Hot Water Heating Systems, was written for the average homeowner, who has a desire to understand the principles behind their residential hot water heating system.
The most popular type of heating today, hydronics, gives us a very comfortable living space through the convection process.
This is the physical law that states, heat rises. A natural phenomenon, in our world. Using this property to warm the areas we live in, is the most economical and comfortable form of heating, that is currently available.
Hot water heating systems start with a hydronic boiler.
Through out the history of the boiler, coal and wood have been used for energy. Fuel oil was introduced with steam and eventually natural and propane gas joined the mix.
Boilers of today will burn natural gas, propane, or LP gas. Heating oil is another source of combustion for this apparatus. Some will still appreciate the inexpensive use, of a wood burning boiler, however these have lost most of their appeal, due to the green movement and the higher efficiencies being achieve with gas and oil.
New High efficiency units,
Sequence of operation, is the understanding of what happens first, when a call for heat comes to the system.
A call for heat, will be initiated, when a thermostat is raised, or if the temperature of the room drops below, any thermostat setting in the house. This will close a circuit and tell the boiler somewhere in the house needs heat.
The thermostats are remotely located, throughout the house. Some homes will have one thermostat. This is known as a single zone system. The boiler is a very basic piping arrangement and the wiring and electrical controls are quite simple.
When we add thermostats, or more zones. They are placed in each area, we would like to control individually. When a call for heat comes to the boiler on a multi zone system, The boiler and control panel, will know which zone is calling.
Each of the zones of a heating system, have their own components. These items will be typical, for the most part, on all zones.
After an initial call, comes to the control system, a relay alerts the boiler, that a call for heat has arrived. The system responds by closing a circuit, which calls the burner for heat. at this time the burner may or may not fire.
Depending on the current temperature of the water inside the boiler, the system will fire, if the low limit, or lowest allowable setting, on our main control/ aqua stat has been reached.
This happens as water is circulated through the home to radiation and heat is expelled through the convection process previously explained.
Along the same line, there is a high limit on all boilers. This high limit acts as a cutout, for the burner only. This is usually between 170 and 210 degrees depending on the design of the system.
The high limit,
Backing up to the initial call for heat, the controls will also call the respective circulator pump for the corresponding zone. This pump will activate and begin to circulate heated system water to the radiation, for the room or area the zone services.
When the heat escapes, through the convection process around our baseboards, or the floor heating piping for radiant systems, the temperature will start to fall on it's way back to the boiler.
When the temperature coming back gets to the corresponding setting of the low limit, the boiler will re-fire and bring the water back to high limit before shutting down and starting the whole process all over again.
The pump from a calling zone, will continue to run circulating heated water, until the thermostat is satisfied, reaches the set point, or is turned down resulting in the same action.
When this happens the pump shuts down and a call is no longer present for heat. The entire system goes into stand by and waits for the next call to come.
Each zone has an individual switching relay, that sends a signal out, when it receives a call from it's respective thermostat. This signal calls the boiler and the corresponding pump, for that zone. The relay is activated, by the thermostat calling.
A simple two wire thermostat line, is all that's required to run a single zone, heating only, hydronic system. Heating thermostats have a very simple job. They open, or break the connection, when the temperature is satisfied. They close the circuit or connect our two wires, when a call for heat is desired.
A simple test to find out if your thermostat is working on a no heat call, is to remove the two wires and connect them together. If the system fires, then it's very likely the thermostat, that requires attention.
There are several other important components that are installed within each zone. Common to each loop will be valves, on our feeds and returns. These are not mandatory, to have a well functioning system, they are for convenience of service, for the many items, within each loop.
Also, this gives us the capability, to work on one zone, while the rest of them are still running. A third benefit, is not having to drain the entire system when working on an individual component.
The more valves, the better, ideally, but unfortunately not cost effective, a ball valve before and after, each component, will make servicing much easier.
Each zone, of a multi zone system will, require a flow check valve. This item is installed following the direction of flow, to stop a thermal rise of heated water, from occurring naturally when the water is heated.
This basic piece of equipment consists of a weight that is heavy enough to stop this gravity circulation, but is designed in a way to allow easy opening when suction from the circulator pump pulls from the other side.
This function keeps heated water in the boiler, from gravity circulating through the zones that are satisfied, when another one is calling. This unwanted extra heat, would override the thermostat setting and effect the functionality of the rooms heating control.
Flo check parts come in sweat, or soldered in models,
or cast iron threaded models,
Some systems will incorporate zone valves and some systems will have a separate circulator and relay for each zone.
Benefits of zone valves are, the initial cost reduction, to purchase and install, as well as versatility on systems, with many zones.
Zone valves are notorious for breaking down. They have in the past been manufactured with spring loaded mechanical operating devices that were very prone to failure. Todays zone valves have improved dramatically.
As with any product, time has provided innovation and now most zone valves, incorporate an electrical motor to operated the valve. This type of unit has turned out to be much more reliable, and is in wide use today. Costing a bit more, but adding extended lifespan, offsets the initial cost of the better zone valve. Plus we may save the potential midnight service call, that can cost hundreds, if not thousands of dollars.
The last component of a hot water heating zone, may be the most important element of all. A good purge setup. This is a combination of a boiler drain and a ball valve.
The boiler drain will have a male garden hose connection. The ball valve is shut off and then the boiler drain is opened, allowing city water to run through the automatic feeder into the zone and around the loop. then the water exits the system out the boiler drain.
This purging process is necessary when the system is initially filled. The air must be completely removed from the entire hydronic system. This is the only way to keep the circulator pumps from air locking when they encounter an air pocket. Air locked circulate pumps will eventually burn up as well as fail to provide heat to the corresponding area.
Purging is best accomplished, starting with the farthest zone from the boiler and working our way back to the closest. Power should be shut off to the system, to keep the pumps from fighting our efforts, and the flow check valves, should be wound open, to offer the least resistance.
Knowing a system needs purging, is relatively easier, then diagnosing some other problems. The system will sound like a river, running through your house. Air will babble along inside the pipes along with some water and sound like your favorite stream.
This problem can have several causes. Air could have been pulled in, through a leak in a circulator gasket, or some other small leak, on the suction side of any pump. This causes a small amount of air, to be pulled into the system, when this zone is called. The air introduced will mix in with the water and create this problem.
Another way air can get into a hot water heating system, is when a diaphragm type expansion tank, blows it's diaphragm. This causes the precharge of air inside these tanks, which is normally sealed off from the water to be expelled into the system.
This condition can be determined by tapping with a metal wrench, on first the top half of the tank, and then the bottom. The difference in pitch, will be substantial, if the tank is good. No difference in sound, will tell you the tank is blown and must be replaced. This condition will also usually make our pressure relief drip as well because we no longer have room for thermal expansion within the system.
One last way, that air can be discovered in the system, is when the installer has failed to properly purge the system at start up. Small micro bubbles that escape the purge process, will convene over time, making larger pockets within the piping. As this happens more and more, our noise will increase. Eventually left in the system, air can cause pumps to loose prime, and fail.
As you can see, maintaining our system as completely as possible, will be necessary, if service calls are to be avoided. Small problems will lead to larger ones, very rapidly. This can expand the heating budget immensely, as service calls are highly expensive.
The rest of the zone of heating, supplying our homes, consists of the piping, that runs to the location being heated. This will be made of copper tubing, steel pipe, or poly vinyl heat lines.
There is a feed pipe, leaving the boiler, carrying the heated water with it, for each of the zones. Once arriving in the radiation, the heated water expels it's heat through aluminum fins on baseboard heating, or into the flooring, with radiant heated floors and then exits the room and heads back to the boiler, to be reheated and repeat it's journey. This will continue, until the room thermostat is happy.
Each zone also has a return line, coming back to the boiler with the water to be reheated. This line along with all the returns, will be tied together with a manifold. This manifold will be sized to except the flow of water, the system will demand.
Incorporated in this manifold, are tee's to except each zone. There will be a return manifold and a feed manifold. The feed manifold will be the highest, of the two large lines to leave the boiler. Heat rises and again we want our hottest water heading out.
As the main feed leaves the boiler, there are several other items, we need to incorporate into our system. This is the equipment you will find, most systems will have, one instance of, irregardless of how many zones have been installed. They are common to all hydronic, or hot water, heating systems.
These types of systems, are closed loop Systems. Using city water pressure, or the pump from a well. The system is initially filled with water and then pressurized, to between 12 and 20 psi, or pounds per square inch.
This is accomplished with an item called an automatic feeder or auto feed valve.
Depending on the size of the system, larger volume homes, with a lot of zones, will need a higher pressure, as well as houses three, or more floors.
At any rate, the lowest pressure, within the 12 to 20 lb range, that will heat the home, is recommended. This lessons pressure, on valve seals and pump gaskets, extending their life span.
When the water is heated by the boiler, it is being done within the confines of a sealed system under pressure. This will cause a certain amount of thermal expansion. A method of controlling the system pressure at a stable 12 to 20 lbs, is a thermal expansion tank.
Without this tank, our system pressure would rise rapidly and control of the pressure, within the boiler and piping, would be unobtainable.
Too much of a pressure rise, will set off the pressure relief valve. This is a safety, installed, as well as required by all laws and codes, in every system, to keep the boiler pressure, from going over 30 lbs.
This valve is usually installed directly on the top of the boiler with NPT, or National Pipe Threads. There will be a discharge pipe leaving the valve that will terminate 2 to 6 inches from the floor depending on the state you live in as this code varies from state to state.
The purpose of this pressure relief valve is two fold. The relief valve itself and the down pipe to protect anyone standing near the equipment from getting scalded should it unknowingly go off.
The discharge pipe, may be run away from the boiler, to protect flooring. Discharging at a remote location, out of harm's way, is the idea we're after here.
Sometimes the pressure relief will drip and and there are several causes for this to occur. These valves are preset to go off when the pressure exceeds 30 lbs.
This can happen if the automatic feeder on the system, which controls the input of makeup water, malfunctions and allows unbridled, city water pressure to enter the system.
Normally city water pressure can run anywhere between 25 to 100 lbs of pressure. This will overfill the system and cause the pressure relief to do it's job and relieve the pressure. A slow leaking auto fill valve, will cause this issue.
Another cause for a non faulty pressure relief valve to leak, is a bad thermal expansion tank. This is a very common problem in home heating systems.
There are two types of expansion tanks, in use today. Both types have one pipe usually tied into the feed manifold. above the boiler, this tank holds enough air, that can be compressed. This compression of air, makes room for the heated water to expand in.
A diaphragm expansion tank, consists of a small bottle, about the size of a barbecue grill propane tank. this equipment as it's name suggests, has a rubber diaphragm across the center dividing it in half. The top of the tank which is open to the system will have water in it. The bottom half is precharged with enough air to absorb our thermal expansion.
Type two expansion tanks are actually the older type. This method uses a steel tank with no air charge. There is a feed from one end usually half inch pipe, tying in as with our previous tank, to the feed manifold, somewhere near the boiler. This tank is shut off from the system and water is drained from a boiler drain in one end, then the drain is closed and the tank is filled with air at atmospheric pressure. When the valve to the system is reopened, the pressure in the system compresses the air in the tank and leaves room for thermal expansion.
Air can be very easily compressed and water can't. This is why these methods work to maintain a stable pressure when we are trying to control, thermal expansion.
The previous mentioned automatic feeder is also an item that is commonplace to all systems of this type. This maintains a constant pressure in the system should a leak develop. These valves are also a common problem resulting in service calls. When this item malfunctions, either pressure drops, because the valve failed to replace lost water, or the valve sticks open and adds more water then we want.
Repair kits are available for auto feeder valves and are minimal in cost compared to a new valve. Repairing them can differ in labor, depending on how many, and where your valves are, that control this item.
New codes introduced in certain areas, will require a back flow preventer,
A grasp of the functionality of our homes heating, is a good thing to have. Knowing whats what will enable us to locate a valve to shut off in the case of a leak. This can save the damage that would occur waiting for the serviceman.
Understanding the serviceman's terminology, when they come to your home on a call, is a great thing, when deciding if where getting a good, fair price on parts as well.
There is also a comfort and peace of mind that comes with understanding how where going to keep warm, through the harsh winters, that can occur in some places.
Although this article is now the source to go on line to discover how your hot water heating system works, it has not qualified you to work on this system. This should be done, only by servicemen and women, who have been formally trained in heating.
All plumbers and heating technicians have undergone extensive training to become competent to work on this complicated mechanical system. They have been licensed and should carry the proper amount of liability insurance for the job.
Most local codes, prohibit plumbing and heating work from being done without first obtaining a plumbing permit and these rules are important to follow, as ignoring them can cause harmful conditions.
When a service company does need to be called to work on our home heating, having a grasp on what's being discussed, will give you an added edge, to help guard against any unscrupulous serviceman coming in with a ridiculous price. It's much harder to pull the wool over the eyes of an educated consumer. Hopefully now that you've found this article on Hot Water Heating Systems, that's exactly what you are.
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