One of the nicest things about older houses -- we think -- is the "interesting" old heating systems -- the tank in the bathroom, the pipe that runs through the roof, the pipes that rattle and clank like Marley's ghost, the radiators that hiss and bang.
Sure, it may occasionally be noisy, and it may need more care and feeding than your average modern forced-air system. But it's great heat, steady, efficient and draftless, and once you understand how it works, it will be fairly clear when repairs are in order.
Basically there are four types of boiler heating systems: circulated hot water; closed-gravity hot water; open gravity hot water; and steam. Any of them may be fueled by gas or oil -- or, in some rare instances, wood or coal.
All of them operate by heating water so the water, or its steam, rises through metal pipes to "radiators" throughout the house.
The circulated hot water system is the most mechanically complicated of the three hot-water types. As explained by David Culver, of Bryan Plumbing and Heating of Parkville, this system uses an electrically operated "impeller" to pull water through the radiators. It includes a pressure-reducing valve, which cuts the pressure of water arriving from the street connection from 45-60 pounds per square inch and maintains it, by automatically adding more water as needed, at a standard 12 psi; and a pressure relief valve, which "blows" if the pressure in the boiler exceeds about 30 psi.
Maintenance includes keeping the pressure properly adjusted so all the radiators fill, keeping the area around the heating element dirt-free and keeping the circulator oiled.
The two types of gravity systems are the simpler mechanically, though, without the circulators, they may require more attention to keep the pressure properly adjusted and all the radiators working.
The open-gravity system is identified by a tank located in a high part of the house -- often a bathroom or closet on the top floor. The tank has a "sight-glass" that allows you to check the water level in the system and a pipe that runs out to the roof or through the wall to the outside.
The sight-glass system has a couple of problems: it may get clogged or so cloudy it can't be read; and even if you can read it, you still have to run to the boiler in the basement to add water. In addition, the open-gravity system doesn't have a pressure reducer valve. To add water to the system and raise the pressure, you open the valve to the 'street' source and close it again when enough water has been added. If too much water is added and the pressure gets too high, the excess runs out through the pipe on the roof or through the wall.
Closed-gravity systems rely on the natural rise and fall of the heated water. They don't have circulators, and they may not have pressure-reducer valves. Most have pressure relief valves. If the water pressure gets too low, more water is added to the system by opening and closing the valve from the main line from the street.
In a steam system, the water stays in the boiler and steam circulates through the pipes. As it cools, it condenses and runs back into the boiler through "condensate-return pipes." There's no circulator, and each radiator has its own air vent, which acts as a pressure-release valve. Steam boilers also have a sight gauge to indicate how much water is in the coils. Water can be added by opening a valve; many steam boilers have pressure-reducer valves that add water automatically. Many steam boilers have cutoff devices that shut the system down if the water level falls too low.
Older systems may have problems with condensate return pipes clogging, so water can't get back to the boiler. This may be a special problem with galvanized return pipes. When the water can't get back, the level drops in the boiler and the low-water-cutoff device shuts down the system. If there's no automatic-fill valve, the system simply stays down until the water finds its way through the clogged lines and raises the level again.
An automatic-fill valve may complicate such a problem; when the water can't get back and the level falls in the boiler, the automatic filler adds more water to the system -- and can overload it. If there's water coming out of the radiator air vents, the system has too much water, not too little.
If you're replacing a boiler in a rehab, it's a good idea to spend a couple hundred dollars extra to replace old condensate return pipes with new copper pipes.
If one or two radiators in a steam system aren't heating, it usually means that air is clogging the pipes. The radiator air vents may be painted shut, clogged or even full of water. The steam mains may also have too much air; they should have vents beyond the last rising pipe that allow air to escape.
Radiator air vents aren't expensive; you should probably replace all of them when you rehab a house with a steam system.
It's probably a good idea, at least the first time you encounter a problem, to get a plumber to lead you through the process. Each of the systems has its quirks. Diagnosing and resolving the problems of a steam or water heat system aren't always simple, and if something goes wrong, you could really be in hot water.
Next: A look at some new home-improvement books.
Mr. Johnson is construction manager for Neighborhood Housing Services of Baltimore. Ms. Menzie is Home Editor of The Sun.
If you have questions, comments, tips or experiences to share about working on houses, write to us c/o HOME WORK, The Sun, 501 N. Calvert St., Baltimore, Md. 21278. Questions of general interest will be answered in the column; comments, tips and experiences will be reported in occasional columns.