresh influx of hot water, and reheated.

The hot water pipes on these baseboard heaters are typically made of copper and are uniquely fin-shaped to ensure faster dissipation of heat from the surface of the pipe. This radiator type structure is similar to the construction of radiators you would find in automobiles.


The quantity of water in baseboard hot water heating systems needs to be kept at a constant volume, and any loss of water has to be compensated from an overhead tank that contains the water storage. The functioning of the boiler is connected to thermostats in the room or rooms being heated and when the temperature reading on these thermostats are increased a signal is sent which heats up the boiler and activates the pump to send water to the area demanding the heat.

Common Issues and Solutions

These are some of the issues that your may run into when using a baseboard hot water heater. To be clear, neither of these circumstances are malfunctions or result from misuse. They are simply the unavoidable drawbacks that come bundled with this sort of heating process, though they do have clever workarounds you can employ.

Heat Inequities

thermostat reading 82 degrees

Quite often the pipes or radiators are installed in rooms arranged in series. This means that rather than each room having its own unique line to the boiler, all the water travels along a common path to each room. As such, you'd expect the first radiator to experience the maximum heat and the last heater on the path to receive water that is markedly less hot.

One common solution to this issue is to control the flow and quantity of water that is allowed to reach the first radiator in the series, allowing the quantity for successive radiators to increase progressively.

To ensure equal heating in all areas, a certain amount of adjustments have to be made. However, these adjustments aren't always limited to the baseboard heater system itself. Sometimes something as benign as an item of furniture being in the wrong spot will cause it to absorb heat and impact the temperature of the entire room.

Getting the most out of your baseboard hot water heating system often means going through a trial and error stage that involves adjusting everything from your water flow to your floor plan.

Expansion Problems

Much like the previous issue of unequal heat transfer, expansion problems are also a result of the naturally occurring scientific properties of water and heat. In this case, water that is heated enough occupies a larger volume, or expands and requires more space than it does when cool in its initial space. So how do you fit the expanded hot water that's returning back into that smaller space?

You can work around this by allowing the returning water to first go through an air vessel to take care of the increased pressure, which compresses the air till pressure gets equalized. Problems can still arise if the air vessel gets full of water. Since water is not compressible like air, the buildup of pressure from the hot water can cause leakages. An expansion valve preset to the designed pressure can take care of this problem.

Problems in a Baseboard Heater

In addition to the physics quirks already mentioned, another way these systems can go haywire is through actual mechanical malfunctions or component failures.

Problems in a hydronic baseboard heating system can stem from pump failure, boiler shutdown, leaks in the system, air entrapment from the heated water, excess pressure, noise causing gas bubbles, and clogged radiator or fin units.

While that sounds intimidating, each of these problems can be solved or easily prevented with regular maintenance to your system. By making the proper adjustments at the right points, your baseboard hot water heater can have a long, active lifetime.