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Forced Hot Water Baseboard Heating Systems Explained

By Edited Nov 13, 2013 1 0

Hot Water The Only Way To Heat

Hot water heating system
"Forced hot water baseboard heating systems explained," Is an article that will help anyone understand how a hydronic system works. 

We'll walk through from the boiler to the flue pipes, and everything in-between. Read on to learn all about your forced hot water heating system.

Even if your not mechanically inclined and you never intend to work on the heating system in your home, you should learn enough to pass on helpful info to any service people you may need to call.

Learn the tell tale signs of problems that arise in this type of heating system. We'll also take a look at some easy maintenance tasks that anyone can perform.

Forced Hot Water Baseboard Heating System Series of Operation

Just how does it all work?

Ever wonder exactly what happens when you turn up that thermostat? You may have a digital programmable thermostat, or you may have a simple round Honeywell model that has a dial. Either way when you turn it up, or when the room temperature drops below where that thermostat is set, stuff is going to begin happening.

This is where the mystery begins for many homeowners. The working parts of a hydronic system are meant to do their job quietly, behind the scenes. 

The parts that you never see, unless you forage into the basement or garage, or wherever they've hidden the guts of your system are what makes it all work. This section of the article will run you through.

When You turn up the thermostat.

A circuit closes and sends a message to a switching relay at the boiler. This relay is electrical and when it receives the message that a room needs heat it will relay that message to the main boiler control as well as the circulator pump that makes hot water run through the baseboard for that zone.

Some heating systems are only one zone, or loop. Some heating systems have many zones. If you have more than one zone you will have multiple thermostats tied to their own relays. These relays are tied to their respective pump which is how the system knows where to send the heat.

When the relay calls. The system will call the boiler. The boiler will fire and begin to heat the water in the system. 

As this water is heated by the boiler, it's also being circulated through the piping to the baseboard heating for that zone and then back to the boiler.

The boiler will continue to fire until the water reaches the high limit setting (Usually around 200 degrees) or the temperature in the room rises above the thermostat setting, or somebody turns it down.

Circulator pumps will run continuously until the thermostat is satisfied. The boiler however may come on and off as the water temperature falls from the heat transfer that happens during it's ride from the boiler around the zone and back to the boiler.

Each zone will be a loop around the home out to a room, or rooms and back to the boiler. There are a few other items you'll find installed along the way. Some of them will be found in multiples according to how many zones the system has.

Circulator pumps are an example of multiples you may find piped up at the boiler in a manifold. Some systems use a pump for each zone. Some systems however may have one larger pump running the whole system and several electric zone valves that run each zone. 

Zone Valves are basically installed in-line as the piping leaves the boiler heading out to each zone. This electric valve opens when the thermostat for it's respective zone calls for heat, the boiler fires and the main circulator pump starts to circulate heated boiler water through the open zone valves and out to the rooms.

Flow checks are usually found in the feed line as the manifold splits the zones. They prevent a gravity feed from rising up into zones that are not calling for heat. If one sticks open while another zone is calling for heat, you'll overheat the rooms with the stuck flow check. This happens because the hot water rises all on it's own if left uncontrolled. 

Auto Feeders and Backflow preventers will be found on the feed line coming from the city water to fill the system Or they may tie into the well line if you have your own well. Either way these valves will be common to most systems.

The Auto feeder keeps the water pressure in the system at a set point. Most systems run between 12 and 25 pounds per square inch. If a leak should occur anywhere in the system, the autofeeder will put back water to keep the pressure up.

Backflow preventers do exactly what their name would suggest. They stop contaminated heating water from getting back into the drinking water lines.

Thermal expansion tanks are needed to absorb the expansion when the boiler heats the water. Because the normal hot water heating system runs under pressure and we want that pressure to stay at a constant, we must provide some room for that expansion. This is done with a thermal expansion rank. 

Tanks are pre-charged with air on one side of a sealed rubber diaphragm and the other side connects to the system and fills with water. Liquid is very hard to compress but the precharge of air within the tank can easily compress and allow the water to come into the tank. This allows the pressure within the system to be controlled.

Pressure relief valves are installed in the top of all hydronic boilers. This is a safety valve that will blow off pressure, if the boiler rises above thirty pounds. This can happen if the auto feeder sticks open, or if the boiler over heats. 



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As the Heat Flows

The baseboard end

So now you know how the system works at the boiler. Next the heated water flows along into the wall units. This baseboard assembly contains a pipe inside with fins that allow air flow.

This process is known as convection and here's how it works; As the heated water passes through the piping, the fins get hot and the air between them begins to naturally rise up and out of the enclosure. As this is happening air is leaving the enclosure and it starts to pull cold air up from the floor to fill the empty space. That air is in turn heated until it rises up and pulls in more and so forth and so on. 

The whole process is seemless and quiet and continues until the thermostat in the room or zone is satisfied. That's about it. A basic forced hot water baseboard heating system explained.

Thermal Expansion a Fact of Life

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