Adding water to the baseboard heating system 

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Adding water to baseboard heater

Water-based baseboard heaters are quite popular in many households, thanks to their ability to provide warmth quickly and efficiently. More importantly, they provide a relatively uniform distribution of heat throughout the house. However, these systems require a little maintenance like adding water to the baseboard heating unit to keep them running efficiently. To understand why this is important, let’s start by looking at how hydronic/water-based baseboard heaters work! 

How water-based baseboard heating systems work! 

Since hydronic heating systems are closed, water is constantly circulating through their pipes and into the boiler. However, newer units have several zones with 2 water pipes connected to each zone. One of these pipes circulates warm water to the rooms, while the other returns the much cooler water to your boiler for reheating. On the contrary, in the older one-pipe models, heated water flows to each room and back to the boiler using the same pipe. As a result, the last room rarely got as warm as the 1st room. 

As for the boiler, it’s either powered by natural gas, oil, or propane. In addition, the system features a pump that circulates the warm water as streams to the baseboards near the floor of the exterior walls throughout the house. This ensures that temperature across a properly functioning hydronic baseboard heater remains uniform over its entire dashboard. 

On the downside, sediments and sludge tend to accumulate in the baseboard heating system’s pipes over time. As a result, this reduces the flow rate of water through the baseboard, affecting the heating system’s efficiency. For that reason, it’s important to drain and refill your baseboard heating system at least once a year to flush the debris from the pipes, expansion tank, and baseboard heaters. Best of all, this will keep your system dirt-free to ensure effective and uniform distribution of heat throughout your home. 

But, how do you go about it? Well, let’s find out! 

How to drain and add water to hydronic baseboard heating systems 

Adding water to the baseboard heating system is a relatively simple task. However, like any other DIY project, you’ll need to gather the right tools before you start the task. Some of the items you’ll need include; 

  • Screwdriver set (Phillips screwdriver/ flat screwdriver)
  • Adjustable wrench 
  • Garden hose 
  • Bucket
  • Small dish 

In addition, make sure you give the system enough time to cool down before you drain the boiler. Otherwise, you may get severely scalded when you open the valves if the system has any hot water. With that in mind, let’s get it to the actual process, step by step; 

1. Preparation 

Turn down your baseboard heater thermostat to a low setting and turn off the power supply to your boiler/ furnace. Some furnaces/ boilers are turned off at the fuse panel or circuit breakers, but some have a simple On/ Off switch. Whichever the case, make sure the power supply to the boiler is turned off and wait for about 2 hours for the system to cool off before you move on to the next step. 

2. Locate the heat valve 

Find the water inlet pipe that connects the boiler to your house water supply pipes. The heating valve is usually located on the supply pipe. Once you’ve identified the valve, turn it off by rotating it clockwise using a wrench. 

Next, look for the system drain valve/ boiler drain, which is a garden hose threaded faucet. This drain is usually found near the bottom of the boiler, either connected to the boiler or a pipe. 

3. Connect a garden hose to the drain valve 

Connect the garden hose to the drain valve on the boiler and run it to a floor drain. Slowly turn the knob counterclockwise with a hex or slotted screwdriver to open the boiler drain. To prevent leakage on the valve, place an absorbent material over the nozzle while draining the water. Also, put a bucket right under the nose of the nozzle to prevent a lot of spills on the base. Let the water gurgling out of the hose, keeping a safe distance since the air or water coming out of the system might be a little warm.  

After a steady stream of water flows out of the system, it will stop draining out. This shows that air or sediments and debris that was in the heater’s hydraulic system have been removed. When that happens, you can remove the garden hose and close the drain valve. 

4. Turn off the drain valve 

Turn the drain fitting clockwise to close it and turn the hose fitting counterclockwise to remove it from the boiler. Put in all the screws in the relevant slots and use a screwdriver to tighten them up.  

5. Refill the tank 

Connect the female fitting of the garden hose to the drain valve of the expansion tank. The drain valve is usually located on the bottom of the tank in older expansion tanks, but modern tanks use a diaphragm. 

All in all, after connecting the garden hose to the tank, turn the handle of the drain fitting counterclockwise to open the valve. Once the water stops flowing out of the garden hose, close the tank’s drain valve and disconnect the garden hose. 

Next, find the baseboard heater near the boiler and open its bleeder valve to expel air from the system. Put a small dish near the valve to catch any water coming from the system. Once the air is purged, water will freely get out of the system through the valve. Wipe any water that might have spilled on the floor and repeat the purging system with each baseboard heating unit. More importantly, make sure you shut down the drainage valve once the water has been drained out of the baseboard heaters. 

6. Turn on the boiler’s power supply 

Use an adjustable to turn the boiler’s gas valve clockwise to turn it on. Then turn on the power supply or circuit breaker to the boiler to power it up. After that, turn up your home thermostats until the heater starts up and check if your baseboard heaters are becoming warm. 


After following all the steps I’ve listed above, you can now start your water-based baseboard heating systems to start enjoying the warmth in your home. Also, make sure you drain and add water to your baseboard heating systems at once every year to keep it running efficiently. Ideally, you should undertake this take before the winter season to ensure your house has adequate warmth during the cold season. 

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