Residential and Light Commercial Low Pressure Steam Boilers
The residential steam boiler is still alive and well despite the fact that some HVAC professionals refer to it and the steam boiler profession as the dead mans club. However, there are not a lot of HVAC boiler technicians or HVAC companies that specialize in steam boilers because there are not a lot of the steam boilers used for residential and light commercial applications. People have either converted their old boiler steam systems over to hot water or have gone with forced air systems. The concept is simple but the mechanics of it can be frustratingly complex when a problem occurs unless you have the experience and knowledge that comes with working on the residential or light commercial steam boilers. Before we dive into some of the problems that arise with steam boilers, we’ll cover safety first. After all, HVAC safety is the most important aspect to any home heating system.
Steam Boiler Safety
The steam boiler must super-heat the water inside the water cavity to more than 212 degrees F. If the proper controls are not in the system a steam boiler can reach dangerous temperatures and possibly cause a fire. For a steam boiler to operate at the proper temperatures it needs some basic safety controls. Some of these are:
- Limit switches which will open if the temperature rises above a certain set point need to be in the system. Limit switches (manual reset) located near draft diverters will shut the system down if the chimney or flue gets plugged up. This prevents carbon monoxide poisoning or conditions. Limit switches near the burner manifold detect roll-out and prevent fires or worse.
- Low water cut-off. If the water in the water jacket falls below a certain point a dangerous condition will exist. The water level in a steam boiler should never go below half-way in the sight glass. Dirty sight glasses should be cleaned. Additionally they should be checked to ensure that they are not plugged with crud of some sort. A regular visual inspection of the sight glass is good practice especially in the heating season.
- Automatic water feeder. An automatic water feeder, when functioning properly, will keep the steam boiler water level at the necessary levels needed to maintain good steam heat. Minor adjustments are necessary so that the right level is maintained in the boiler. Too much water and the system will not heat. Not enough water and a dangerous condition can exist.
- Residential steam boilers operate under very low pressure conditions. However, a large volume of low pressure steam can be a danger. For this reason there are pressure controls on the boiler. Normally set at 2 P.S.I., the pressure control will shutdown the system if too much pressure is sensed by the pressure control. There are redundant features to the pressure cut-off control. A pressure relief valve should be maintained on the boiler. If the steam boiler exceeded the pressure of the rating on the relief valve, the relief valve would open and release pressure. The steam boiler should be blown down once a week during the heating season or while it is in use. Blow down valves are found on the water feeders and low water cut-offs. It looks like a lever and most are yellow (some are red). These valves should be opened allowing the water to flow into a bucket or sump. Water is normally drained until it is clear or you fill a five gallon bucket. This ensures fresh water is introduced into the steam boiler on a regular basis and can help keep the cruddy deoxygenated water out.
Steam Boiler Common Problems
- Water Hammer or banging pipes. This is a common problem that can be reduced if not eliminated with the proper devices. Water hammer occurs when the condensed water meets the steam. Cool water meeting hot steam causes the pipes to expand and contract rapidly. This makes it sound like someone is down in the basement beating on your pipes with a hammer. The system could have a problem with the return condensate water getting back to the Hartford loop and eventually the boiler. It could mean a strainer or trap is plugged with sediment and limiting the return of condensate water returning to the boiler. The automatic water feeder will continue to keep the water level in the steam boiler but the system will have too much water in it and the mains will flood. It is important to keep the return piping system efficiently returning water to the steam boiler to prevent water hammer. Consult an HVAC professional about reducing or eliminating this problem.
- Steam Vents leaking water. Steam radiators on one pipe systems should not be level. Often the floor will settle and the radiator will begin to leak water from the steam vent. A shim can be placed under the legs of the radiator opposite the pipe. This will allow the condensed water to drain out of the radiator back to the return line to the boiler. If after placing a shim under the radiator and the leaking continues, consult an HVAC professional.
- Radiators not heating. This can be the result of several things depending on if the radiators are two-pipe or one-pipe. First check to make sure the valve is open at the base of the radiator unless it has a thermostatically controlled valve. If it is one-pipe the thermostatically controlled valve will be at the steam vent. If it is two-pipe this valve will be on the supply pipe coming into the radiator. If you turn the thermostat all the way down the valve should shut. Turn it all the way up and the valve should open. If none of these things work it is probably best to consult an HVAC professional.
- Total Dissolved Solids (TDS) can build up in the boiler if a blow-down of the steam boiler is not done on a regular schedule or set frequency. Dissolved solids in the water that are caught in the steam settle in the steam boilers. Without regular blow-downs the solids build up and cause problems. Additionally, they reduce efficiency and create safety issues. This is something usually done by the homeowner or maintenance person (if it is a business) but should be done according to the advice of an HVAC professional as far as blow down frequency is concerned.
- The build-up of carbonic acids can eat through hydronic piping and needs to be addressed by either venting oxygen and CO2 or having water treatment. Consult and HVAC Boiler expert for more information.
Learn more about hot surface igniters on the Furnace Page. The following is an excerpt from the furnace page and is related to boilers.
Characteristics and Behaviors of the Gas Furnace Flame
The flame that your furnace or steam boiler produces can effect the performance and efficiency if it is not properly burning the fuel. A professional HVAC Technician will have high tech tools so that your furnace can be tuned to where the mixture, fuel and air, is proper ensuring the furnace is getting the maximum amount of efficiency possible. This is super important considering that the cost of fuels, whether it is natural gas, propane, or oil, is continually rising. The first test that can be performed on your furnace is simple and requires no tools, but does require a knowledge of what a proper furnace flame should look like. Natural Gas should have blue flame with a very minimum amount of yellow tips on the top of the flame. Too much yellow tips would mean there is not enough primary air or a combination of some other problems where a simple adjustment can be made to correct the problem to get the most out of the combustion process. Problems other than yellow tipping are rollout, flashback, lifting flames, and floating flames. All these problems should be corrected to get the most out of your furnace or boiler . The next test that can be performed is the combustion analyzer test. An expensive tool must be used for this test. An electronic device that is capable of reading and analyzing several processes of combustion can give the technician clues about any potential problems so that some sort of action can be taken to correct it.
A furnace combustion analyzer will tell the furnace HVAC technician the stack temperature, carbon monoxide level, carbon dioxide level, and oxygen levels in the exhaust gases leaving the furnace. This furnace test should also be done in conjunction with a furnace draft pressure test. It is important that all the by products of the furnace combustion process are exhausted outside the home. A furnace draft test can determine this will happen. A visual furnace test using a mirror can also be done to ensure there are no blockages of the chimney or the furnace flue. All the byproducts of the furnace combustion process are analyzed and measures taken to correct any abnormal readings by making adjustments according to furnace manufacturers recommendations. Finally, the last furnace test that can performed is a gas pressure test. These pressures are different from one furnace or boiler to another and from natural gas to propane to oil. Propane and Natural Gas are measured in water column inches using a manometer. It is important that the proper furnace fuel pressures are present in the furnace or boiler not only for furnace/boiler efficiency purposes but also for complete furnace fuel combustion. All these furnace test can performed by a qualified furnace HVAC technician and can make a big difference in the amount you pay for the heating fuel you use over the colder months. Call to schedule your furnace or steam boiler tune-up today.