Steam Heating: Don't Let Me Be Misunderstood

Bill, we’re buying a 100+ year old home with steam heat and found your article on old boilers.  Our home inspector made a comment about it being an outdated, inefficient way of heating.  He recommended changing to a water circulator system that operates at a higher pressure.  I was surprised to find it still using steam since the boiler was replaced 4 years ago.  What do you think about steam systems.

I still get excited every time I see a steam heating system.  I think your inspector probably gets scared.  The basics of residential steam heating systems are simple.  After the guys that designed and installed these old systems died, it became complicated.

There are two reasons I enjoy seeing old steam heating systems.  First, I see them as a perfect fusion of technology and art.  The incredible details of the individual parts from the manufacturers, combined with the ingenuity of the installer, results in a dynamic creation that extends throughout the entire building.  Second,  I’m amazed at how many of these enduring systems have kept a couple generations of families mostly comfortable and healthy for well over 100 winters.     

It’s Not About Pressure

In steam heating boilers, water is heated until it becomes steam.  Liquid has now changed to a gas.  Steam then travels through the piping to the radiators in a home because of only a very slight pressure difference.  The pressure in the system, created by the increase of volume when liquid changed to gas, only needs to be enough to overcome the friction inside the pipes.  The piping was typically designed and installed to keep this friction very low.  Since the earliest times of residential steam heating, systems were designed to operate at less than 2 pounds per square inch.  If pressure is increased in the system, you end up compressing the steam (a gas, not a liquid).  This results in the steam moving slower and needing more water heated at the boiler to create the steam.   Low pressure is better than high pressure.  In fact, there’s some systems that work in negative pressure, called vapor/vacuum systems.

As the steam travels through the pipes and to the radiators, it gives up heat.  The steam then condenses back to water.  The condensate water then needs to find its way back to the boiler.  In some systems, the condensate drains back in the same pipe as the steam is being delivered.  Other systems have a second pipe to return the water back to the boiler.

It Worked Better Before

When these old steam systems were installed, they had a better understanding of how to size the boiler, size and configure the piping and what accessories were needed to keep a steam system working properly.  The biggest problem is when changes occur to the original system that alters the original dynamics.  Originally these were coal-fired systems that had a nice hot, perpetually burning fire.  Most systems now have been converted to gas or oil fired systems that cycle on and off frequently.  Many old boilers have been entirely replaced with a smaller, lower water content boilers.  When the update occurs, the critical to steam, near boiler piping configuration gets changed.  Over the decades, parts wear out, break, rust or become clogged and need replacement – often with parts that don’t function exactly like the original.  Even having the asbestos-containing insulation removed from the pipes can create issues.

After any of these changes occur, many systems don’t operate exactly as before. Water can be drawn up into the supply pipes with the steam, the steam condenses before reaching all radiators, condensate doesn’t make it back to the boiler or a loud “water hammer” in the pipes are some of the issues that can occur.  Some issues aren’t obvious and are only identified after the cost of heating the home increases tremendously after a change or “upgrade”.

The second most important part of owning a steam heating system is regular maintenance.  The most important is retaining a good heating contractor.  There are fewer and fewer that have the knowledge and skills to keep these systems working properly and efficiently.  In my experience, a majority of the those sent out to evaluate, service or repair these systems don’t fully understand them and try to sell an “upgrade”.  If you find a great steam heating service technician, offer him tips, meals, or whatever it takes to have him consider you a “preferred customer”.