The function of a steam boiler is the same as any other central heating system. The goal is to heat the house, making it comfortable in a safe and economical fashion.
Steam heating has some advantages. The principle is simple and there are few moving parts. There is no fan or pump associated with moving the heat through the distribution system. (There are exceptions, but for most small residential systems, this is true.)
Steam heat also has some disadvantages. The working environment of a steam boiler is harsh because of the high temperatures and the changes of state that take place. The interior components are variously exposed to air, water and steam.
Because steam heating systems are not being used in new construction, many service people are not well qualified to work on steam systems. There are very few people left at the residential service level who have designed steam heating systems from the ground up. Modern commercial steam systems are very different from older residential steam systems. This poses another challenge to service people who may not be used to working on house steam systems.
Because steam heating systems are not manufactured in large quantity anymore, parts can be difficult to obtain.
Steam heating systems can be difficult to evaluate because there are so many different systems. There are several unique proprietary systems, each with their own characteristics. Many of these will no longer be in their original state or original arrangement.
The problem is compounded because most older systems have been modified to some extent. Vents and traps may have been added, abandoned or removed. Gravity return systems may have been converted to pumped return systems. Dry returns may have become wet returns, by design or by accident. You get the idea.
Steam heating is slower to respond than forced air and hot water heating systems.
The radiators on steam heating can be very hot. We're dealing with steam on one side of a cast iron radiator that is usually slightly above 212F. The surface temperature of the cast iron radiator can be hot enough to burn skin. In this respect, steam heating is a little dangerous, especially for children.
Although well-designed and maintained steam heating systems should be as quiet as hot water systems, the reality is that many are not in good working order and these systems can be noisy. The noise can be
is a feature of the system. We'll look at water hammer shortly.
Because we are dealing with a change of state and higher temperatures than with hot water boilers, steam boilers can be more dangerous. However, both steam boilers and hot water boilers are safe as long as the proper safety controls are in place and in good operating order.
Connections for gauges and pressuretrols have pigtails that hold water to shield the device from direct contact with the steam. This is one way to identify steam boilers.
We have already suggested that there are lots of different kinds of steam heating systems. We will mention a few of the common categories just to give you an idea of what we are dealing with:
systems. Low pressure systems operate at 15 psi or less. Most residential systems will be low pressure.
There can be
systems. The one pipe systems are older and the two pipe systems are modern. You will see both in houses.
One pipe systems can be
. In a parallel flow system, the condensate runs in the same direction as the steam. In a counter flow or
system, as they are sometimes called, the condensate runs in the opposite direction to the steam.
Steam systems can be
systems. Most homes have an upfeed system.
Steam heating systems can be classified as
. The pumped return systems have a
boiler feed pump
. Gravity return systems rely on gravity to return the condensate to the boiler.
, which are very low pressure (only a few ounces of steam).
, which operate below atmospheric pressure.
which are a hybrid.
When we come across steam systems, which are rare in our working area, we call for help from a specialist. Because we don't see these systems regularly, it is difficult for our people to have a good working knowledge of them. Also, because there are so many different types, it can even be difficult for us to know which type we are looking at, especially since many of the older systems have been modified and are no longer pure systems.
We are particularly cautious because steam heating systems may appear to be working fine during the middle of the day. However, at night or during a start up phase, there can be considerable water hammer, noise and even leaks that will not be apparent at other times.
Steam heating systems can be expensive to work on because there are so few qualified people available.