Steam heat is a rather simple way of heating a home. A gas or oil-fired boiler heats water, steam rises through pipes to metal radiators in each room, thereby heating the temperature of the metal which in turn heats the air. The steam then cools, condenses back into water, and runs down the same pipes back to the boiler. It is a very elegant solution that requires no pumps or fans, is very simple to maintain and will last for a very long time.
Over time, however, steam heating systems have essentially died out in favour of more efficient and easier-to-install forced air systems, so you will not run into a steam heating system unless you live in an older home or dormitory. Finding good advice on how to operate a steam system can be difficult, and finding any information on troubleshooting one can be nearly impossible.
Know your Radiator
One source of trouble is that people assume that all radiator systems are the same and will tell you how to work yours, never realising that there are at least three types. Single-pipe and dual-pipe steam systems operate somewhat differently and hot water radiators are completely different. If you follow the instructions for the wrong type of radiator you can end up with cold, sleepless nights.
A single-pipe steam system, as its name suggests, has a single pipe connected to the radiator. If you look at the base of your radiator and see pipes on both ends, you do not have a single-pipe steam set-up and this information won't be of much help to you.
Attached to the pipe leading to the radiator is a valve. This is a shut-off valve. It shuts off the radiator; that is all it does. This is definitely a nugget of information worth remembering.
The first mistake people make is to assume that they can control how hot the radiator is by turning the knob on the shut-off valve. Unfortunately, this is the worst thing you could do. Since the condensed water runs back down the same pipe that the hot steam comes up, you will force the steam and the water together, making bubbles. When bubbles burst inside a metal pipe or radiator, they make horribly loud banging noises. Keep the shut-off valve fully open or fully closed, and concentrate on the vent.
On the opposite end of the radiator, there is a steam release vent. These come in a few different varieties, but they all serve one purpose - they let the air out of the radiator, making way for the steam to come in. Most often, there is nothing to press or turn or twist on these, nevertheless the vent is what you use to control the heat output of the radiator. The basic premise is that if you control the amount of air that comes out of the vent, you control how much steam goes in, thus limiting how hot the radiator gets. You can replace the vents with other vents that allow airflow at different rates, or use ones with a variable setting. There are even temperature-controlled vents that adjust automatically as the temperature rises. The vents should not hiss, at least not loudly. If they do, this is a sign that there is too much pressure in your steam system.
The second mistake people make with radiators is to paint the vent. It is generally fine to paint your radiator, and this can even make it work better, but the vent has a hole in it (where the air gets out), and painting over the hole causes the vent to stop venting and the radiator to stop working.
Finally, if anyone tells you that you need to bleed your radiators, don't listen. Bleeding is a process that removes all gasses from hot-water radiators (necessary because air pockets would block the flow of water). Steam is a gas, so removing it from your steam radiators is just a stupid thing to do.
Your boiler will operate like most boilers or furnaces, with two exceptions: a glass water-level gauge, and water spigots. The gauge is easy - it lets you see how much water is in the boiler. The water level should be about 2/3 of the way up the water gauge. Then there are two spigots, one for letting water out, and one for letting water in. You can use these to adjust the level of the water in the boiler.
You should let some water out of the boiler on a weekly basis. The water inside the boiler tends to get very dirty, and letting some run out will go a long way to keeping the inside of your boiler and radiators from getting all gunked up. Carefully let the steaming hot water run into a bucket until it comes out clear, then check the level and add more water if necessary.
Once a year, have a technician look at the boiler to make sure all of the valves and safety devices are working properly. The technician will also clean the glass gauge if it has become too dirty to see the water level.
Boilers also have a pressure regulator that should be set to around 1 pound, and never changed. A common mistake when there is not enough heat is to increase the steam pressure, but this is just likely to break the vents on your radiators without solving the problem.
With minimal maintenance, your steam system should function correctly longer than you live. However, sometimes things go wrong, like one room getting too hot or another room staying too cool.
Primarily, this happens because steam systems are balanced to the needs of the house. The radiator is sized to match the size of the room, and the vent is carefully selected to allow just the right amount of steam into the radiator. But as time passes, vents get clogged or replaced with one of the wrong size, houses get insulated or rooms added, and the balance gets upset. If you need to readjust the balance, it helps to start in the room that has the thermostat and work your way outwards from there.
If a room is getting too hot, the first thing to do is check the vent on the radiator and replace it with one that has a smaller hole1. This will cause more air to be trapped in the radiator, preventing steam from getting in. You should also check the radiators in other rooms - if the vents are blocked or the radiators are shut off, it could force more of the steam to the one radiator which then produces too much heat. You can also purchase a radiator cover that restricts heat transfer (some will actually enhance heat transfer, so choose the right one). Finally, you can cover the radiator with a heavy cloth.
If a room is too cool check the vent to make sure it is not clogged or broken and replace it with one that has a bigger hole if necessary. Also make sure the shut-off valve is fully open. If you hear a knocking noise, that means water and steam are running together (and restricting the flow of steam) - in that case, make sure the valve is working and that the radiator is level or tilted slightly towards the pipe (so the water can run back down). Check the pipes running from the boiler to the radiator - these should be insulated. If they are not, all of the heat will be released in the pipes before it gets to the radiator, again upsetting the balance. Finally, you may need to call a plumber in case the pipes have become clogged. Don't worry if a radiator does not get hot but the room is comfortable - it just means that the radiator has been balanced to put out just a very little bit of heat without overheating the room.