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Steam Heat

Steam Heat Basics

Here are some facts and things to consider if you own a house with Steam Heat.

Steam heat is a warm wonderful way to heat a house. I consider it a special plus on our old house, and wouldn't trade it away for any other system. It does have its draw backs and its own special nuances though.


Because the temperature of the fluid heating your house (steam) is 212 F or a little higher, the temperature of the flue gases can not be lowered below that temperature. What this means is, you will always need a masonry chimney, and you will never have efficiencies that the new gas and even the new oil fired hydronic (baseboard water) or air systems have. Low 80s is as good as you can expect. When you have it tuned each year, you should look at the efficiency number. It should be above 80%, but don't expect much more than that.

Air Venting

Each time the boiler kicks on delivers steam to the house, it must push the air out of the pipes and radiators. Those vents are key. If a radiator is not getting hot, replace that air vent on the end of the radiator.

The radiator vent may have numbers on it. Typically the higher number setting will vent the air faster, and the radiator will heat up quicker. Sometimes it will say "fast" or "slow", sometimes it will only have the numbers. Ideally, for a small radiator, you can use a smaller number, and for the larger radiators you would use the large numbers. The idea would be to get all the radiators to reach full heat at the same time. But if you have a cold room, you may want to use the faster setting regardless of the size of the radiator.

In the basement, on your main lines, there should be at least one large air vent per loop to remove the air from those lines. This makes the steam get to the radiators quicker. If these are not working, all the air in the lines must be purged out at the radiators themselves. This will slow the rate of heating up in the radiators significantly. Some may never get a chance to get hot. Check and replace those air vents on the main lines!

Operating Pressure

The setting on your boiler for cut in and cut out is controlled by the pressuretrol. The pressure it cuts in at should be set at 1/2 pound (.5 psi) and the pressure it cuts out at should be 1 pound higher at 1 1/2 pounds (1.5 psi). This should be enough pressure to move the steam in your house. If you don't know how to adjust this, have it adjusted by your service tech next time your boiler is tuned up.

If you find that the pressure is adjusted DOWN significantly from where it was to get the .5 to 1.5 operating range, monitor your system's operation. If some radiators are not getting hot, check and replace the main line air vents. The system's pressure may have been raised (erroneously) to compensate for nonworking air vents.

Low pressure is safe. Overpressure is NOT safe.

Low water cutoff

Be sure your boiler has a functioning low water cutoff. Steam systems lose a little bit of water all the time, so there has to be water makeup. Some units have an auto feed, some are done manually. In either case, you want to be sure, the unit will shut off if there is low water. Firing an empty boiler will destroy the boiler and perhaps worse... Check the cutoff regularly and check your boiler's water level weekly

If you have a low water cutoff with a float, flush it at least once a week. This will keep the rust and gook from collecting in it and preventing it from working.

Pipe Insulation

All the piping in the basement leading to from the boiler to the radiators should be insulated. It may have had the old insulation removed in an attempt to get rid of asbestos. But these pipes should be insulated. It will eliminate or reduce the amount of water hammer (that Bang Bang bang) you may be having when the system is fired up. Be sure to use pipe insulation rated for steam piping.

Radiator pitch

Check the radiator with a level. It should be slanted toward the supply pipe. If it is not, raise the vent end with shims to get it level. Small pieces of wood or tile will work. I know in my house, every radiator had sagged with time and needed to be pitched correctly. It doesn't need to be pitched much toward the supply, just a little bit will do.

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Finding Help

If you have trouble with your steam heating system, ask around. You need to find someone that is familiar with steam heat. It is different from a hot water system, so you may have to look for a while before you find someone. Steer clear of people that don't think there is much difference, and don't let anyone raise your system pressure to get the system to work better. The answer is usually fixing the air vents.

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